altitudinal and seasonal distribution of orthoptera in the rocky mountains of northern colorado

Altitudinal and Seasonal Distribution of Orthoptera in the Rocky Mountains of NorthernColoradoAuthor(s): Gordon Alexander and John R. HilliardSource: Ecological Monographs, Vol. 39, No. 4 (Autumn, 1969), pp. 385-432Published by: Ecological Society of AmericaStable URL: http://www.jstor.org/stable/1942354 .

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ALTITUDINAL AND SEASONAL DISTRIBUTION OF ORTHOPTERA IN THE ROCKY MOUNTAINS OF NORTHERN COLORADO'

GORDON ALEXANDER AND JOHN R. HILLIARD, JR.2

Department of Biology, University of Colorado, Boulder 80302

TABLE OF CONTENTS

ABSTRACT ............. ................. 385

INTRODUCTION .............................. 386

ORTHOPTERA AND ALTITUDE ....... ................ 386

DESCRIPTION OF REGION .......................... 387 General Account .............................. 387 Collecting Stations ............................. 390

NATURE OF OBSERVATIONS ....... ................. 396

RECORDS OF INDIVIDUAL SPECIES ...... ............. 397 Introduction .............................. 397 Non-Saltatorial Orthopteroid Groups ..... ...... 398 Tetrigidae ................. ............. 398 Acrididae ................. ............. 399

Romaleinae .............................. 399 Cyrtacanthacridinae .......................... 399

Catantopinae ................................ 399 Oedipodinae ................................. 406 Gomphocerinae .............................. 411

TETTIGONIIDAE ................................. 415

GRYLLACRIDIDAE ................................. 416

GRYLLIDAE . ................................. 417

DISCUSSION ................................. 417 Altitudinal Zonation ............................. 417 Altitude in Relation to Latitude ................ 421 Altitude in Relation to Phenology ..... ......... 423 Altitude in Relation to Species Diversity

and Population Density .................... 426

ACKNOWLEDGMENTS .............................. 428

LITERATURE CITED ................................ 428

Abstract. Ninety-four species of Orthoptera (s. lat.) occur along an altitudinal transect from 5,000 ft (1,530 m) to above 14,000 ft (4,265 m) in the Front Range of the Rocky Moun- tains of Colorado, near 400 N. Lat. These were sampled, with observations on life histories in relation to altitude, at a series of altitudinally spaced stations during the seasons of 1949, 1958, 1959, and 1960, the stations being selected for maximum variety of Orthoptera at each altitude. Other observations of the past 35 years were added. Sampling was by a sweeping technique designed to be qualitatively exhaustive of species and age groups; it was thus quasi- quantitative. Times of hatching, times of different juvenile stages, and times of maturing were determined for species at the different altitudes at which they occurred. These data are summarized by species, the 94 species being in the following families: Mantidae, 2; Phasmidae, 1; Tetrigidae, 4; Acrididae, 73; Tettigoniidae, 8; Gryllacrididae, 3; Gryllidae, 3.

Numbers of resident species found in 1,000 ft altitudinal bands were as follows: 5-6,000 ft, 71; 6-7,000 ft, 49; 7-8,000 ft, 34; 8-9,000 ft, 25; 9-10,000 ft, 19; 10-11,000 ft, 15; 11-12,000 ft, 9; over 12,000 ft, 3. Larger average numbers of individuals per species occur at higher elevations. Many more species of low frequency occur at low altitudes than high, the total number of species known from a given high altitude station often being present in a single collection, while, at low altitude stations, even the most varied collection lacks species occasionally collected there. The reduction in species numbers with altitude is correlated with a similar reduction with latitude, and the geographic distribution of particular species of Orthoptera is correlated with altitude. Of the 18 species of Acrididae recorded north of 600 N. Lat. in North America nine are common to abundant in the area of study up to 10,000 ft, six of these to 11,000 ft or more. However, three strictly montane species from above 10,000 ft are not known from the far north. The altitudinal distribution of the 36 most common species provided a basis for testing various suggested schemes of altitudinal zonation.

A few high plains species that feed only on forbs are apparently restricted in part by the distribution of host plants, and a few grass-feeders do not invade the grassy clearings in montane forest, but the majority of species occurring on the high plains do range into clearings in the lower montane forest up to about 7,000 ft. Pest species with wide altitudinal ranges are essentially indiscriminate plant feeders. The reduction in number of species of Orthoptera with altitude is much greater than the reduction in number of plant species, so variety of plants is not a limiting factor in their altitudinal distribution. A more important factor is apparently the length of growing season-in particular its abbreviation at the end. Evidence for this is the occurrence of early juvenile instars of some species above the altitude at which the species normally completes its life cycle. Evidence was found for the relations between phenology and altitude postulated by A. D. Hopkins in the times of maturing of species with wide altitudinal

Manuscript first received November 14, 1968. Accepted for publication June 17, 1969. 2 Present address: Department of Biology, Sam Houston State College, Huntsville, Texas 77340.



386 GORDON ALEXANDER AND JOHN R. HILLIARD, JR. Ecological Monographs Vol. 39, No. 4

ranges, with events somewhat earlier than expected at the highest altitudes. Events that occur near the middle of the summer (hatching of eggs of species that overwinter as juveniles) are independent of altitude, but this too is in harmony with the Hopkins law.

INTRODUCTION

Orthoptera are ideal tools in the study of ecological principles. They are widely distributed, conspicuous, easily observed and collected, well known taxonomically, and readily studied under laboratory conditions. Individual species often have specialized requirements, and the numbers of species and individuals are large enough for striking ecological differences to be evident within a single community as well as among communities.

These advantages prompted the senior author to begin, in 1931, the use of Orthoptera as tools in the study of various ecological aspects of altitude. The continuing purpose of this study has been to determine to what extent the distribution and seasonal occurrence of members of this group are in- fluenced by altitude-with the hope, of course, that the findings may have a wider significance than merely for this group. With occasional interrup- tions, some seasons involving extensive field work and others including only a few observations, these studies of Orthoptera in relation to altitude have continued to the present.

By 1957, accumulated observations were extensive enough to justify a concentrated, more elaborate field program. Support by the Na- tional Science Foundation, with the junior author as research associate, provided for rapid and comprehensive expansion of the study. The summers of 1958, 1959, and 1960 were devoted full time to an analysis of the distribution of Orthoptera along an altitudinal gradient in the Rocky Mountains near Boulder, Colorado. Five or six persons took part in the project each of the three seasons, and data from over 60,000 specimens were obtained. Studies have continued to the present but on a more modest scale.

The present paper summarizes observations on altitudinal and seasonal distribution of the 94 species of Orthoptera (s. lat.) found in the region of intensive study. It deals primarily with altitudinal distribution and with phenology in relation to altitude but also considers other ecological aspects. It is the first comprehensive summary of the distribution of Orthoptera along an altitudinal gradient in the Rocky Mountains.

Previous publications dealing with altitudinal distribution of Colorado Orthoptera have been either on alpine species primarily or have recorded observations on altitudinal distribution incidental to general distributional studies. The former, like the latter, have been primarily faunal or taxonomic

(Scudder, 1898; Chopard, 1928; Hebard, 1936a), though one dealt with ecological principles (G. Alexander, 1951). None has considered phenology in relation to altitude. Among general distributional studies, Hebard's (1929) paper on Colo- rado is most important, though Hebard employed ambiguous topographic categories to suggest altitudinal ranges his "mountain valleys," "mountain foothills," and "mountains from foothills to timberline" being overlapping categories.

The most comprehensive studies of Orthoptera in relation to altitude have been in the palearctic region. Many have appeared since Uvarov's general account (1928), some primarily faunal (e.g., Ander, 1949; La Greca, 1966; Pravdin, 1964); others primarily ecological. Dreux's study in the French Alps (1962) is perhaps the most extensive of the latter group, but others have involved the Pyrenees (e.g., Marty, 1961), the mountains of eastern Europe (e.g., Bey-Bienko & Peshev, 1960; Peshev & Maran, 1963), and the mountains of central Asia (e.g., Pravdin, 1962). just as in North America, too, certain general faunal accounts have also included much material on altitudinal distribution (e.g., Harz, 1957; Ramme, 1951).

ORTHOPTERA AND ALTITUDE

The most extensive summary of insect distribution in relation to altitude is in the recent works of Mani (1962, 1968). One of his conclusions (1962) is that the high altitude environment is essentially "a single, indivisible and complex factor," that its elements may have to be studied separately for convenience but their interactions are so complex that "the sum total . . . is itself a factor." It is not our purpose to elaborate on this theme, though Mani's point is well taken. Alti- tude does involve a complex of environmental components; environmental concepts with which it is comparable are not such things as light and temperature but, rather, climate and latitude.

Altitude as a factor of the environment is para- mount in the region of our study, so it has been the focus of our attention. We summarize our observations on orthopteran distribution primarily in relation to altitude as such, not in relation to its several components. We do suggest the possible role of certain components in specific cases, providing support for such generalizations with data from our observations, but our studies necessarily lack the detailed habitat correlations that have



Autumn 1969 DISTRIBUTION OF ROCKY MOUNTAIN ORTHOPTERA 387

characterized previous ecological studies of Orthoptera in smaller, more circumscribed areas.

In mountainous regions, the significance of altitude in distribution is similar to that of latitude, as is known for numerous organisms, especially plants. The following generalizations can now be made on the basis of our observations of Colo- rado Orthoptera: 1) At a given latitude, a range of altitude is accompanied by gradients in numbers and kinds of species, gradients that resemble those associated with latitude except that they are con- densed into a shorter distance. 2) Mountains with a north-south trend, such as the Rockies, carry many species far south of latitudes where they occur at lower altitudes. 3) A species with a wide altitudinal range appears later in the season at higher altitudes, and it must there be adapted to a shorter growing season. 4) High elevations in the southern part of a range may have retained small, quite circumscribed, relict populations of northern species after the northward retreat of ice-age cold. 5) High elevations isolated by low altitudes from other high elevations nearby have faunas resemb- ling in variability those of an archipelago. Our observations support all these generalizations. While evidence for statements 4 and 5 is included only in our treatment of individual species, that for the first three statements is developed rather fully in our DISCUSSION section.

These effects of altitude are reflections of major climactic variables also associated with latitude, but all environmental components of these two complexes are not comparable. The decrease in atmospheric pressure with increasing altitude con- stitutes an obvious difference between altitude and latitude. The accompanying decrease in partial pressure of oxygen does limit the vertical distribution of higher vertebrates but is probably of little significance in the distribution of Orthoptera. The effects of altitude on insects are primarily in- direct; they more likely reflect climatic gradients that are themselves the results of the gradient in atmospheric pressure.

There are two other important differences between latitudinal and altitudinal gradients. The length of the photoperiod varies markedly along a latitudinal gradient but is not affected by altitude; thus, if length of photoperiod affects an organism this effect will be related to latitude but independent of altitude. The other difference between altitudinal and latitudinal gradients is in solar radia- tion. The intensity of different portions of the solar spectrum is modified by the thickness and composition of the atmosphere penetrated (Gates, 1962). In particular, sunlight at high altitudes is richer in ultraviolet light than at lower elevations.

It is possible that this greater intensity of ultraviolet light at high elevations has some significance for insect life but we do not know that this is the case.

As previously implied, the faunas of high altitudes and high latitudes have pronounced similarities but differ in certain respects. Their similarities are evident when we note the boreal affinities of most of the species composing the high altitude biota. Their differences include, particularly, the occurrence of many more accidentals- wanderers at high altitudes than in high latitudes (G. Alexander, 1964). This is simply because the distance from the normal range is much less in mountains than along a latitudinal gradient.

All differences between the effects of altitude and latitude require that one eliminate latitude as a factor when considering altitude as the variable. Studies of altitude should therefore be made along an east-west altitudinal gradient in a relatively narrow band of latitude. Such a gradient is available in the mountains near Boulder, Colorado, and it was its availability that prompted the beginning and continuation of this study.

DESCRIPTION OF REGION

GENERAL ACCOUNT

The Front Range of the Rocky Mountains of northern Colorado trends almost due north and south. It thus provides an east-west gradient of altitude in which studies can be restricted to narrow latitudinal bands. The altitudinal gradient near Boulder extends over a vertical range of more than 9,000 ft (about 3,000 m), with the highest elevations no more than 30 miles from the lowest. The region is thus ideal, topographically, for the study of altitude as a factor in animal distribution. It also has other major advantages for our study. Botanists and zoologists, geologists and meteor- ologists, have been working in the area for many years. Some have been interested in the effects of altitude, and their studies have been particularly useful in providing general background material.

The region of our intensive study lies around and to the west of Boulder. It is all included on the U. S. Geological Survey map called the "Denver Mountain Area" (No. N3930-W10445/ 75x75). This map, which is a composite of U.S.G.S. quadrangles, with 500-ft contour intervals, provided the basis for our map, Fig. 1, on which one can locate most of our frequently used collecting stations.

To reduce latitudinal variation to a minimum we concentrated our collecting in a band along the 40th Parallel, North Latitude. This parallel




Aft Rocky M at < 0 5?~105 30' W 101

S

1W

Rocky Mountain Nat~ional Pr

4 0 7 1'aN.

9 P ~~~~~~Roii~sviiie ? ,r9 g% Lafayett 39000/eN.

12,000ft abovessea level. Tht e area0 b~detweenr10,000 and 12,000fdt is indicated b000

Winter ( oisil

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~~~~~~~~Mount ~~~~~~~~~~~~~~~~~39*521aN. V- V ~~~va ~Denveir

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FIG. 1. Map of the Boulder region. Contour intervals shown are 5,000 ft, 6,000 ft, 8,000 ft, 10,000 ft, and 12,000 ft above sea level. The area between 10,000 and 12,000 ft is indicated by stippling; that above 12,000 ft, by hatching. The weather stations of the Institute for Arctic and Apline Research are located by the symbols A-1 (7,200 ft), B-1 (8,500 ft, C-1 (10,000 ft), and D-1 (12,300 ft). All regularly visited stations, except those on Mt. Evans, were between 39? 52' 30"N. and 40? 7' 30" N.

intersects Boulder. Most collections were made in a band between 390 52' 30" North and 400 7' 30" North, on the east side of the Continental Divide, from an altitude of approximately 5,000 ft (1,530 m) above sea level, on the east (at approximately 1050 14' West Longitude), to over 12,000 ft (3,660 m), on the west. The most western collections in this band were at about 1050 45' West Longitude. The north-south width of this area (15' latitude, about 16 miles) introduces a latitudinal variable corresponding, under average conditions, to a difference of only 100 ft in altitude (Hopkins, 1919).

Although there are six peaks in excess of 13,000 ft (about 4,000 m) within our area these can be reached only by hours of climbing on foot. Some of our records from above 12,000 ft did come from these mountains, but most of them are from Mount Evans, whose summit is about 20 miles south of the southern edge of our area and several miles east of the Continental Divide. An excellent road on Mount Evans makes elevations all the way to its summit, 14,260 ft above sea level (4,348 m), readily accessible. In our RECORDS OF INDIVIDUAL

SPECIES we include all records from the Mount Evans area as well as from the more restricted latitudinal band. (The maximum north-south width of the area from which collections are tabu-

lated is thus 36 miles, which introduces a latitudinal variable less than the difference between north and south exposures at the same altitude.) We include a few records from Argentine Pass, 13,132 ft, a short distance west and north of Mount Evans. We mention, but do not include in our generalizations, a few records from Trail Ridge, which is about 20 miles north of our area, and which is in Rocky Mountain National Park.

Most of our collections were made on the eastern slope, but we did make collections at timber line on the western slope, between Rollins Pass and Winter Park, with fair regularity.

The increase in altitude from the plains immediately east of Boulder to the highest peaks on the Continental Divide to the west is at an average gradient of a little over 280 ft per mile (53 m per km). It is natural that this gradient should be fairly steep, for, along the northern edge of our area, the Continental Divide (at Sawtooth Moun- tain) is further east than anywhere else in the United States, and the high plains of Colorado extend further west than elsewhere in the state. The 5,000 ft contour and the summit of Sawtooth Mountain (12,304 ft) are only 26 miles apart.

We use English units (feet and miles) throughout in locating collecting stations and indicating altitudes above sea level. This is for two reasons:




These units, rather than those of the metric system, are used on the maps of the U. S. Geological Survey; and American biologists working in mountains (as well as American mountaineers) are accustomed to thinking in terms of these and not the metric units. We see no significant trend toward a change in this practice.

Fig. 2 summarizes July and annual mean temperatures and the mean lengths of the frost-free season along our altitudinal gradient. The data used are from five weather stations, one at Boulder and four at the mountain stations established and serviced by the Institute of Arctic and Alpine Re- search of the University of Colorado. (Their lo- lations are indicated in Fig. 1.) We are particularly fortunate in having these figures; such comprehensive weather data recorded for so many years along an extensive altitudinal gradient are probably not available anywhere else in the world.

Temperature variables are, for insects, probably the most significant climatic variables related to altitude. From the same locations and sources providing the data in Fig. 2 we also have, however, figures on mean annual precipitation in inches (Boulder, 18.18; A-1, 20.96; B-1, 21.19; C-1, 25.85; D-1, 25.22). The figure from D-1, owing to the difficulty of measuring precipitation during continuous high winds, should undoubtedly be higher. (Mean wind velocity, as well as precipitation, increases with altitude-on the tundra aver- aging 10 miles/hr in mid-summer and 25 miles/hr in mid-winter.) Paddock's (1964) account of the climate of the Boulder region, based primarily on

90

1700 C E V J 0 0 0 X W 0 -70

a 9O_ x ~~~~~~~~~~~~~- 6 0

_ _0_ 20

50 + + +

Boulder A-I B-I C-I D-l

. 6 7 8 9 10 I 12 Altitude In 103 f t

FIG. 2. Temperature gradients in the Boulder region in relation to altitude. Solid lines: J = mean temperatures for July; A = annual mean temperatures. (The vertical lines indicate the range between the means of daily maxima in July and the means of daily minima.) Broken line: Number of consecutive days above 320 F. All data are means for the years 1953-1964, omitting 1956. (Data for 1956 were omitted since some of the records for that year were incomplete.) Data for A-1, B-1, C-1, and D-1 from Marr et al. (1968) and for Boulder from U. S. Department of Commerce, Weather Bureau (1953- 1964).

records of the Institute, is an excellent general summary.

Soil surface temperatures, which are highly variable-especially so at high altitudes-are perhaps of more immediate significance for insects than are air temperatures, but we have no comprehensive data on these, and air temperatures do suggest the general climatic pattern. The Insti- tute records include observations on soil temperatures-at depths of 5 inches and more, however. Gregg (1963) discusses soil temperatures and the effects of slope exposure in our area, and his book should be referred to for a discussion of features of the Colorado climate of particular significance for insects.

The four mountain weather stations of the Insti- tute are all ridge-top stations, and all are in our restricted area. Their names and elevations are: A-1 (7,200 ft), B-1 (8,500 ft), C-1 (10,000 ft), D-1 (12,300 ft). Stations A-1, B-i, and C-1 are in clearings in the forest, C-1 being in a larger clearing than either of the others. Station D-1 is in the alpine tundra near the west end of Niwot Ridge. The three lower mountain stations were frequently visited as collecting sites on our project, but the highest station was visited only occasionally. None of the four was readily accessible without a 4-wheel drive vehicle.

We shall here give only a brief account of the biotic gradient along our altitudinal transect, and we shall describe our collecting sites in the next section. Marr (1961) described in detail the vege- tational changes correlated with altitude in the Boulder region; and Gregg (1963) gave a comprehensive summary of the various classifications of altitudinal biotic zones throughout Colorado.

The lower limit of the forested portion of the mountains near Boulder is at approximately 5,800 ft (1,900 m) above sea level. Below this altitude trees occur naturally only along watercourses, and the dominant natural vegetation is of mixed grasses and forbs. Plains collecting stations were selected for variety of natural vegetation-in order to obtain the maximum variety of Orthoptera. (Grain and hay fields may be infested with grasshoppers periodically but only a few species are present in such places, and such fields do not provide a sample of the characteristic fauna of the area.)

The mountains are forested from lower timber line to an upper timber line at about 11,000 ft (3,600 m). This upper timber line, hereafter meant when the expression "timber line" is used, is somewhat higher on south-facing slopes and lower on north-facing slopes, this difference being more than 500 ft. The dominant trees at lower



390 GORDON ALEXANDER AND JOIIN R. HILLIARD, JR. Ecological Monographs i ~~~~~~~~~~~V ol. 3 9, N\To. 4

altitudes are ponderosa pine and Douglas fir, the former in open forest on drier exposures, the Douglas fir chiefly in dense stands in more moist areas. These trees occur up to over 9,000 ft, but a species more abundant than either at intermediate elevations (8,000 to 9,000 ft) in our area is lodgepole pine (Moir, 1969). The subalpine forest, which is moist forest, is primarily subalpine fir and Engelmann spruce. Both of these trees occur in stream bottoms at elevations below 9,000 ft, but the subalpine forest is predominant above 10,000 ft. Limber pine and quaking aspen form important stands under local conditions, and foxtail pine occurs as far north as Mount Evans, where it is prominent at and below timber line.

No Orthoptera are associated with particular species of trees, nor are many individuals to be found in forested areas, yet there are species limited to this forested region of the mountains. The Orthoptera of these intermediate elevations occur primarily in clearings, natural or artificial, in the forest. Our collecting stations were all in clearings, our sampling including the adjacent forest borders.

The alpine tundra is of low grasses, sedges, and forbs. Although only a few species of Orthoptera are characteristic of the region, numbers of individuals may be large. It seems likely that climatic rather than biotic factors are the major limiting factors in the complexity of the resident fauna for several species occur regularly as accidentals but are unable to complete their life cycles (G. Alex- ander, 1964).

COLLECTING STATIONS

Although data from collections and observations during a period of more than 30 years are incorporated in this paper, the most valuable studies were made during the four seasons, 1949', 1958, 1959, and 1960. During these years selected collecting stations over a wide range of altitude, but all near the 40th Parallel, were visited regularly. This procedure gave us a more consistent picture, both of altitudinal ranges and seasonal occurrence, than other types of observations, and most of the data here summarized are from these seasons. Observations during other years have contributed mainly to rounding out the record, particularly filling in gaps in information about scarce species.

The stations visited regularly were at locations where previous experience had shown us we could expect a maximum or near maximum variety of Orthoptera for a-given altitude. Such stations are (1) open J.e., exposed to sunlight much of the day; (2) they have a large variety of herbaceous

vegetation; and (3) they are on approximately horizontal or south-facing--but not steep-terrain.

Because the most elaborate program was carried out during 1958 to 1960, inclusive, the stations used during those seasons yielded more data than either earlier or more recent studies. We describe these stations here in some detail, then refer to them later by symbols. The symbols consist of a number and a letter for each station, the number referring to an altitudinal range, the letter to a specific station within that range. Numbers 1 to 5 have the following altitudinal equivalents: 1, stations below 6,000 ft (in the plains zone) ; 2, stations from 6,000 to 7,500 ft (lower montane) ; 3, stations from 7,500 to 9,500 ft (upper montane); 4, stations 9,500 ft to timber line, approximately 11,000 ft (subalpine) ; 5, stations above timber line (alpine). Collections made at the same stations in other years are referred to by the same symbols. Stations used less frequently are identified by location and altitude.

During the seasons 1949 and 1958-1960, stations were visited regularly to acquire the seasonal picture. In 1949, visits by the senior author, usually alone, were made to a series of stations from 5,150 ft to 11,000 ft at biweekly intervals. In the seasons 1958-1960, inclusive, the collections were made by 3 to 5 individuals on each trip, at intervals of about one week at stations below timber line and at approximately biweekly intervals above timber line-though trips above timber line were divided between Mount Evans and the Rollins Pass area. Since the field season begins progressively later at higher altitudes there were fewer collections from the higher elevations. Dur- ing these three seasons collections were made with consistency, though with some year to year changes, at the 14 stations listed in Table 1. Note that 3 of these were below 6,000 ft, 2 between 6,000, and 7,500 ft. 2 between 7,500 and 9,500 ft, 3 between 9,500 ft and timber line (including 2 in the timber line ecotone), and 4 above timber line. Not all stations were visited on each trip but stations in every altitudinal band were.

The total number of collecting trips varied from year to year. It is apparent from examination of Table 1, however, that the proportion of trips made to selected collecting stations increased markedly during the second and third seasons. Less than half the collections in 1958 were made at these 14 stations, but in 1959 approximately 70%o and in 1960 over 80% of the collections were at these stations. This is due, of course, in part to the fact that 1958 was an "apprentice" year for the program, a year in which we learned from experience where we could most profitably spend our time.




TABLE 1. Collecting stations visited regularly during the seasons 1958-1960, inclusive.

Number of Station Altitude Collections

Symbol Name (Ft) 1958 1959 1960

la Pasture south of Boulder 5,450 7 19 25 lb Valmont Butte 5,150 10 16 4 IC Chautauqua Mesa 5,750 5 14 28 2a Chicken Ranch Gulch 6,700 8 20 23 2b A-1 Weather Station 7,200 4 15 2 3a B-1 Weather Station 8,500 2 15 0 3b Meadow west of B-1 8,500 1 15 20 4a C-1 Weather Station 10000 4 15 14 4b Timber line, Mt. Evans road 11,500 1 3 4 4c East timber line, Rollins Pass road 11,200 1 4 3 5a Near Goliath Peak, Mt. Evans road 12,100 1 6 4 5b Summit Lake, Mt. Evans 12,800 2 6 4 5c Upper saddle area, Mt. Evans 13,100 1 6 3 5d Rollins Pass 11,700 1 4 2

Number of collections at above stations 48 158 136

Total collections including other localities 123 231 172

Collections in 1959 were the largest. The distribution of 1959 collections from seven of the most important stations, tabulated in numbers of species and individuals, is summarized in Table 2.

Three of the stations regularly visited in 1949 correspond with Stations lb, ic, and 2a of 1958- 1960. One additional plains station used in 1949 was a pasture at 5,450 ft, 4 miles north of Boulder. This was similar to la, but its vegetation was more sparse, from grazing. It will be referred to as "pasture north of Boulder." There were two montane stations in addition to 2a, the lower in an open basin at 7,600 ft, on the Sunshine Canyon road northwest of Boulder. This was surrounded by ponderosa pine, and its vegetation was similar to that of Station 2b. It is our "Sunshine Canyon at 7,600 ft." The upper montane station in 1949 was on a south-facing hillside at 8,500 ft, immediately north of Nederland. It was in clearings in ponderosa and lodgepole pine. This is referred to later as "hillside north of Nederland, 8,500 ft."

The only area above timber line visited regularly in 1949 was at 11,000 ft on Baldy, the eastern prolongation of Arapahoe Mountain. (Not "Bald Mountain" of topographic maps; that is locally called Niwot Ridge.) This site was in the lower edge of the alpine tundra, and it required a long climb on foot from the nearest road. All other collecting stations were near roads. All 1949 collections were made by the senior author, occasionally with the assistance of his wife, Marion I. Alexander, his son, Douglas G. Alexander, or H. A. Fehlmann or P. A. Buscemi.

In the following descriptions of the stations used during 1958-1960 we have not listed plant species in detail. We have, however, listed those plants whose presence is correlated with the occurrence of certain species of Orthoptera. Most species of grasshoppers feed on a variety of plants, usually concentrating on either forbs or grasses, but a few are relatively limited in food usage (Isely, 1946; Anderson, 1964). Our descriptions of specific collecting stations are rather general, therefore, except in detailing plant species correlated or apparently correlated with the occurrence of particular species of Orthoptera.

Station la. Pasture south of Boulder. This area, 2 miles south of the National Bureau of Standards Laboratory and at an elevation of 5,450' ft, was ungrazed, mixed pasture from 1958 through 1962 (Fig. 3). Here we found the greatest variety of Orthoptera of any station, 52 species during 1958-1960, of which 33 were taken in a single- collection. This pasture has recently been ab- sorbed by an expanding residential area and a school, so our description is necessarily in the past tense.

The soil was a dark brown, shallow, friable loam, with rocks and boulders strewn throughout the surface layers. Low shrubby clumps of Helian- thus purnilus Nutt., and Ceanothus herbaceous Raf., were interspersed with a heavy growth of

TABLE 2. Summary of 1959 collections from seven major stations. The last two columns give the maximum number of species and the maximum number of individuals in a single collection (not necessarily the same collection) during the 1959 season.

Season Single Collection

Number Number Number Maximum Maximum Altitude of of of Number Number

Station (Ft) Collections Species Individuals Species Individuals

la ............ 5,450 19 45 4,847 33 571 lc ............ 5,750 14 37 1,890 24 223 2a ............ 6,700 19 40 4,621 24 703 3b ............ 8,500 15 25 1,973 17 298 4a ............ 10,000 15 16 1,335 12 186 4c ............... 11,200 4 8 587 8 254 5b ............ 12,800 6 4 846 4 179



392 GORDON ALEXANDER AND JOHN R. HILLIARD, JR. Vogl.M39, go.h

FIG. 3. Station la. Pasture at an elevation of 5,450 ft, south of Boulder, ungrazed from 1958 through 1962, now the center of a building development. Late season aspect.

forbs and grasses. (From here on, scientific names of plants will be accompanied by author names only when they first appear, the names conforming with Weber's 1967 treatment of the regional flora.)

A seasonal change from a lush growth of soft forage in late spring and early summer to a more xeric, coarse forage in late summer and fall took place. Among the forbs of special significance early in the season were Phacelia heterophylla Pursh and several composites, including Helian- thus pumilus. Later, in addition to composites, Artemisia ludoviciana Nutt., and Ambrosia psilo- stachya DC., were prominent. Several grasses were present, Bromus tectorum L., being dominant, especially late in the season.

Station lb. Valmont Butte. The Butte is a volcanic dike, with an east-west trend, about 4 miles east of Boulder. It reaches an elevation of 5,300 ft. rising some 190 ft above the surrounding plain. Our collecting area was on the south side, the steepest part with a slope of about 30 degrees. We sampled an area about 200 yards long, extending a little over half way up the slope from the base.

The slope is strewn with dark basalt rocks, but the surface of the soil is weathered shale, decom- posed to form a fine clay soil. The west end of the Butte is being cut away, and it has been used for many years in the manufacture of bricks by the Colorado Brick Company. At the east end of the Butte, about a quarter mile from the clay excavation, is the Valmont Mill of the Allied Chemical Company, which mills fluorspar ore trucked in from Jamestown, Colorado. The slope has an old roadway and ditch traversing the middle, lengthwise, a new roadway near the mill, and a ditch along the lower edge that drains water

from the mill. Dust from the mill operation forms a thin coating on the vegetation. Reduction in the complexity of the vegetation has occurred since 1937, when the mill was established, and the variety of Orthoptera present today is much less than in the early 1930's. We have visited the Butte in recent years primarily because it provides, with its south-facing slope, early season records for the species that do occur.

This south-facing slope supports a xeric vegetation of grasses, cactus, yucca, and other forbs. On the steeper part, the predominant plant is the grass, Bromus, tectorum. Also common on the slope is Lactuca scariola L., and there are other forbs. Common along the roadway is Russian thistle, Salsola kali L., and on bare dry areas Kochia iranica Bornmueller occurs. At the base of the slope, along the ditch, a more mesic growth of grasses and forbs occurs.

Station 1c. Chautauqua Mesa. This is our name for a large grassy meadow between the Chautauqua grounds, in the southwestern edge of Boulder, and the entrance to Gregory Canyon to the west. It is the northeast-facing slope of the first mesa south of Boulder, with a slope averag- ing no more than about 5 degrees in the collecting area (Fig. 4). It is about 5,750 ft above sea level, and is a mesic, bluegrass meadow, strewn with large rocks and boulders. It is our highest station representative of the grassland formation, but since it is near the lower edge of the coniferous forest its fauna has the characteristics of an ecotone. Some plains species of Orthoptera reach their highest altitude here, while several montane species are at their lowest limit.

The vegetation is of grasses and forbs, with scattered clusters of low shrubby choke cherry, Prunus virginiana L., and sumac, Rhus glabra

I~~~~~~~~~ /

_,ii_~~~A .

FIG. 4. Station 1c. Chautauqua Mesa, elevation 5,750 ft. Our highest station in grassland climax, its fauna ecotonal in character. The lower tree line (ponderosa pine) is in the background.




L. The dominant plant is Kentucky bluegrass, Poa pratensis L., and other grasses are present. Conspicuous forbs include Helianthus pumilus, Lactuca scariola, several members of the pea family, Artemisia ludoviciana, and others.

This area and the next station are parts of the Boulder City Parks System. These will, we hope, be protected from types of development that have eliminated from future research the stations previously described.

Station 2a. Chicken Ranch Gulch. This is a shallow valley in the lower montane zone (Fig. 5), at about 6,700 ft on the south side of Flagstaff Mountain, a small mountain in the Boulder Parks System. The station is near the road that goes up the mountain. A small, intermittent, spring brook, Gregory Creek, flows through the area. The gently sloping north side of the Gulch (with a 10 to 15

FIG. 5. Station 2a. Chicken Ranch Gulch. A small grassy valley at 6,700 ft. Mixed herbaceous vegetation surrounded by ponderosa pine and Douglas fir.

degree slope toward the south) is an open grassy meadow, with small open spaces among scattered ponderosa pine, Pinus ponderosa Laws. The valley floor is wide and gently rolling, with scattered moist swales near the creek. The steeper south and west sides of the Gulch are densely wooded with ponderosa pine and Douglas fir, Pseudotsuga menziesii (Mirb.) Franco. The soil of the slope is a shallow, coarse, sandy loam; that of the floor of the valley is a deeper, fine grained sandy loam.

A lush growth of sedges, grasses, and horse- tails occurs along the stream. Shrubby growths of willow, cottonwood, and alder form thickets near the creek. Forbs in the Gulch include several composites-Grindelia squarrosa (Pursh) Dunal, Helianthus pumilus, Taraxacum ofiicinale Wig- gars, and others, several legumes, Artemisia ludoviciana, and others. Among several conspicuous species of grasses are Poa pratensis and Agropyron smithii Rydb.

Station 2b. A-1 Weather Station. This collecting station is adjacent to the A-1 weather station of the Institute of Arctic and Alpine Research. It is on a ridge top, with adjacent south-facing slope, at 7,200 ft, in an area lumbered heavily about 90 years ago. The plant ecology has been carefully studied by John W. Marr and others of the Insti- tute staff. Our collecting station comprises what Marr (1961) refers to as Stands A-1 and A-3, both including some open area and meadows in ponderosa pine forest and A-3 being on the south- facing slope. We visited this station regularly in 1959 but only a few times in 1958 and 1960; its orthopteran fauna is similar to that of our Sta- tion 2a.

Station 3a. B-1 Weather Station. Our Station 3a is a relatively flat, rocky, ridge top area, adjacent to weather station B-1 and in Stand B-1 of Marr (1961). It is about a half-mile west of Sugarloaf Mountain and at an elevation of 8,500 ft. The soil over most of the area is a coarse sandy loam. The trees are ponderosa pine, Doug- las fir, and low spreading juniper, Juniperus communis L. We did not visit this station after 1959 because Station 3b, at the same altitude and not far from Station 3a, proved to be more suitable for our purpose.

Station 3b. Meadow west of B-i. This meadow is located at the same elevation as Station 3a, one and a half miles west of B-1 weather station. The area is accessible by a dirt road that follows the grade of the abandoned narrow-guage railway west of Sugarloaf. The collecting location is an expansive open meadow, with parklike areas in predominantly ponderosa pine forest, sloping grad- ually toward the southeast (Fig. 6). The soil of the meadow is a deep, well developed, fine sandy loam; it supports a predominantly grassy vegetation but has numerous conspicuous species of forbs as well. Station 3b was of particular value

- ~~~~~~~~~~~~V

4~~~~~~~~~~~

FIG. 6. Station 3b. Meadow in a park-like open area at 8,500 ft altitude. Mixed herbaceous vegetation with scattered shrubs on southeast-facing slope. The area is much more extensive than indicated in this photograph.



394 GORDON ALEXANDER AND JOHN R. HILLIARD, JR. Ecological Monographs

FIG. 7. Station 4a. The clearing immediately around Weather Station C-1. Elevation 10,000 ft. The trees are lodgepole pine and aspen. The eastern end of Niwot Ridge, in the background, carries alpine tundra further east than elsewhere in the region.

to us as it was the most extensive open area we sampled between 6,000 ft and timber line.

Station 4a. C-i Weather Station. Our Station 4a is adjacent to weather station C-1 of the Insti- tute of Arctic and Alpine Research and in Stand C-1 (Fig. 7) as designated by Marr (1961). It is on top of an extensive glacial moraine immediately west of and above Science Lodge of the University of Colorado and on property owned l y the University. It is in the subalpine forest region, on the site of a former lumber camp, Hill's Mill, at an elevation of 10,000 ft. The area is relatively open; numerous stumps attest to the lumbering operations of the past, discontinued about 1900.

The most numerous tree is lodgepole pine, Pinus cortorta Dougl., but stands of aspen, Populus tremuloides Michx., subalpine fir, Abies lasiocarpa (Hook.) Nutt., and limber pine, Pinus flexilis James, are also present. The soil is a rocky glacial till, described by Marr (1961) as "a podzol with an orange-brown colored B. horizon." Vaccinium myrtillus L., is present in the area, as well as a number of herbs, including Thermopsis divari- carpa Nels., species of Potentilla and Sedum, and sedges and grasses.

Station 4b. Timber line on the Mt. Evans road. Because of the presence of a paved highway to the summit of Mt. Evans, the road being open from June through September, several collecting stations were selected along this highway-at altitudes from the subalpine-alpine ecotone at timber line (11,500 ft) to above 13,000 ft. The timber line collecting station (Fig. 8) has a southeast exposure. The area is rocky; the soil is a light yellowish, gravelly clay. Wind rows of large, contorted, flag trees of bristlecone pine, Pinus

vegetaion. - ~~~~~~~~~~~-10

yWIW

Fic 8 Station 4b. Timber line on the Mt. Evans road, 11,500 ft. The trees are bristlecone pines (Pinus aristata). Scars left during highway construction are still extensive, considerably reducing the areas of natural vegetation.

aristata Engelni., dominate the area. Dwarf willow and shrubby cinquefoil are present, with about 50% of the vegetative cover dwarf willow. The principal grass is hair grass, Deschamn/sia caespitosa (L.) Beauv. Also present are small clumps of Carex rupestris All. Forbs in the area include Trifolium nanum Torr., and Geum rossii (R. Br.) Ser., as well as species of Sedum, Cirsium, Phacelia, Senecio, and other genera.

Collections were less numerous here than higher up on Mt. Evans. We usually began our collections at the highest altitudes and worked down, and on several occasions the more or less regular afternoon storms made collecting at timber line impossible. Our timber line analyses are based chiefly on collections from Station 4c.

Station 4c. East timber line, Rollins Pass road. The Rollins Pass road is a dirt road that follows the grade used by the railway before completion of the Moffat Tunnel in 1927. It is passable in summer trom Tolland, across the mountains, to Winter Park, but is usually blocked by snow just below timber line until the second week of July. It crosses the Continental Divide at Rollins Pass (11,700 ft) at the southwest corner of Boulder County, this pass locally called Corona Pass- after the small railway town, Corona, formerly at the Pass.

Station 4c is a timber line, subalpine forest-alpine tundra ecotone area at about 11,200 ft (Fig. 9). The soil is a coarse sandy loam among large rocks and boulders; it supports a grassy tundra of grasses, sedges, and mixed forbs (Fig. 10). The most common grasses include Poa alpina L., and Calamogrostis purpurescens R. Br., and Carex rupestris is the common sedge. Conspicuous forbs include Geum rossii, Dryas octopetala L.,




.j5

FIG. 9. Station 4c. Timber line on the east side of Rollins Pass as seen from the north. Tree line is in- definite, characterized by scattered tree islands extending above our collecting station-which was on both sides of the road near the center of the area in this photograph.

le ct

FIG. 10. Station 4c. Tundra vegetation at timber lIne (11,200 ft) on the east side of Rollins Pass. Mid-season aspect. The fauna is ecotonal; for example, Melanoplus dodgei and M. borealis are both here, as are Aerope- dellus clavatus and Chorthippus curtipennis.

Bistorta bistortoides (Pursh) Small, Silene aca t- lis L., and species of Phacelia, Cirsium, Trifoliunt, Erigeron, Cerastium, Antennaria, Potenti!I., and other genera.

Station 5a. Near Goliath Peak, M. Evans roal. This station is on an east-facing slope immzdiately below a parking area in the saddle three-fouiths mile south of Goliath Peak (Fig. 11). It is in rocky, relatively dry tundra at 12,100 ft, the vegetation being mixed herbs. Boulders up to 6 ft in diameter are strewn over the slope, which is about 10% and toward the east. The soil is a coarse sandy loam-spongy, with a rich dark humus content-and is especially well developed where protected from erosion by boulders. Coarse sand occurs on the open surface, but a fine gra'ned dark loamy soil is present in the tussocks. Alout 15%o of the site is bare ground, and the vegetation is about 50% grass-sedge and about 50% forbs.

- ;~~~~~-A

FIC. 11. Station Sa. This tundra station, at 12,100 ft on the Mt. Evans road, had a mixture of grasses and forbs among the rocks. (Goliath Peak is the ridge in the immediate left background. The Pesman nature trail of the Colorado Horticulture Society begins in this area.) Aeropedellus clavatuts, Melanwoplus dodgei, and Anabrus simplex all have well established populations here.

The most common grass is Descharnpsia caespitosa, and the most common sedge, Carex rupestris. The most abundant forbs are Geum rossii and Bistorla bistortoides, but several others are common.

Station 5b. Surniin.t Lake, Mt. Evans. This station is located immediately northeast of Summit Lake, at an elevation of 12,800 ft (Fig. 12). The area consists of a gently rolling, rocky meadow, with both wet and dry tundra vegetation. Large boulders occur through the area, with the tundra continuous around them. A wet tundra community of sedges, Pedicularis groenlandica Retz., sedums, and other herbs flourishes around pools of water around the rocks and in the marshy seepage areas of solifluction terraces. The drier areas support a lush growth of Geum rossii and Bis-

FIG. 12. Station 5b. The tundra near Summit Lake, Mt. Evans, at 12,800 ft. Late season aspect. A more comprehensive view of the area, in late June, appeared in our 1964 paper. Aeropedellus clavatus is well established here, Anabrus simplex is moderately common, and AMelanoplus dodgei is present but scarce.



396 GORDON ALEXANDER AND JOHN R. HILLIARD, JR. EcoIa Monogph

torta bistortoides; Hymenoxys grandiflora (Pursh) Parker and other forbs occur.

Station Sc. Upper saddle area, Mt. Evans. This is southeast of the summit of Mt. Evans, in the saddle between Mt. Evans and Epaulet Moun- tain, at an elevation of 13,100 ft (Fig. 13). It is characterized by large boulders and discontinuous tundra vegetation (Fig. 14). Extensive patches dominated by tussocks of Carex rupestris indicate that this is a wind-swept area, free from snow during much of the winter, and this sedge is the predominant plant. The tundra is discontinuous; it varies from 50% bare ground to places where tussocks form a continuous cover over a square meter in extent. In some parts of the area grasses and sedges predominate, but there are several species of alpine forbs as well.

Station Sd. Rollins Pass. This pass is in the alpine tundra at an elevation of 11,700 ft (Fig. 15). Our collecting site, immediately north of the Pass, consisted of hairgrass meadows and areas disturbed by the activity of pocket gophers. The soil is a sandy loam, and it is rocky. Forbs, chiefly

U- FIG. 13. The saddle area on Mt. Evans (Station Sc)

as seen from above, looking toward the southeast.

-U~.- A.'

FIG. 14. Closeup view of Station 5c, 13,100 ft in altitude. Clumps of predominantly grassy vegetation amid rocks shelter a well established population of Aeropedellus clavatus and a few Anabrus simplex.

-I. FIG. 15. Station 5d. Rollins Pass, elevation 11,700 ft.

Here Melkanoplus marshalli, extending up into the tundra from the west side of the range, reaches its upper limit late in the season. Aeropedellus is well established- and earlier in the season.

Bistorta bistortoides and Geum rossii, form the dominant vegetation in areas of gopher activity. Grassy stands develop in less disturbed areas; there, Deschampsia caespitosa is the most common grass.

NATURE OF OBSERVATIONS

Most specimens that served as a basis for this report are from collections made by the senior author and his associates over more than 30 seasons. Appropriate records from other sources, where significant for this study, have also been incorporated-with corresponding credit.

During 1949, 1958, 1959, and 1960, the seasons of intensive, regular collecting at definite stations, over 65,000 specimens of Orthoptera were collected, identified, and recorded by date, altitude, and locality. For each adult specimen the sex was also recorded. Most juveniles collected during the 3 year period, 1958-1960, were identified to species and by age (instar). In many cases the sex of juveniles was also determined.

Identification of early instars became possible in most species by comparing earlier with later stages. Fifth instar juveniles usually look much like adults of the same species and are readily identified. (Species-characteristic features of the external genitalia of males are evident by that stage-a condition particularly helpful in identifying juvenile specimens of species of Melanoplus.) By matching each earlier stage with the appropriate succeeding stage it has been possible to identify most species at stages at least as early as the third instar. Some species were reared from early stages. It is particularly important to identify juveniles of long-winged species; we can be sure that such species are resident at a given altitude




only when we find juveniles (and therefore flightless) stages. For characteristics of the different instars see Shotwell's 1941 paper.

In some cases, laboratory tests of feeding were carried out, using plant species collected in the habitat in which the orthopteran occurred. Foods taken were determined in some cases by crop analysis (Isely & Alexander, 1949). The junior author, who had previously made special studies of food preference (Hilliard, 1950), made the food determinations. We supplemented these observations with data from Gangwere's (1961) summary of the food habits of Orthoptera and from other sources, cited where appropriate. (Mulkern's 1967 discussion considers the principles of food selection by grasshoppers.)

Not all specimens were preserved. Many dupli- cate specimens of common species were discarded, after tabulation, in order to save storage space, but one or more specimens of each species from each collection were saved-to validate records. All specimens of certain montane and alpine species, which are being used for further studies of populations, have been preserved.

The completeness of the sampling may be judged from the fact that we collected over 28,000 specimens in the Boulder area in 1959 without finding a single species that had not been previously collected there. Such comprehensive sampling of species, combined with the recording of all individuals collected, gives us a basis for comparing the abundance of different species, too.

Needless to say, most of the Orthoptera collected were Acrididae. Tettigoniidae and Gryllidae are not well represented locally, being more abundant in warm, moist regions-though a few species of the former have become adapted even to high altitudes. Many species of these families are noc- turnal, and night temperatures at high altitudes, even when day temperatures are fairly high, may be too low for these forms. Furthermore, our methods were not adapted for adequate sampling of, particularly, the ground-dwelling Gryllidae and Gryllacrididae. We believe our sampling has been quite adequate, however, for all Orthoptera active in the vegetation above ground level, and our generalizations have been based on these.

Our method of sampling was intended, primarily, to be qualitatively exhaustive, for we were interested mainly in obtaining a complete taxonomic and age sample. The collector or collectors (usually 3 to 5 experienced collectors) spent about 30 min working carefully with sweep, nets. Addi- tional time was then given to capturing specimens that were too active or that kept too close to the ground to be readily taken in sweeping. The total

time spent at each station was approximately 45 mins-this being the average time necessary to obtain essentially complete representation. While primarily qualitative, this method proved also to be quasi-quantitative. Experience convinced us that we obtained most if not all species present at a given station in this amount of time, that these were approximately proportional in our collection to relative numbers at the station, and that age groups were well represented-these too in approximately relative numbers. It was thus possible to consider not only altitudinal limits of species but their relative abundance at different altitudes and the times for different events in their life histories.

We have long known that counting sweeps as a basis for quantitative data is deceptively unre- liable, as has been pointed out by several insect ecologists (e.g., Cantrall, 1943; Dreux, 1962). It is not applicable for collections of mixed species, or in different habitats to be compared, or when several collectors with varying skills are involved. Our substitution of time for number of sweeps, supplemented by other methods of collection aimed at obtaining a taxonomically complete sample, has served our purpose well. It has provided us with collections indicating relative numbers of species and age groups if not their absolute densities.

Identifications were made by the authors. Dur- ing 1958, 1959, and 1960, the junior author made most of the determinations of juveniles. Our assistants on the project often carried out routine identifications, making use of keys prepared for Colorado species (G. Alexander, 1941); but after the specimens from a given collection were sorted, tentatively identified, and counted, the identifications were confirmed by one of the authors.

We raise few questions here of a taxonomic nature. For that reason, we do not pursue certain problems that may involve recognition of sub- specific or specific distinctions among populations here considered taxonomically the same. The nomenclature used is that of Hebard (1929) as modified by his later papers and by those of others working with specific groups. We cite specific taxonomic literature, where appropriate, in con- nection with particular species or groups of species. The guide recently prepared by Helfer (1963) will be found quite useful, both in identification of species and for its general information on distribution and habits.

RECORDS OF INDIVIDUAL SPECIES

INTRODUCTION

Ninety-five species of Orthoptera and orthopteroid insects, arranged in major taxonomic




groups, are included in the following account. For groups with small numbers of species the discus- sions are brief and general. Within the Acrididae, however, they are treated by subfamilies (those recognized by Uvarov, 1966a), and the species accounts for the three largest subfamilies have been further subdivided into: (1) those found on the plains only, (2) those found both on the plains and in the mountains, and (3) those limited to the mountains. Under each group, whether family, subfamily, or altitudinal category, the species accounts appear in alphabetic sequence.

Species accounts are of two kinds. For the 36 most common species of Acrididae (based on our 1958-1960 collections) they are somewhat detailed, including special biotic relations, seasonal occurrence and life history observations at different altitudes, and comments on latitudinal distribution. These accounts also give numbers of specimens collected (in our limited transect plus Mt. Evans) during 1958-1960. For the 59 less common species our accounts are shorter, but they do incorporate any observations of ecological significance.

Adult grasshoppers of fully-winged species are often strong fliers and may appear as accidentals at altitudes either higher or lower than their normal range. It is important that such vagrants (accidentals) be distinguished from established species (residents). The criteria for making such distinction have already been summarized (G. Alexander, 1964). Accidentals and residents have been distinguished in the following accounts.

NON-SALTATORIAL ORTHOPTEROID GROUPS

We have no records of Grylloblattidae in Colo- rado, but there is a remote possibility that Gryllo- blatta will eventually be discovered in the area. It occurs in the Rockies further north. Habitats that seem suitable occur between ten and eleven thousand feet, in places of winter snow accunu- lation and abundant summer moisture.

Two native species of Mantidae occur, but neither is common. The rarer of the two, Litaneu- tria minor (Scudder), appears to be restricted to the plains in our area, but it has been found at higher elevations both north and south of Boul- der. All our records are below 6,000 ft, and our dates for adults are from the first of August to the end of October. The smaller and somewhat more common mantid, Yersiniops solitarium (Scudder), occurs on the plains and in the foothills up to about 7,000 ft or a little higher. Col- lecting dates for adults are from the second week in August through October.

Only one species of Phasmidae is found in the

Boulder region, and it is uncommon. Adults of Parabacillus coloradus (Scudder) have been collected up to 6,700 ft, from the middle of August to the middle of October.

Our Mantidae and Phasmidae fit the general pattern of groups with a predominantly southern distribution: 1. They appear much later in the season than do forms with boreal affinities. 2. They are uncommon. 3. They are limited to lower elevations.

TETRIGIDAE

Grouse locusts are somewhat restricted in habitat, being usually associated with stream or lake margins and seepage areas. Members of the family are only locally common in our region, probably because suitable habitats are not abundant. Though able to fly, they are not strong fliers; they tend to remain in their chosen habitat, so we have assumed that they are resident where collected. Our collections from the plains would have been more extensive had we visited appropriate habitats more frequently, but we do have good samples from the mountains.

We collected four species of Tetrigidae, one with two subspecies. The nomenclature we follow is that of Rehn and Grant (1961). The genus Paratettix, somewhat southern in distribution, is represented in our collections only by a few specimens of P. cuculatus (Burmeister), all taken near Boulder Creek, east of Boulder, in mid-summer. We found four forms of Tetrix in our area- three species, one represented by two subspecies: T. brunneri Boliver, T. ornata ornata (Say), T. ornata hancocki (Morse), and T. subulata (Linn.).

Tetrix brunneri, which does not occur south of Colorado but ranges north into northern Canada and Alaska, is limited to fairly high altitudes in our region. Rehn and Grant (1956a) recorded it from 7,500 ft in Larimer County, immediately north of Boulder County, but our collections are all from 10,000 ft and above. We have taken it at 10,000 ft on the slope west of Rollins Pass (in Grand County), in our transect, and at Milner Pass (10,760 ft) in Rocky Mountain National Park, 18 miles north of our area, juveniles and adults at both places during the first half of August. All our specimens are brachynotal. Rehn and Grant (1956a, p. 101) suggested that brachynotal types may be better adapted for cold than are macronotal ones; certainly species and subspecies with predominantly northern distribution show a higher incidence of the former condition.

The two forms of Tetrix ornata, T. o. ornata and T. o. hancocki, overlap in altitudinal distribu- tioin according to the records of Rehn and Grant




(1956b), but we have not found this to be the case. We have taken T. o. hancocki only once in our area (juveniles, west of Nederland at about 9,600 ft, Aug. 9, 1961). We have repeatedly collected T. o. ornata: along Boulder Creek at 5,400 ft, in wet rush areas at Station 2a, and as high as 8,500 ft near Station 3a; adults as early as April 15 on the plains and April 30 at 7,000 ft, juveniles as late as mid-July. Of 26 specimens from our area, 19 are macronotal, but the brachynotal specimens are all from low altitudes, con- trary to expectation.

Tetrix smbulata was found from 6,000 to 10,000 ft in our transect. We did not take it on the plains but it probably occurs there. Our specimens are from near Boulder (6,000 ft), Station 2a, Sunshine Canyon at 7,600 ft, lake shores at 8,000 to 9,000 ft, west of Nederland at 9,600 ft, and Station 4a (10,000 ft). (Adults as early as April 2 at 6,000 ft, April 30 at 7,600, ft, and as late as the end of September at 8,800 ft; only one juvenile, May 26, at 7,600 ft.)

Tetrix ornata ornata and T. subulata occur together along the little stream in Chicken Ranch Gulch (Station 2a), presenting, perhaps, a prob- lem in competition.

ACRIDIDAE: RoMALEINAE

The subfamily Romaleinae has only one species, Brachystola magna (Girard), the lubber grasshopper, as far north as our region. It ranges on the plains from Mexico to Montana and North Dakota, being more common in the south. It is a mixed feeder and in the south may cause some economic losses (Isely, 1944). In our area, though not restricted to one plant, it appears to be definitely associated with the sunflower, Helianthus pumilus.

Our collections have all been from below 6,000 ft, the highest locality being Station ic-which is also the highest station for several other species of the plains fauna. B. magna is moderately common, hatching by the first week of June at Station la and about two weeks later at the slightly higher station, ic. First adults appear at 5,400 ft the second week of July, and at 5,750 ft just before the end of July. Thus development is about two weeks later at Chautauqua Mesa than in the pasture south of Boulder. This seemingly excessive delay at the slightly higher station may reflect the mar- ginal nature of this upper altitudinal limit. Adults persist at both stations into October.

Specimens of Brachystola magna collected in our area, 1958-1960: 125 juveniles, 77 adults.

ACRIDIDAE: CYRTACANTHACRIDINAE

The subfamily Cyrtacanthacridinae (Uvarov, 1966a) includes only one species, Schistocerca lineata Scudder, in our area. Though it is a strong flier we have collected no adults above altitudes at which we have taken juveniles.

Hubbell (1960) summarized the ecology, geo- graphical distribution, and taxonomy of this species, citing some of our specimens. He and Gang- were (1961) pointed out that it is often associated with trees and shrubs, and that it feeds on leaves of broad-leafed woody plants as well as forbs. We have collected it at several places at the lower edge of the mountains and up to 6,700 ft in areas of scattered ponderosa pine.

S. lineata appears late in the season. The only juveniles taken in 1958-1960 were eight late instars during the last half of August, but we have records of juveniles at 6,600 ft as early as July 24 in 1949, and adults at the same place Aug. 5, 1949. Eleven adults were collected in ponderosa pine at 6,200 ft, near Boulder, Aug. 17, 1948. Adults persist through September and into Oc- tober.

ACRIDIDAE: CATANTOPINAE

The subfamily Catantopinae (Uvarov, 1966a; Melanoplinae of others) includes all genera

formerly combined with Schistocerca, in most American treatments of Acrididae, under the Cyrtacanthacridinae. It includes 25 species in our area, 18 of these in the genus Melanoplus. We summarize their altitudinal distribution in Table 3, and we treat individual species under altitudinal categories.

Our most abundant and most widely distributed species are in this subfamily. The major pest grasshoppers of the region are three members of the genus Melanoplus (M. bivittatus, M. packardii, M. sanguinipes). Though not all members of this subfamily are versatile feeders these three eat both forbs and grasses, and they occur in a variety of habitats. They have wide latitudinal ranges, too, so it is not surprising that they also have wide altitudinal ranges. One species of Melano- plus, M. spretus (Walsh), the "Rocky Mountain Locust," was abundant in this region a century ago but has not been found during the past 60 years and is presumably extinct.

In contrast to the pest species are several members of the subfamily that feed only on particular kinds of plants or closely related groups of plants. These may be quite restricted, both in habitat and in altitudinal range. The contrasts among species Within this subfamily demonstrate practically all



400 GORDON ALEXANDER AND JOHN R. HILLIARD, JR. ool. 3M9o No. 4

TABLE 3. Altitudinal distribution of the Catantopinae of the Boulder region. Altitudinal bands are in 103 ft. R, resident; A, accidental.

5-6 6-7 7-8 8-9 9-10 10-11 11-12 >12

Aeoloplides turnbulli* R A A Dactylotum pictum R Hesperotettix

speciosus R H. viridis* R R R A A A A Hypochlora alba R Melanoplus alpinus R R M. angustipennis R A A A M. bivittatus R R R R R A A A

M. borealis R M. confusvs R R R R A A M. dawsoni R R R R R A

M. differentialis R A A M. dodgei R R R R R R R M. fasciatus R R R R R M. femurrubrum R R A A A A M. gladstoni R? A M. infantilis A R R R R M. keeleri luridus R R A M. lakinus R M. marshalli R R M. occidentalis R A A A A A A A M. packardii R R R R R? A A

M. sanguinipes R R R R R R R? A Paropomala

wyomingensis R Phoetaliotes

nebrascensis R R

*See text for account of subspecies differences.

aspects of ecology in relation to altitude that are illustrated by Orthoptera in general.

On Plains Only. Ten species are apparently limited, as residents, to the plains in our area (i.e., below 6,000 ft).

Aeoloplides turnbulli (Thomas) has two subspecies in the Boulder region. These overlap in distribution (Wallace, 1955) along the eastern edge of the Colorado Rockies. We found both at Valmont Butte. The species feeds on Cheno- podiaceae, and Station lb is our only regular station where suitable food plants (e.g., Russian thistle) are common.

Most of our specimens are of A. t. bruneri (Caudell) but some appear to be typical A. t. turnbulli, and our records indicate a seasonal separa- tion. Adults of A. t. bruneri appear at Valmont Butte as early as June 10 and occur no later than the last week of August. The earliest A. t. turnbulli were collected July 30, the latest in October. Adults of both are present in August. (Juveniles, subspecies undetermined, were collected from June 10 to July 8.) It is odd that t. bruneri appears earlier in the season than t. turnbulli, because it has the more southern distribution; however, t. turnbulli is the smaller subspecies, which is what one expects in the form with the more northern range. We have records of two accidentals, both of A. t. bruneri: adult male, 7,700

ft, Aug. 7, 1933; adult female, Station 5a (12,100 ft), Aug. 4, 1960.

Specimens of Aeoloplides turnbulli collected in our area, 1958-1960: 61 juveniles, 84 adults.

Dactylotur picture (Thomas), the flightless "barber-pole grasshopper," is locally present late in the summer. A small colony at the northwest edge of Boulder provided the only specimens taken during 1958-1960 (one juvenile, 12 adults, Aug. 30, 1959). It is occasionally taken elsewhere near Boulder but our highest altitude record is 5,800 ft.

Hesperotettix speciosus (Scudder), which feeds on sunflowers (Helianthus) and other composites, is more limited in altitudinal distribution than are its host plants. We have collected it only on the plains, and no higher than 5,600 ft. Since it ranges only as far north as South Dakota in latitude this is not surprising. At Station la, hatching begins near the first of June and adults appear by the last week of July.

Hypochlora alba (Dodge), the sage grasshopper, has been found in our area only in association with the herbaceous sage, Arterisia ludouvicana. Cage tests indicate that it feeds almost exclusively on this plant, eating flowers as well as leaves, but it is not coexistent with the host plant, which occurs at altitudes considerably higher than the range of H. alba. We have not found this grasshopper higher than about 6,000 ft.

Most specimens in 1958-1960 came from the pasture south of Boulder and from Chautauqua Mesa. (At Station la, hatching from about June 1 to July 1; at Station ic, ten days to two weeks later. Adults appear at Station la about mid- July; at Station ic the last week in July; they are present through October.)

Specimens of Hypochlora alba collected in our area, 1958-1960: 552 juveniles, 495 adults.

Melanoplus angustipennis (Dodge) is so in- frequently taken in our area that we are unable to interpret its true status. A common species on the plains further east, it was represented in our 1958-1960 studies by only one collection, 13 males and 15 females, adults, from White Rocks (5,100 ft), five miles northeast of Boulder, Aug. 15, 1958. Perhaps habitats suitable for it (Cantrall, 1943) are scarce in our area. We have fewer than a dozen records, all adults, prior to 1958, ranging up to 8,500 ft, the higher ones undoubtedly accidentals.

Melanoplus differentialis (Thomas), while widely distributed throughout the country, was rare at our collecting sites, where most of those collected were adults. The species is more common in local gardens and grain fields than in areas of mixed native vegetation. Mrs. Caplan (1966)




found it quite common in fields in the northeast edge of Boulder in 1964, when she was testing it for food plants. She found that its spectrum of food plants varied somewhat from that of M. bivittatus, but the differences were not great. M. differentialis ate grasses to a greater extent than did the other species, but both utilized forbs more than grasses. Isely (1944) found that field- collected first and second instar juveniles of M. differentialis reached maturity about 12 days earlier when fed a variety of forbs than when fed a variety of grasses.

This species probably reaches peak abundance at Boulder late in the season, after the peak for M. bivittatus (Caplan, 1966). We collected juveniles from the last of June to mid-August, adults from mid-July into October. Two accidentals, both males, were taken: near Nederland (8,500 ft), Aug. 8, 1931; at timber line, Mt. Evans (11,500 ft), Sept. 19, 1959.

Melanoplus gladstoni Scudder is represented by only a few specimens from our area. It is a late season form, confined to the plains and much commoner east of our area. We collected an adult male at Station la, Aug. 14, 1958, and another at 6,600 ft, Oct. 7, 1949, both probably accidentals, as all our other records are from at least a few miles further east.

Melanoplus lakinus (Scudder), a short-winged, flightless grasshopper, was regularly collected at Valmont Butte, rather commonly at White Rocks (5 miles northeast of Boulder), and occasionally at Station la. All our specimens are from below 5,600 ft, and the species is much more common on the plains away from the mountains than near them. M. lakinus is a mixed feeder but its selection of food plants is different from that of either M. bivittatus or M. differentialis (Caplan, 1966). Hatching occurs about the first of June; adults appear in mid-July, are present into October or later but pass their peak of abundance by the end of August.

Melanoplus occidentalis (Thomas), an early season form of uncertain status, is resident but rare as high as Station la. We collected nearly 50 adults in 1958-1960, about a third of these above 7,000 ft. The species is a strong flier and a wanderer (LaRivers, 1948), so we consider all our specimens from the mountains accidentals.

Paroponala wyomingensis (Thomas) is associated with lush, moderately thick-stemmed grasses like Andropogon. It habitually perches vertically, along and in contact with the grass stem, so, with its slender, elongated form it is inconspicuous. It is, however, easily taken in sweep nets. We have found it no higher than 5,300 ft, most of our

specimens from White Rocks, a few from Valmont Butte. It hatches about June 1; adults appear by the second week of July and are most common in mid-August.

On Plains and in Mountains. Nine species of Catantopinae occur both on the plains and in the mountains. Eight of these are common on the plains, but one, Melanoplus dawsoni, is a montane form that ranges downward only to the upper edge of the plains.

Hesperotettix viridis (Thomas), which feeds on composites (especially Grindelia), is represented in our area by two subspecies. H. v. viridis and H. v. pratensis Scudder. According to Hebard (1931) these occur together in western Kansas but do not appear to intergrade. We have had no difficulty in assigning most adults to one or the other subspecies, and our collections suggest that H. v. viridis is limited to the plains while H. v. pratensis occurs from the upper edge of the plains to over 7,000 ft. Neither is limited in this distribution by absence of suitable food plants. This altitudinal distribution is correlated with latitudinal distribution, H. v. viridis being the more southern form (Arizona to Texas, north to South Dakota), while H. v. pratensis overlaps v. viridis in the northern part of the latter's range but extends northward into Montana and Alberta.

Chautauqua Mesa was the upper limit for H. v. viridis except for two accidentals (7,700 ft and 8,500 ft). It was the lower limit for H. v. pratensis, whose upper resident limit appeared to be about 7,600 ft (in Sunshine Canyon). These ranges are based on adults; we did not attempt to assign juveniles to subspecies, though we assumed that those at Station la were all v. viridis and those from 2a were v. pratensis because all adults at these stations were of the corresponding subspecies. Hatching of v. viridis at Station la was late in May and adults appeared early in July. Juveniles of H. v. pratensis appeared at Station 2a, 1,300 ft higher, by June 7; adults by mid- July. (The dates at Chautauqua Mesa and the south pasture were about the same, with adults of t. viridis appearing on the average a little earlier than those of t. pratensis at ic.) At all stations the hatching period was long, juveniles were present about two months, and adults were collected into September.

Specimens of Hesperotettix viridis collected in our area, 1958-1960: 426 juveniles, 474 adults.

Melanoplus bivittatus (Say) is one of the most abundant and most destructive species in our area. It feeds on a wide variety of plants, and we have found it at all collecting sites within its altitudinal range. It is a close ecological equivalent of the




locally scarcer M. differentialis, but there are slight differences in foods (Caplan, 1966). Both M. bivittatus and M. differentialis have wide geographic ranges, but, in our area, bivittatus is established as a resident regularly up to 8,500 ft while differentialis does not range into the mountains. This difference correlates with their ranges elsewhere. Both species occur in Arizona, where bivittatus is in the higher elevations of the northern part and differentialis is present primarily in the south (Ball et al., 1942). Only bivittatus occurs as far north as Manitoba and Alberta (Brooks, 1958), while only differentialis extends into Mex- ico to the south.

M. bivittatus may range as a resident up to 10,000 ft in a favorable year, but in most years a hard frost occurs early enough at that altitude to eliminate the species. It completed its life cycle up to 8,500 ft in all three years of our intensive collecting, and we believe it may occasionally do so up to 10,000 ft. It appears frequently at high altitudes as an accidental, some 80 having been collected at 10,000 ft and above during 1958- 1960 (G. Alexander, 1964). The occurrence of so many accidentals is surprising for a species that, as Cantrall (1943) remarked, appears "slug- gish," but both sexes often fly rather vigorously when disturbed, and they must reach the higher altitudes by a series of short flights.

Hatching below 6,000 ft is from mid-May through June; adults appear before the end of June and are present into October. At 7,000 ft hatching is from near the end of May through the first week of July, and the first resident adults appear about mid-July. At 8,500 ft, limited collections suggest hatching before the end of June, extending through mid-July; the first adults that complete their life cycle at this altitude appear about the second week of August. (Acci- dentals from lower elevations appear approximately a month before adults mature at this altitude.) Our few juveniles from 10,000 ft suggest that hatching occurs through the first three weeks of August. The first adults that might mature at this altitude could hardly appear before mid- September; in most years "winter" has already arrived at 10,000 ft by then.

Specimens of Melanoplus bivittatus collected in our area, 1958-1960: 5,042 juveniles, 1,518 adults.

Melanoplus confusus Scudder is the first grasshopper to hatch in our area. Its hatching period is short; adults mature, deposit eggs, and are gone, even at the highest elevations where they are resident, by the end of August. There is some overlap between this species and the more abun-

dant M. sanguinipes, and the females of these two species are readily confused, but the males are easily distinguished.

This species is a mixed feeder, eating forbs predominantly. It occurred at all regular collecting stations up to 8,500 ft, and as accidentals up to 10,000 ft. A strong flier, it appears as an accidental at montane elevations within its resident range before adults have matured at such elevations. Hatching below 5,500 ft is from mid-April through May; at Chautauqua Mesa it is about three weeks later; at 6,700 ft, from mid-May to mid-June; and at 8,500 ft, in early June. Adults appear at lowest elevations about the end of May; at 5,750 ft in mid-June; at 6,700 ft soon after; and at 8,500 ft by early July. At lower elevations adults persist only through July, but at higher elevations they persist into August.

Specimens of Melanoplus confusus collected in our area, 1958-1960: over 600 juveniles, 1,353 adults.

Melanoplus dawsoni (Scudder) is a small, short-winged species, predominantly montane, extending down to the plains only at our highest plains station, ic. It is resident from 5,750 to 10,000 ft but common only up to 8,500 ft. It reaches its western limit in the Rocky Mountains, where it occurs south into New Mexico; in the northern states it extends eastward into New England.

In all populations we studied hatching takes place over a long period of time, juveniles being present for many weeks. At Chautauqua Mesa, where hatching occurs from the last of May to the second week of July, and adults appear by the first of July, it is not uncommon to collect all stages in a single collection. Adults are common by mid-July and persist into October. At Station 2a, about a thousand feet higher, hatching occurs from about June 1 to mid-July, and first adults appear during the second week of July and persist into the fall. At 8,500 ft all stages are about two weeks later than at 6,700 ft. The species is resident at 10,000 ft but rare; there the first adults appear during the second week of August.

Our information on age distribution in populations of M. dawsoni is so extensive that we have summarized it in Fig. 16-for the three stations from which the largest numbers were taken in 1960. Collecting dates at intervals of approximately two weeks were selected to reveal the seasonal progress of the shift in age groups at different altitudes.

Specimens of Melanoplus dawsoni collected in our area, 1958-1960: 1,004 juveniles, 952 adults. Note: Of the 952 adults only three, two females




8,500

/ /

/

6,700 - -

5,750'1 _

June July August Sept. FIG. 16. Stages in the life cycle of Melanoplus daw-

soni in relation to altitude. Stippled: Instars I & II. Horizontal lines: Instars III & IV. Vertical lines: Instar V. Black: Adults. Based on data from Stations 1c, 2a, and 3b in 1960. Total specimens: 361 juveniles, 140 adults. The broken line indicates projected seasonal delay according to Hopkins (1919). (See DISCUS- SION.)

and a male, were macropterous, one of the females an accidental at 12,200 ft (G. Alexander, 1964). All others were brachypterous.

Melanoplus femurrubrum (DeGeer) is widely distributed throughout the United States and Can- ada but in our area is common only in the more moist habitats. Its preference for lush vegetation has been pointed out by Brooks (1958) and Helfer (1963). Our most extensive collections were along a drainage ditch at Station lb and along a tiny stream in Chicken Ranch Gulch. The species is a mixed feeder, with preference for dicot leaves (Gangwere, 1961).

Hatching occurs over a long period, but the species is not very common until late in the season, and it is particularly late above 6,000 ft. Hatching at Station lb begins in late May and continues through June and July. The first adults appear by the end of June, but adults are not common before the end of July. At Station 2a some may hatch in early June, but juveniles are present over a long period and late juvenile instars are found to the end of August. Though the species should mature by the middle of July at 6,700 ft our earliest record of an adult is August 6. Adults regularly mature up to that altitude but possibly not higher. A few accidentals have been collected, one even at 11,000 ft. Adults are quite cold- hardy; they persist late in the fall, as was noted by Cantrall (1943). We have collected several in or near Boulder in November, two as late as the first week of December.

Specimens of Melanoplus femurrubrum collected in our area, 1958-1960: 337 juveniles, 143 adults.

Melanoplus keeleri luridus (Dodge) is a late season grasshopper of moderate abundance in dry,

open areas, where it is resident up to 6,700 ft, possibly higher, but it appears too late in the season in our area to become established at high altitudes. It is a mixed feeder, forbs predominating in its diet (Gangwere, 1961).

Hatching below 6,000 ft is from mid-June through July, first adults appearing in July but not becoming common before the second week of August. Above 6,000 ft hatching is about a week later but few adults are seen before the last half of August. (We have taken two accidentals, both at approximately 7,600 ft.) Adults survive into October and even November.

Specimens of Melanoplus keeleri luridus collected in our area, 1958-1960: 281 juveniles, 104 adults.

Melanoplus packardii Scudder, an abundant Colorado grasshopper and one of our pest species, is regularly resident up to 8,500 ft in our area. It is a mixed feeder, preferring forbs (Brooks, 1958), and probably only M. sanguinipes and M. bivittatus do more damage to crops in eastern Colorado. One juvenile collected at 10,000 ft suggests the potential for a resident population at that altitude but we found no evidence that adults matured above 8,500 ft during the period of our study. Accidentals were taken up to altitudes in excess of 11,000 ft.

Hatching below 5,500 ft begins in late May and continues through June, July, and at least until the middle of August. (Juveniles have been taken at Valmont Butte during the last half of September and even during the first week of October, suggesting a second hatch late in the season, perhaps from eggs laid by adults that matured first during the same season. Such eggs would have hatched without diapause, presumably.) Adults are present below 5,500 ft from the last of June into October, occasionally November.

At Chautauqua Mesa and other places between 5,500 and 6,000 ft hatching extends over a period from soon after June 1 to the third week of July, and juveniles are present until late August. The earliest adults appear before the end of June and adults are present into October. At Stations 2a and 2b hatching is from mid-June or earlier to the third week of July, with the earliest resident adults appearing early in July; and, at Station 3a, the highest altitude at which the species appears to complete its life cycle, hatching occurs from the last of June into the second week of July, and resident adults appear in mid-July and persist into October.

Specimens of Melanoplus packardii collected in our area during 1958-1960: 2,675 juveniles, 1,113 adults.



404 GORDON ALEXANDER AND JOHNR. HILLIARD, JR. Ecological Monographs

Melanoplus sanguinipes (Fabr.), referred to as M. mexicanus (Saussure) or M. biliturcatus (Walker) in various earlier papers, is our most abundant species and most serious economic pest among the grasshoppers. (See Gurney, 1962, and Kevan & Vickery, 1965, for discussion of the nomenclature.) It feeds on both grasses and forbs (Pfadt, 1949b). We found it at all collecting stations on the plains and in the mountains, resident up to 8,500 ft regularly, up to 10,000 ft in a moderately favorable season, and apparently up to 12,000 ft where a late season and suitable exposure were particularly favorable. It has been taken as an accidental more frequently than any other species, and at all elevations up to 14.100 ft (G. Alexander, 1964).

Hatching of M. sanguinipes extends over a very long period-some three months on the plains- and adults are therefore present during a long season. Cantrall suggested (1943) that there might be two generations per year on the George Preserve, Michigan. We think this is possible in our area, too; eggs deposited by adults maturing early in the season may hatch and the young from these mature into a second generation of adults within the same season. We have experimental evidence that some females in our area lay eggs that hatch without diapause.

Below 5,500 ft eggs hatch from mid-May, possibly earlier, through July. Adults appear by mid- June, so we have frequently collected all five juvenile instars and adults at the same time. Adults are abundant from the first of July into September, and they may persist into November. Hatching is only a little later at Chautauqua Mesa.

At Stations 2a and 2b hatching occurs through June, July, and into August. The first resident adults appear about the fourth week of June; adults persist into late fall. At 8,500 ft hatching begins some two weeks later than at 7,000 ft, and the earliest resident adults appear in mid-July, but adults occur as late as October.

At Station 4a, the highest elevation at which adults matured in our area, juveniles were not common. Hatching began, apparently, about the end of June and continued past the end of August (at least in 1959, a favorable year). What we presumed to be resident adults were collected as early as August 29, 1959. In 1960, however, our last collection of juveniles was August 18, two nights after a hard freeze that had killed much of the herbaceous vegetation. (The Thermopsis was blackened, for example.) Later collections that season suggested that the species did not complete its life cycle at 10,000 ft. These observations sug-

gest that the date of the first severe freeze in the fall determines the upper resident limit.

In 1959, juveniles in the first to fifth instar, inclusive, were collected on a south-facing slope of alpine tundra at 12,000 ft, just west of the old mining camp of Waldorf, on August 20. (This locality is a little west and north of Mt. Evans.) Adults were collected at the same place and up to more than 13,000 ft the same day. It thus appears likely that in a favorable exposure, and during a late season, this species may mature up to 12,000 ft. This wide altitudinal range is not surprising since M. sanguinipes occurs quite far north, even north of 650N. in both Canada and Alaska (Vickery, 1967). Furthermore, Parker's laboratory observations (1930) on this species and Camnula pellucida demonstrated that M. sanguinipes is active at a lower temperature than is Camnula. (In our area, Cannula is not common above 10,000 ft.)

Specimens of Melanoplus sanguinipes collected in our area, 1958-1960: 4,164 juveniles, 3,284 adults.

Phoetaliotes nebrascensis (Thomas), the big- headed grasshopper, a (usually) short-winged species, regularly matures up to 6,000 ft in our area, but we have one pair of adults, both brachypterous, collected at 8,500 ft, and several specimens from about 7,000 ft. Its limited altitudinal distribution may be due to lack of suitable habitats above the plains, for it is predominantly a grass-feeder (Cantrall, 1943; Gangwere, 1961; Pruess, 1969). Its latitudinal distribution suggests that it should occur up to 8,500 ft or more, for it ranges from Mexico into Alberta and Saskatchewan (Brooks, 1958).

Hatching at Station la is from early June into the second week of July; adults appear before the end of July and persist into late fall. Hatching at Chautauqua Mesa is about a week later and at 6,000 ft on Flagstaff Mountain still later. This species is a moderately common late season form that barely invades the mountains.

Specimens of Phoetaliotes nebrascensis collected in our area, 1958-1960: 412 juveniles, 221 adults.

In Mountains Only. Six species, all in the genus Melanoplus, are limited to altitudes within the mountains. All are primarily boreal in distribution, reaching their southern limits only at high elevations in the southern Rocky Mountains. Two of the six are represented in our area only by small, relict populations.

Melanoplus alpinus Scudder reaches its southern limit in our restricted area. It is a grass-feeder (Brooks, 1958), but it is not wide spread. In western Boulder County, in the Rainbow Lakes




region, a relict but well established population occurs in small clearings in the subalpine zone at about 10,000 ft and somewhat lower, and up to 10,800 ft in the tundra just above timber line. This population was the basis for an earlier reference by the senior author (1951) but Hebard had previously (1929) given its southern limit as some 50 miles further north. We made large collections on two occasions: 105 adults and 148 juveniles, Aug. 11, 1949, at 10,800 ft; 86 adults, 30 juveniles, Aug. 7, 1960, at 10,000 ft. The juveniles were all in the last two juveniles instars, most of them in the last. These and other observations suggest that all eggs hatch at near the same time in early to mid-July and that development of the population is approximately syn- chronized.

Melanoplus borealis borealis Fieber, as M. alpinus, is represented within our area by a relict population. Though the species ranges in the north into northern Canada and Alaska (Vickery, 1967) and in Colorado as far south as Pikes Peak and the Sangre de Cristo Range (G. Alexander, 1951, as M. b. monticola), we have found it in only one Colorado locality north of Pikes Peak. This is a moist shrub area immediately below timber line on the east side of the Continental Divide near Jenny and Yankee Doodle Lakes (southwest Boulder County and northwest Gilpin County, along the Rollins Pass Road). We have found it only between 10,500 and 11,200 ft. Though said to be a mixed feeder (Brooks, 1958) or a grass feeder (Hebard, 1936c), we believe it feeds primarily on broad-leafed plants in lush, moist vegetation. Hatching occurs through July. The earliest adults appear by the end of that month, and adults are present into September.

Specimens of Melanoplus borealis borealis collected in our area, 1958-1960: 85 juveniles, 71 adults.

Melanoplus dodgei (Thomas), a flightless, short-winged grasshopper, is the most abundant and most widely distributed Melanoplus restricted to our mountains. It has well established populations from 6,700 to over 12,000 ft in our area, and we have taken one specimen at about 6,000 ft and several above 13,000 ft. In latitude it ranges from the mountains of northern New Mexico into southern Montana, but it is confined to the southern and middle Rocky Mountains. Several sub- specific names have been used in the M. dodgei complex (see Van Horn, 1965), but we are treat- ing all our populations only under the specific name.

M. dodgei is more likely to be present in stands of mixed herbaceous vegetation than in predomi-

nantly grassy areas, but crop analysis shows that it is definitely a mixed feeder. Forbs fragments usually predominate, but crops are occasionally filled with grass fragments only. The versatility of this species in use of food plants may explain why it is present in even small clearings throughout the montane forest, for it is not limited to extensive open areas as is Aeropedellus clavatus, our other widely distributed montane grasshopper.

Hatching at 6,700 ft occurs from early May into the first week of June; at 8,500 ft, from mid-May to mid-June; at 10,000 ft, during the first to third weeks of June; and at 12,100 ft (Station 5a), from mid-June into the second week of July. Adults appear at 6,700 ft before the end of May; at 8,500 ft, soon after mid-June; at 10,000 ft, about July 1; and at 12,100 ft, the third week in July. Adults persist at high altitudes into Sep- tember and at all lower altitude stations into October.

Our collections of M. dodgei have been so extensive that we have rather definite information on hatching dates and the appearance of juveniles of different ages, as well as adults, at several stations between 6,700 and 12,100 ft in altitude. We have summarized this information in Fig. 17, a graph of age distribution in the different populations at time intervals during the 1959 season.

Specimens of Melanoplus dodgei collected in our area, 1958-1960: 1,382 juveniles, 3,289 adults.

Melanoplus fasciatus (F. Walker) is a short-

12,100'

/ /

/

10,000' il /

/

/

/

6 , 9000L May June July August Sept.

FIG. 17. Stages in the life cycle of Melanoplus dodgei in relation to altitude. Stippled: Instars I & II. Hori- zontal lines: Instars III & IV. Vertical lines: Instar V. Black: Adults. Data from Stations 2a & 2b (pooled, mean elevation 6,800 ft), 3b, 4a, and 5a, in 1959. Total specimens: 768 juveniles, 1665 adults. The broken line indicates projected seasonal delay according to Hopkins (1919). (See DISCUSSION.)



406 GORDON ALEXANDER AND JOHN R. HILLIARD, JR. Ecological Monographs 406 GORDON ~~~~~~~~iVol. 39, No. 4

winged, moderately common grasshopper in clearings in montane and subalpine forests of our area from the foothills (6,700 ft) to timber line, at about 11,000 ft. It is widely distributed across southern Canada and the northern States, and south in mountains as far as Tennessee, Arkansas, and New Mexico. It feeds primarily on broad- leaf plants. In some sections of the country it is called the "huckleberry grasshopper," but it is not limited in Colorado to localities where our small Vaccinium occurs. Hatching dates at 6,700 ft are through June into early July; at 8,500 ft, from the second week of June to the second week of July; and at 10,000 ft, only slightly later, from mid-June to mid-July. Adults appear at 6,700 ft by mid-June; at 8,500 ft, a week later; and, at 10,000 ft, almost as soon as at 8,500 ft. Adults persist into September.

Specimens of Melanoplus fasciatus collected in our area, 1958-1960: 357 juveniles, 309 adults.

Melano plus infantilis Scudder, the smallest species of Melanoplus in our area, is a grass feeder that, in our experience, is more definitely limited to grassy areas than is any other species of Melan- oplus. Though not abundant, we have found it regularly present, rather late in the season, between 8,000 and 10,000 ft in altitude. Several specimens have been taken as low as 6,700 ft, where it is probably resident, and we have taken one specimen each at Stations la and ic, where it is probably accidental. Hatching at 8,500 ft apparently begins before the end of June and continues through July; adults appear during the last half of July and are present into September. Hatching at 10,000 ft is a week or two later, and adults are present by the second week of August.

Melanoplus marshalli marshalli (Thomas), or- iginally cited from Colorado as M. oregonensis marshalli by Hebard (1928, 1929), was separated from M. oregonensis in Hebard's (1936b) revision. In this later paper, Hebard stated that the species occurred "from 10,000 ft or over in the Hudsonian Zone," and that it had not been found "anywhere much west of the continental divide." We have found it only between 10,000 and 11,700 ft in our area, but it is not limted to the subalpine forest. It occurs frequently in alpine tundra. And Hebard's statement that it is not found much west of the Continental Divide is incorrect, for it occurs at more localities west of the divide in Colorado than east of it.

In our area we have found this species from timber line west of Rollins Pass to the Pass, in Fourth of July Valley (west of Nederland), and, a few miles to the north, in Hidden Valley (Rocky

Mountain National Park). The juveniles we collected, mostly in late stages, suggest that hatching occurs through the last three weeks of June and through July; adults appear before the end of July and persist well into September.

Specimens of Melanoplus marshalli marshalli collected in our area, 1958-1960: 123 juveniles, 271 adults.

ACRIDIDAE: OEDIPODINAE

This subfamily is distributed in all parts of the world but predominantly in drier (and warmer) climates. It is well represented in the western United States. Most species have brightly colored hind wings, and many produce a crepitating sound in flight by the rapid opening and closing of the hind wings (Isely, 1936).

Some of the most serious insect pests in the Old World, the migratory locusts, are members of this subfamily. One of our local accidentals, Dissosteira longipennis, has been a serious economic pest southeast of our area, and it has even developed migratory swarms (Wakeland, 1958). A widely distributed montane form in the Boulder region, Camnula pellucida, is a serious crop pest further north (Riegert et al., 1965), where it occurs at lower altitudes. But no species of the Oedipodinae has been a serious economic pest in our area.

The 27 species of Oedipodinae we have found in the Boulder region are treated individually under distributional categories. Table 4 summarizes their altitudinal distributions.

On Plains Only. No one of the 11 species of Oedipodinae whose records are limited to the plains in the Boulder region is abundant, though two are moderately common. Several are known only from scattered records, one has been collected only once since 1947, and one is known only from sight records.

Aerochoreutes carlinianus carlinianus (Thomas) is a rather large, mid-summer form. According to Brooks (1958) it is a grass feeder, favoring Agropyron smithii, but is more restricted in our area than is Agropyron. All local records are from limited areas on the plains, almost all from White Rocks and Gunbarrel Hill, both a few miles northeast of Station lb.

Derotmema, haydenii (Thomas), a small species, widely distributed in the west, is most common in dry, grassy areas. We have found it fairly common only at Valmont Butte, where hatching is probably before mid-June. Adults appear there by mid-July and are present through August.

Dissosteira longipennis (Thomas), the High Plains Grasshopper, has not been collected in our




TABLE 4. Altitudinal distribution of the Oedipodinae of the Boulder region. Altitudinal bands are in 103 ft. R, resident; A, accidental.

See text for account of Xanthippus corallipes subspecies.

5-6 6-7 7-8 8-9 9-10 10-11 11-12 >12

Aerochoreutes carlinianus R

Arphia conspersa R R R R R R A. pseudonietana R R A A A Camnula pellucida A R R R R R Chortophaga

viridifasciata R R R Circotettix rabhla R R R R R A Cratypedes neglectus R R R Derotmema hayldenii R A A Dissosteira carolina R R A A A D. longipennis A Encoptolophus

sordidus costalis R Hadrotettix

trifasciatus R A A A Hippiscms rugosus R Mestobregma plattei R A Metator pardalinus R A A A A A A Pardalophora

haldemanii R Spharagemon collare R R A A A A A S. equale R R R A Trachyrhachis kiowa R R R A A A A Trimerotropis

campestrs R R R R T. cincta R R R R T. humile A R R R T. laticincta R T. pallidipennis R R R A A T. suffusa A R R R R R A Tropidolophus

formosus R Xanthippus

corallipes R R R R R R R

area, but the senior author saw two in Boulder in August, 1938, but was unable to capture either. This was during a major outbreak of the species, with large migratory populations less than 100 miles southeast of Boulder (Wakeland, 1958). This serious economic pest may have invaded our area in the past but there is not evidence that it ever became established as a resident.

Encoptolophis sordidus costalis (Scudder) appears quite late in the season, and we have not collected it above the upper edge of the plains grassland. Most of our collections have been just below the lower edge of coniferous forest. It is a grass feeder (Brooks, 1958; Gangwere, 1961), and suitable habitats may be scarce at higher altitudes. Our small collections indicate that it may hatch in July; but adults are not numerous before late August or September-another reason for its apparent upper altitudinal limit.

Hadrotettix trifasciatus (Say) is a large, brightly colored, mid-summer species that occurs throughout the high plains in grassy areas that are usually on gravelly soil. All our collections were at Stations la and lb. Hatching is near the end

of May or first of June; adults appear by the second week of July and are present through August and into September.

Specimens of Hadrotettix trifasciatus collected in our area, 1958-1960: 72 juveniles, 114 adults.

Hippiscus rugosus (Scudder), a widely-distributed, robust species, is rare in our area. We collected only three, all adults, during 1958-1960 (Aug. 7 to 27), all at Station la.

Mestobregma plattei (Thomas) has been taken in some numbers at our plains stations. Accord- ing to Helfer (1963) it occurs on rocky soil with sparse grass; our selected sites have been perhaps more mesic than its preferred habitat, though we found populations of moderate size. All our recent collections are from Stations la and lb, where hatching occurs about the second week in June, and the first adults appear before mid-July. Adults are most common during Au- gust. Though the species is long winged, we have few records of accidentals, the highest being from 7,500 ft.

Specimens of Mestobregmc plattei collected in our area, 1958-1960: 33 juveniles, 122 adults.

Metator pardalinus (Saussure), a moderately large, long-winged oedipode, has frequently been collected as an accidental, even above timber line (G. Alexander, 1964), but it has been taken as a juvenile only on the plains. It is a grass and sedge feeder (Brooks, 1958). It hatches at Station la soon after June 1; adults appear during the first week of July and persist into September.

Pardalophora haldemanii (Scudder) matures so early in the season that it undoubtedly overwinters as a late juvenile. It is rare in our area. Our few records, for adults only, range from June 20 to July 29.

Trimerotropis laticincta Saussure, while a common species on the plains further east, is rare in our restricted area. We have taken a few adults late in the season on somewhat alkaline flats about 6 miles northeast of Boulder.

Tropidcolophus formosis (Say) reaches its northern limit not far northeast of our area, and this brilliantly colored grasshopper is now rare near Boulder. A small population existed in the 1930's on the south side of Valmont Butte, but the species has not been found there since the chemical plant was built in 1937. (The railway spur and road to the plant were constructed across the area occupied by the small population.) Sev- eral juveniles were collected in the pasture north of Boulder in July and August, 1947, but that area is now being developed commercially. The only specimen taken recently was collected Sept.



408 GORDON ALEXANDER AND JOHN R. HILLIARD, JR. Voil. 39, No. 4

30, 1965, 7 miles north of Station lb. The species may still be represented by one or more small populations on the plains near Boulder. It always appears late in the season, juveniles from late July into August and adults from August into September.

On Plains and in Mountains. Nine species of Oedipodinae occur on the plains and up to various elevations in the mountains. Only two of these have wide altitudinal ranges; the others are predominantly plains forms that invade only the lower elevations. Several species are quite common, and several species that are relatively uncommon in our area are much more common on the plains a little further east.

Arphia conspersa Scudder, the earliest species to become adult in the spring, is a brownish grasshopper of moderate size, with yellow to (rarely in our area) reddish wings. (See Willey & Willey, 1967, for a discussion of wing color distribution in Colorado populations.) It matures very early, occasionally even in late winter, often having entered the winter as a fifth (last) instar juvenile; it may have a two-year life cycle, the first year in the egg (Pickford, 1953). Juveniles can withstand freezing (G. Alexander, 1967). The species is less dependent on lengthening photoperiod for stimulation of molting than either Chortophaga or Xanthippus (Halliburton & Alexander, 1964). It is a mixed feeder, preferring grasses and sedges (Brooks, 1958); we have observed that all species overwintering as juveniles feed on grasses. Since its geographic range is from Mexico to northern Canada and Alaska (Vickery, 1967) one is not surprised that it is resident to above 10,000 ft in altitude.

Adults appear commonly in April below 6,000 ft, but we have records of adults maturing during the winter (following periods of mild weather). Adults appear at Stations 2a and 2b in April, at 3a in May, and at 4a by the second week of June. They may occur as late as July-even later at highest elevations. We have taken no adults above the resident range.

Juveniles hatch at about the same time at all elevations, late July and early August. Some have reached the third instar in September at all altitudes, and they are usually in the third or fourth instar in October. By November most are in the fifth instar, in which they overwinter, and our latest records of fifth instar juveniles in the spring are in late April below 6,000 ft, mid-May at about 7,000 ft, the first half of June at 8,500 and 10,000 ft.

Arphlo conspersa

Juveniles Adults Eggs Juveniles

Arphia pseudonletana

Eggs /Juv's dults Eggs

J F M A M J J A S O N D Months

FIG. 18. Comparison of events in the life cycles of Arphtia conspersa and A. pseudonietana during the year. Times may be considered those for approximately 6,000 ft above sea level for both species. It is possible that A. conspersa is in the egg stage through the first winter, hatching only in the second season (Pickford, 1953), though juveniles and adults appear as indicated in the graph.

Specimens of Arphia conspersa collected in our area, 1958-1960: 169 juveniles, 566 adults.

Arphia pseudonietana (Thomas) and A. conspersa illustrate nicely a pattern of reproductive isolation that makes possible the sympatric occurrence of such closely related species. These two are reproductively isolated by a difference in time of life cycle (Fig. 18). A. pseudonietana matures after midsummer, at about the time the eggs of A. conspersa are hatching. Its eggs are laid late in the summer, and the species overwinters in the egg stage. A. pseidonietana is a late season form and is primarily a grass feeder. It is resident in our area on the plains and up to lower montane elevations, this altitudinal range correlating well with its geographic range from Arizona and New Mexico, into southern Canada.

Hatching at Station la begins near mid-June and about a week later at Chautauqua Mesa. The earliest adults are usually collected during the first week of August below 6,000 ft and in mid- August at the higher elevations of its upper resident limit (about 7,000 ft). A few accidentals have been collected, even up to 10,000 ft.

Specimens of Arphia pseudonietana collected in our area, 1958-1960: 65 juveniles, 163 adults.

Chortophaga viridifasciata (DeGeer) is a large, widely distributed species, that is relatively scarce in the Boulder region except locally in lush, grassy areas. Juveniles overwinter in the fifth instar, and the first adults appear early in April. Adults have not been collected after June. Hatch- ing occurs in August and September, and we have October collections of juveniles, below 6,000 ft, of the second to fifth instars, inclusive. Our highest collections including juveniles, and therefore residents, were from Chicken Ranch Gulch (6,700 ft) and from Sunshine Canyon at 7,600 ft.

Dissosteira Carolina (Linn.), the familiar Road Duster, is relatively uncommon in our area.




Though a strong flier, wary, and not easily caught, it is conspicuous in the field and not easily overlooked. Hatching on the high plains apparently occurs from the last of May through June; at 6,700, apparently its highest resident locality, hatching extends well into July. Earliest adults on the plains near Boulder were during the last week of June, but most adults seen are from mid- July into September. We have taken accidentals above 10,000 ft on a few occasions, but not above timber line. Fehlmann (1950), however, collected five in alpine tundra in the Sangre de Cristo Range.

Spharagemon collars (Scudder) is not common in our area, but we have records over many years, suggesting that the species is resident up to at least 6,700 ft. It hatches at plains stations late in May or early in June, and at 6,700 ft some two weeks later. Adults appear early in July on the plains, but resident adults probably do not mature at Station 2a until the end of July; they persist at all altitudes into September. Accidentals have been collected several times-up to 12,200 ft.

Spharagemon equale (Say), less common in our area than S. collare, is resident up to 7,200 ft. The small number of specimens collected indicate only that it matures before the end of July. We have records of two accidentals at 8,500 ft.

Trachyrhachis kiowa (Thomas), a small, long- winged oedipode with translucent wings, is a common species in our area. It has a wide geographic distribution, from Mexico to Canada, in grassland. Its upper resident limit shifts from year to year. The life cycle was completed in some seasons up to 7,000 ft or more, but in others (e.g., 1960) only adults were taken at our plains stations-these apparently being accidentals that had flown in from further east (G. Alexander, 1964).

If hatching takes place, it occurs at Station la about mid-June; at Stations 2a and 2b about three weeks later. (Juveniles were present at these higher stations in 1958 and 1959.) Adults appear on the plains during the first week in July and they are present into September. Numerous accidentals at 7,000 ft make it difficult to determine the time of appearance of resident adults but we believe it is about three weeks later than at 5,500 ft.

Specimens of Trachyrhachis kiowa collected in our area, 1958-1960: 44 juveniles (none in 1960), 166 adults (only 31 in 1960).

Trimerotropis pallidipennis (Burmeister) has a most extensive geographic range-from Canada into southern South America-but it is not common in our area, though it is apparently resident

up to about 7,000 ft. (We have taken one juvenile, fifth instar, at 7,200 ft, July 28.) Adults were collected from the third week of June to mid- August-as high as 8,500 and 9,000 ft; some of these were undoubtedly accidentals.

Xanthipptts corallipes Haldeman is a robust species occurring in grassland from Texas into northern Canada. In our area it is represented by a series of progressively smaller subspecies from the plains to above timber line. We recognize three subspecies in the Boulder region: X. c. lati- fasciatus Scudder, below 6,000 ft but quite scarce at the upper edge of the plains; X. c. leprosus Saussure, represented by large populations in grassy clearings in ponderosa pine forest from 6,500 to about 9,000 ft; and X. c. altivolus Scud- der, which we have found at only two locations in our area, both above timber line-I 1,000 ft on "Baldy," the eastern prolongation of Arapahoe Mountain, and 11,300 ft on Kingston Peak, southwest of Rollinsville. All three subspecies may have a two-year life cycle, spending the first winter in the egg stage and the second as juveniles (Pickford, 1953; Hewitt & Barr, 1967).

Adults appear by May 1 up to 7,000 ft, by the end of May at 8,500 ft, and before the end of June at 11,000 ft. Adults persist into mid-July on the plains and as late as mid-August, rarely later, at 6,700 ft or higher.

We have no data on juveniles of X. c. latifas- ciatus near Boulder, but adults as early as May 27, as well as collections from further east in Colorado-where this form is common-indicate overwintering juveniles. X. c. leprosus hatches at both 6,700 and 8,500 ft from the last of July through August, the higher altitudes apparently having no significant delaying effect. Most juveniles are in the third instar at the onset of winter, and these individuals can withstand freezing (G. Alexander, 1967). Studies during the winter of 1957-1958 by Douglas and Kathleen Alexander at about 7,000 ft, a few miles northwest of Boul- der, indicated that third instar juveniles pre- dominated until March. In early April, more fourth than third instars were found; and fifth instar juveniles appeared early that month and increased in relative numbers during that month. Our only records of early juveniles of X. c. altivolus are first and second instars in the "Baldy" population, Aug. 11, 1949; hatching is apparently during the second week of August and perhaps later. Juveniles of X. corallipes are a little later in molting at all altitudes than in Arphia conspersa, which overwinters mainly in the fifth




instar; hence, fifth instar juveniles of Xanthippus do not usually appear until spring.

Specimens of Xanthippus corallipes collected in our area, 1958-1960: 122 juveniles, 709 adults, mostly X. c. leprosus.

In Mountains Only. Of the seven species of Oedipodinae limited to elevations above the plains, one, Camnula pellucida, is not only the most abundant species of the subfamily but also the most abundant grasshopper at intermediate montane elevations. And four of our six species of Trimerotropis are limited, as residents, to the mountains.

Camnula pellucida Scudder is a grasshopper of medium size, with clear wings, occurring all the way across southern Canada and south to Virginia, Texas, and California (Helfer, 1963). In our area, however, it is not found below the lower edge of the coniferous forest except as an accidental. It occurs from the lower edge of the foothills to elevations just below timber line, abundant in grassy clearings among the conifers. It feeds almost exclusively on grasses and sedges, though Hilliard (1950) found it feeding on dandelion in cage tests. Because it is limited to the mountains in our area it is not a serious pest, in spite of its abundance, but in southern Canada it may be quite destructive of cereal crops (Riegert et al., 1965).

Large populations at three different altitudes (Stations 2a, 3b, 4a) were studied during the three years of intensive collecting. Our data (summarized in Fig. 19) are adequate for de- termining times of hatching, times of maturing of adults, and period during which adults are present.

10,000'1

/

8,500':,,Z

/

/

6.70o)'

IJune July IAugust Sept.

FIG. 19. Stages in the life cycle of Camnula pellucida in relation to altitude. Stippled: Instars I & II. Hori- zontal lines: Instars III & IV. Vertical lines: Instar V. Black: Adults. Data from Stations 2a, 3a and 3b (pooled), and 4a, in 1959 and 1960. Total specimens: 914 juveniles, 945 adults. See Putnam (1963) for relative lengths of time in the juvenile stages. The broken line indicates projected seasonal delay (Hopkins, 1919). (See DISCUSSION.)

Hatching at 6,700 ft begins in mid-May and continues into the third week of June, at which time all juvenile instars are present simultaneous- ly. Hatching at 8,500 ft occurs from about June 1 into July; and, at 10,000 ft, it is from mid-June to mid-July. Adults appear at 6,700 ft during the first week of July, at 8,500 ft in mid-July, and at 10,000 ft during the last week of July. They are present into September at all these altitudes and may be numerous even as late as mid-Sep- tember. The highest elevation at which we collected Camnulc-just below timber line on Mt. Evans (10,800 ft)-is the location of a small resident population, adults maturing about the first of September.

Several accidentals of Camnula were taken at elevations below the resident range. Every year a few adults were collected at Chautuaqua Mesa, which is just a hundred feet or so vertically, and less than a half mile horizontally, from the lower edge of the resident range. In 1960, 12 adults were collected at that station between July 7 and August 11.

Specimens of Camnula pellucida collected in our area, 1958-1960: 1,452 juveniles, 1,343 adults.

Circotettix rabula rabula Rehn & Hebard is the largest and noisiest of the aerial "cracklers" in our mountains. A mixed feeder, according to Brooks (1958), it is most frequent in gravelly clearings among the pines from about 6,500 ft up to timber line. It does not occur, in spite of strong flight, outside altitudes at which it is resident. Though distributed from Arizona and New Mex- ico north into Canada we have not found it below our foothills. Individuals tend to be reddish at lower elevations (where the soil is derived from reddish sedimentary deposits) and gray at higher elevations (on a gray granite substratum), but variations among populations of this species have frequently been commented upon elsewhere. We find no evidence for the differences recognized by Rehn (1921) in describing a subspecies from the higher altitudes (C. r. altior), though specimens from our area were included in his original series.

Circotettix is most abundant at intermediate montane elevations, above 8,000 ft, so our records from Station 2a are fewer than from higher altitudes. Hatching at 6,700 ft takes place in late May and in June; at 8,500 ft, after the first of June; and, at 10,000 ft, near the end of June. According to our observations, adults appear at 8,500 ft by early in July, and not much later at 10,000 ft. Adults are present through September at all these altitudes. The highest resident population we found was at timber line on Mt. Evans




(10,800 ft), where dates were about the same as at 10,000 ft.

Specimens of Circotettix rabula collected in our area, 1958-1960: 156 juveniles, 267 adults.

Cratypedes neglectus (Thomas) is a robust form superficially like Xanthip pus corallipes leprosus but darker and more uniform in coloration. It is widely distributed in the west, where it may occur in open habitats (Hewitt & Barr, 1967), but in our area it occurs only in small clearings in pine forest from the lower edge of the pines to about 8,500 ft. We have taken it in large numbers at Stations 2b and 3a, where there is little open ground, but rarely at Station 3b, which is an extensive open area. Its ecological distribution is thus like that of Trimerotropis cincta, and in contrast with that of Xanthip pus. It overwinters in the egg stage, hatching during the last part of May and first of June at 6,700 ft and in June at 8,500 ft. Adults appear at 6,700 ft by the last week of June and at 8,500 ft by mid-July. They survive into September.

Specimens of Cratypedes neglectus collected in our area, 1958-1960: 69 juveniles, 364 adults.

Trirnerotropis campestris McNeill is relatively scarce in our area. We have found it confined to clearings in the forest from the lower edge of the pines to about 9,500 ft. It is apparently resident, though we have collected very few juveniles that could definitely be assigned to this species. (It is difficult to assign early instars of Trimerotropis to a particular species.) Adults have been found as early as the second week of July and as late as early October.

Trirnerotropis cincta (Thomas) is a dark, slender species of fairly wide distribution in the west. We have found it primarily in close association with the pines, as is Cratypedes, and common only in small clearings. Its resident range in our area is from about 6,000 to 10,000 ft in altitude. We have taken a few accidentals at Chautauqua Mesa, a short distance below its resident range.

Hatching begins at 7,200 ft by June 1 or earlier; at 8,500 ft by the second week of June. Adults appear at Station 2b in the third week of July and at 3a the first week of August. Adults are most abundant at both stations through August and the first half of September.

Specimens of Trimerotropis cincta collected in our area, 1958-1960: 107 juveniles, 184 adults.

Trimerotropis humile (Morse) is presumably limited in geographic distribution to the mountains of Colorado. It is relatively uncommon in our area, but is resident from the lower edge of the

foothills to 8,500 ft or a little higher-more common at lower elevations, and more likely to appear in open areas than among the trees. The few juveniles collected suggest that it hatches in late June or early July. We have collected adults through August and into September.

Trimerotropis suffusa Scudder is a dark species, with wing tip suffused with black, that occurs through the Rockies from Arizona and New Mexico north into Canada, and in the western ranges from California to British Columbia. In our area it is present only in clearings in the coniferous forest from its lower edge to timber line, apparently resident throughout this altitudinal range. In other parts of its range, however, it occurs in sagebrush (Hewitt & Barr, 1967).

Juveniles taken at Stations 2b and 3a indicate that hatching occurs during the first half of June at 7,200 ft and about a week later at 8,500 ft. Adults appear at both stations by the third week of July, and adults are present at Station 4a by the first week of August. They are present into mid- September.

Specimens of Trimerotropis suffusa collected in our area, 1958-1960: 39 juveniles, 159 adults.

ACRIDIDAE: GoMPHOCERINAE

This subfamily, as interpreted by Uvarov (1966a), comprises those species included in the Acridinae in previous papers on Colorado Orthop- tera (Hebard, 1929; G. Alexander, 1941). It is more restricted than the Acridinae of Rehn and Grant (1960), who combined the genera of this subfamily with the Oedipodinae under the name Acridinae. Members of the subfamily are generally small, most of them have a "retreating face," and they have a stridulating mechanism that in- volves the hind femur and tegmen. The species are primarily grass feeders, and we find large populations only in areas of grasses and sedges. No species in this group is an economic pest in our area, though a few are so considered in pastures further north.

There are 20 species in the following account, 19 from our restricted area and one, Bruneria brunnea, represented by a small nearby population (in Rocky Mountain National Park). Individual species are treated under distributional categories but the altitudinal ranges of all are summarized in Table 5.

On Plains Only. Ten species of Gomphocerinae are apparently limited as residents to the plains, occurring no higher in the Boulder region than about 5,800 ft. No one of these species is very




TABLE 5. Altitudinal distribution of the Gomphocerinae of the Boulder region. Altitudinal bands are in 103 ft. R, resident; A, accidental.

5-6 6-7 7-8 8-9 9-10 10-11 11-12 >12

A crolophitus hirtipes R A A A Aeropedellus clavatus R R R R R R R R Ageneotettix deorum R R R A A A A Amphitornus

coloradus R R R A A A Aulocara elliotti R A A A A A A Boopedon nubilum R A Bruneria brunnea R Chloealtis conspersa R? R Chorthippus

curtipennis R R R R R R R Cordillacris

occipitalis R Drepanopterna

femoratum R A Eritettix simplex R R R R Mermiria

maculipennis R R M. neomexicana R Neopodismopsis

abdon.inalis R R R R R R Opeia obscura R Orphulella pelidna A? A A A 0. speciosa R Phlibostroma

quadrimaculatum R Psoloessa delicatula R R

common in our area, even at lowest elevations, though some are quite common several miles further east.

Acrolophitus hirtipes (Say) is a large species, contrasting in several ways with "typical" members of this subfamily. It feeds predominantly on forbs (Boraginaceae, according to Brooks, 1958, but we found it associated principally with Phace- lia). It takes flight readily and flies well but leisurely. This flying behavior, with its prominent (yellow) wings, makes it quite conspicuous; and since adults are not easily overlooked we assume it is actually less abundant than other, less conspicuous species. This view is supported by the fact that we collected many more adults than juveniles. All juveniles (and all adults collected during 1958-1960) came from Station la. Hatch- ing there (5,450 ft) is from late May into June; adults occur from the first week of July into Sep- tember. A few accidentals have been taken, one as high as 9,500 ft.

Specimens of Acrolophitus hirtipes collected in our area, 1958-1960: 22 juveniles, 125 adults.

Aulocara elliotti (Thomas), a common, destructive species in short grass pastures of the west (Pfadt, 1949) is less abundant in our area than a few miles further east. It is resident only below the lower edge of coniferous forest, but it is a strong flier and has appeared as an accidental even above timber line (G. Alexander, 1964). Hatch-

ing at 5,100 to 5,500 ft is through June into July; adults are present in July and August.

Specimens of Aulocara elliotti collected in our area, 1958-1960: 30 juveniles, 72 adults.

Boopedon nubilum (Say) is rare in our area and of quite local distribution. Several were collected in 1949 in the pasture north of Boulder, juveniles from mid-June through July and adults through August. One specimen, a fourth instar juvenile, was collected at Station la in July, 1959. One accidental, a typical jet-black male, was collected at 7,500 ft, in August, 1949.

Cordillacris occipitalis (Thomas), a tiny grasshopper, associated with short grass habitats of sparse herbiage, is fairly common at White Rocks (5,100 ft), where we made occasional collections. This is near its upper altitudinal limit in our area as it is rare even as high at 5,700 ft. Hatch- ing occurs from the last of May through mid-June; adults appear before the end of June and are present through August.

Drepanopterna femoratum (Scudder) was rare in our 1958-1960 collections, but more extensive collections in the pasture north of Boulder in 1947 and 1949, and at Valmont Butte in the 1930's, suggest that hatching is in June and July and adults are present through July and August. One accidental was taken at 8,500 ft in 1934.

Mermirica neomericana (Thomas) is much less common, more restricted in local distribution, and a little later in the season than is Mermiria maculipennis, which occurs in the foothills as well as on the plains. Our small collection suggests that this species hatches at Station la about the end of June or first of July; adults are present from mid-August into September.

Opeia, obscura (Thomas) is fairly well represented in our collections from grassy areas below 6,000 ft though most specimens collected in 1958- 1960 came from Station la. We have taken no accidentals. Hatching apparently takes place during the last half of June and first half of July; adults are present from mid-July into October.

Specimens of Opeia obscura collected in our area, 1958-1960: 144 juveniles, 255 adults.

Orphulella pelidna (Burmeister) does not seem to be resident in our restricted area, even at lowest elevations, though it is well established a few miles further east. We have taken accidentals several times, however, even as high as 8,500 ft. These, presumably, had flown in from a few miles east of Boulder. (We have taken no accidentals of Orphulella speciosa, which is resident at our lower stations, but 0. pelidna is the species with somewhat longer wings-Gurney, 1940.)




Orphulella speciosa (Scudder), while not common in our area, is well established at Station la and has been collected with fair frequency at Chautauqua Mesa. It has not been taken above 5,750 ft, even as an accidental. Hatching apparently begins about the middle of June; adults are present from mid-July into October.

Phlibostroma quadrimaculatum (Thomas) is uncommon in our collecting area though widespread in short grass habitats of the High Plains. On the basis of limited collections, mostly in the 1930's and 1940's, and especially in the pasture north of Boulder (5,400 ft), we believe that hatching occurs from mid-June to mid-July; adults occur from the second week of July to mid-Sep- tember. The species is resident up to about 5,700 ft; we have taken no accidentals.

On Plains and in Mountains. Eight species of Gomphocerinae, including our most abundant members of this subfamily, comprise this group. Five are plains forms that invade lower elevations in the mountains. The other three are primarily boreal. In our area these three are montane forms that, in two cases, reach the plains only at our highest plains station (5,750 ft). One of these boreal forms, however, Chorthippus curtipennis, ranges, in appropriate habitats, from above timber line to below 5,000 ft.

Aeropedellus clavatus (Thomas), a small species with conspicuously knobbed antennae, and with short wings in the female, has populations in the Boulder area at intervals from 5,700 ft to well above timber line. It is well established up to 13,100 ft on Mt. Evans, the highest resident grasshopper in this part of Colorado. Its alpine populations on Mt. Evans were the basis for the life history studies of the authors (1964).

The success of this species at high altitudes correlates well with its latitudinal distribution, for its range extends north, at lower elevations, as far as Great Slave Lake, Canada (Vickery, 1967). Its southern limits are in the high mountains of New Mexico and Arizona. We have no records of its occurrence below the upper edge of the plains in Colorado, but it is a wide-ranging grasshopper in the plains provinces of Canada. There, according to Brooks (1958), it "is the most widely distributed and abundant of our prairie species, occurring in all dry and somewhat sandy situations south of the forest," and sometimes causing "extensive damage to range grasses." It probably exerts significant pressure on tundra grass and sedge productivity, but we know of no quantitative studies bearing on this.

Though our data on this species are abundant

13,100'

/

/ /

/

8,500'

/~~~~ /~~~~

6,700'r-

5,7 50O'__

i mlay | June | July | August | Sept

FIG. 20. Stages in the life cycle of Aeropedellus clavatitls in relation to altitude. Stippled: Juvenile stages. Black: Adults. Data from Stations 1c, 2a, 3b, and 5c, all three seasons, 1958-1960. Total specimens: 1,344 juveniles, 1,826 adults. (In one recent year, 1963, a few teneral adults were collected at Station lc more than a week earlier than the appearance of first adults indicated on the graph.) The broken line indicates projected seasonal delay (Hopkins, 1919). (See DISCUSSION.)

we can give only approximate dates for different events in its life cycle. This is because hatching dates extend over rather long periods and juveniles of several instars and adults are collected together (Fig. 20). Hatching at 5,750 ft begins in late April and continues through May; at 6,700 ft. it is only a little later; and, at 8,500 ft. it is from mid-May into. the last half of June. (We found no significant populations between 8,500 ft and timber line.) At 12,800 ft hatching is less than three weeks later than at 8,500 ft. but these eggs have probably been in diapause through two winters (Alexander & Hilliard, 1964). Adults appear at Chautauqua Mesa by the last week of May and at Chicken Ranch Gulch the first week of June; a few are still present in August. At 8,50 ft adults appear during the third week of June and are most abundant in July and August; at 12,800 ft they appear by the third week of July and are in maximum numbers the last half of August. Adults may persist through September at high altitudes even though temperatures often drop well below freezing.

Specimens of Aeropedellus clavatus collected in our area, 1958-1960: 2,984 juveniles, 3,870 adults.

Ageneotettix deorum (Scudder) is the most




abundant member of this subfamily at our plains stations. Its geographic range is from Mexico into the prairie provinces of Canada. Its altitudinal range in our area, as a resident, extends up to 7,200 ft, with accidentals at higher montane elevations-even above timber line (G. Alexander, 1964). Its abundance drops off sharply at our upper plains stations: In 1959, of 788 juveniles collected only 103 were from above 5,750 ft; and of 585 adults collected only 104, including several accidentals, were taken above 5,750 ft. The delay in life cycle related to altitude is quite striking, for adults are abundant at 5,400 ft before the first ones appear at 6,700 ft. Since the species in a mixed feeder, even feeding on debris (Brooks, 1958), this relation to altitude does not have a biotic basis. The excessive delay is perhaps related to the fact that the species is probably near its limit of tolerance, climatically.

Hatching at 5,400 ft occurs from the third week of May to mid-June; at 5,750 ft, slightly later; and at 6,700 ft, from late May or early June to about July 1. Adults appear at 5,400 ft by the last of June; at 5,750 ft, by July 7; at 6,700 ft by mid-July. Adults are still present in October.

Specimens of Ageneotettix deorum collected in our area, 1958-1960: 1,671 juveniles, 1,175 adults.

Amphitornus coloradus (Thomas) is not distributed so far north in latitude nor so high in altitude as is Ageneotettix deorum, so it is not surprising that is is common in our area only up to 5,400 ft, is scarce even at 5,750 ft, and rare, as a resident, above that altitude. In 1960: Of 437 juveniles only two were collected at 5,750 ft or above; of 359 adults only seven were from 5,750 ft or higher. Our highest record for a juvenile was 7,600 ft. It is definitely a plains species, barely invading the foothills, though occurring as an accidental even above timber line (G. Alex- ander, 1964).

Hatching at Station la is from mid-May to mid- June (though we collected a second instar juvenile on Aug. 31, 1960, suggesting the possibility of a second brood) ; adults appear by the end of June and are abundant after mid-July and in August.

Specimens of Amphitornus coloradus collected in our area, 1958-1960: 733 juveniles, 530 adults.

Chloealtis conspersa Harris is a rather scarce, short-winged species associated with forested areas but feeding chiefly on grasses and sedges. It oviposits in wood. A few juveniles from Chautau- qua Mesa suggest that it is resident below 6,000 ft -but recent collections are chiefly from Chicken

Ranch Gulch (6,700 ft). There it hatches about June 1 and becomes adult about a month later.

Chorthippus curtipennis Harris may be the most widely distributed grasshopper, altitudinally, in Colorado. It occurs over practically the whole of the United States, and its range extends north into northern Canada and northern Alaska (Vick- ery, 1967). It is characteristic, in our area, of moist sedge or rush areas at all altitudes up to a little over 11,000 ft.

Our collections during 1958-1960 were chiefly from a roadside ditch south of Valmont Butte (5,100 ft), a wet meadow near Science Lodge (9,500 ft), and Station 4d on the Rollins Pass road (11,200 ft). At 5,100 ft hatching occurs through June; at 9,500 ft, mid-June to mid-July; and at 11,200 ft, through July. Adults appear at 5,100 ft by mid-July; at 9,500 ft, the last week of July; and at 11,200 ft, early in August. They persist at the higher altitudes through September.

Specimens of Chorthippus curtipennis collected in our area, 1958-1960: 410 juveniles, 472 adults.

Eritettix simplex (Scudder) is represented in our area by the subspecies E. s. tricarinatus (Thomas). This grasshopper hatches late in the summer, overwinters as a juvenile, and matures early the following spring. (See Fig. 21 for age distribution throughout the season.) The juveniles can survive freezing (G. Alexander, 1967) and are active in the winter during periods of mild weather. In our area, Eritettix is resident on the plains and up to 8,500 ft-perhaps a little higher. (In latitude, it ranges from Texas into southern Canada.) Hatching begins about the middle of August at all elevations from 5,400 to 8,500 ft and continues about a month. There is little evidence of any delay in hatching time correlated with altitude.

8,500' Juveniles Adutts & Eggs / Juv's

0,9 0 ' Juveniles Adults a Eggs Juv's

5,600 ' Juveniles Adults a Eggs Ju is

| Feb I Mch I Apr I May June | July I Aug I Sept I Oct

FIG. 21. The life history of Eritettix simplex tricarinatus at different altitudes. The observations on which this is based are from Stations la and lc (mean altitude shown), 2a and 2b (mean altitude shown), and 3a and 3b. Data were pooled for each pair of stations. Total specimens: 91 juveniles, 724 adults. Note that hatching time, soon after mid-summer, is independent of altitude.




Most individuals of Eritettix are in the third instar at the onset of winter. The next two molts occur during intervals of mild weather, with the result that last (fifth) instar juveniles begin to appear by the first of March below 6,000 ft and by the end of that month at 7,600 ft. The final molt may occur below 6,000 ft as early as the first week of April; but, at 6,700 ft, adults do not appear until the second week of May, and, at 8,500 ft, about the last of May. Males typically mature earlier than females. We collected no juveniles, at any station, in June, July, or the first half of August, but adults were present at all stations during this period.

This pattern of life history in grasshoppers, overwintering juveniles, has recently been re- viewed comprehensively by Uvarov (1966b).

Specimens of Eritettix simplex collected in our area, 1958-1960: 137 juveniles, 865 adults.

Mermiria maculipennis Bruner, our subspecies being M. m. macclungi Rehn, is associated with tall grasses. Unlike its scarcer relative, M. neomexicana, this form is resident in the foothills as well as on the plains, occurring regularly, though in small numbers, up to 6,700 ft. We have collected it no higher, even as an accidental.

At Station la hatching begins about June 1 and continues several weeks. The season is about a week later at Station ic and begins about July 1 at Station 2a. Adults appear at Station la by mid-July; at Station ic by late July; and at Sta- tion 2a about the second week of August. Thus there is considerable delay correlated with altitude.

Specimens of Mermiria maculipennis collected in our area, 1958-1960: 299 juveniles, 211 adults.

Psoloessa delicatula (Scudder) is so scarce in our area that we have little information about it. It is a member of the small group of species that overwinter as juveniles rather than in the egg stage (Uvarov, 1966b). Adults have been collected in the creek bottoms east of Boulder as early as the middle of April, and at Chicken Ranch Gulch as early as June 9. We have taken several juveniles in the spring but only one in the fall (November). The species apparently ranges in the Boulder area from the plains up to 6,700 ft.

In Mountains Only. Only two species of Gom- phocerinae are in this category, and one of these has not been collected in our transect but occurs a few miles to the north.

Bruneriac brunnea (Thomas), a boreal species that reaches its southern limits in the mountains of Colorado, is of hypothetical occurrence in our area. It occurs in isolated, relict populations in various parts of the Colorado Rockies, both south

and north of our area, and one such population is only 18 miles north of our transect, at 8,300 ft, in a grassy meadow in the Horseshoe Park section of Rocky Mountain National Park. Hatch- ing occurs there from mid-June to mid-July, and adults are present by the first of August.

Neopodismopsis abdominalis (Thomas) is similar to its locally scarcer relative, Chloealtis conspersa, in habitat preference but has a more boreal distribution, occurring as far north as northern Canada and northern Alaska (Vickery, 1967). In our area we find it from 6,700 ft to timber line, though it is more common above 8,000 ft than below. It occurs in small clearings in the forest, where it feeds on grasses. It lays its eggs in dead wood.

Hatching at 6,700 ft begins about the second week of June; at 8,500 ft, almost as soon; at 10,000 ft, soon after mid-June; and at 11,000 ft, the first week in July. Adults appear at 8,500 ft and below by the third or fourth week of July and at 10,000 and 11,000 ft by the first week in August. It is apparent that increasing altitude has little effect on delaying development in this species.

Specimens of Neopodismopsis abdominalis collected in our area, 1958-1960: 255 juveniles, 123 adults.

TETTIGONIIDAE

The family Tettigoniidae is represented in the Boulder region by eight species. The meadow grasshoppers are moderately common in grassy areas on the plains but invade the mountains only at lower elevations. One decticid, Anabrus simplex, is the only species that occurs as high as the alpine tundra. All our Tettigoniidae are probably predators as well as herbivores, and this statement applies to the small meadow grasshoppers (Isely & Alexander, 1949) as well as to the decticids.

Anabrus simplex Haldeman occurs over much of the west, from Arizona into Canada. It has been particularly destructive in the Great Basin, where it acquired the name "Mormon cricket." During outbreaks it feeds on all types of vegetation, even including pine needles, as well as on insects (Swain, 1940).

In our area Anabrus has small but well developed populations in clearings in the lower montane forest between 6,500 and 7,500 ft altitude. It appears again at timber line but seems to be absent from intervening montane elevations. It is locally present in fairly large numbers in the tundra even to above 13,000 ft. Hatching in the lower montane population takes place during the last half of May and in early June. In the popu-



416 GORDON ALEXANDER AND JOHN R. HILLIARD, JR. Ecological Monographs i ~~~~~~~~~~~Vol. 39, No. 4

lations from 11,200 to 12,800 ft this is during the third week of June. Adults appear by mid-June in the lower populations, by the third week of July in the alpine populations. They persist into Sep- tember even at the higher elevations.

Specimens of Anabrus simplex collected in our area, 1958-1960: 369 juveniles, 243 adults.

The small meadow grasshoppers of the genus Conocephalus are represented by three species, two of these moderately common at the upper edge of the plains and all three occasionally present, and apparently resident, in the lower foothills. Early juveniles were difficult to associate with a particular species, so we recorded some 250 early juveniles only as Conocephalus sp. Dates of appearance of late juveniles and adults, however, suggest that all three species hatch early in June, mature by the third week of July, and are present through August into September.

Conocephalus fasciatus (DeGeer), the least common of the three local species, has been collected chiefly on the plains east of Boulder, but it has also been collected at Chautauqua Mesa, both as juvenile and adult. A few adults, including short winged individuals, have been collected in the lower montane region, so it is possible that this species is resident, rarely, up to 8,500 ft.

Conocephalus saltans (Scudder) appeared regularly at Stations la and ic, where adults occur through late July and all of August. It is also resident though less common at 6,700 ft. A long winged adult female found at 8,500 ft, Aug. 31, 1959, was undoubtedly an accidental.

Conocephalus strictus (Scudder) was clearly the most abundant member of the genus in the Boulder region. It is common at Stations la and ic, and we have taken both juveniles and adults as high as 6,000 ft on the east side of Flagstaff Mountain. Our only record from a higher altitude was a long winged female, Aug. 25, 1949, at 6,700 ft, probably an accidental. The species is clearly a plains form that barely invades the foothills.

Specimens of Conocephalus strictus collected in our area, 1958-1960: 69 juveniles (plus an un- known number), 168 adults.

Orchelimum concinnum delicatum (Bruner) the name that used by Hebard (1929)-is rare within our area, and we have taken it only below 5,300 ft in meadows. The small number of juveniles and adults taken suggest hatching by mid- June and mature adults by mid-July.

Pediodectes stevensonii (Thomas), distributed on the High Plains from South Dakota to New Mexico, has not been taken by us recently. Adults were occasionally collected in late summer during

the 1930's (and in 1949) on the south side of Valmont Butte. Though probably a predator, this species, in our experience, was closely associated with clumps of yucca.

Scudderia texensis Saussure & Pictet has a well developed population at Chautauqua Mesa and a somewhat smaller one at Station la. It is resident, too, though scarcer, at Station 2a. Hatching at Stations la and ic takes place from the last of May into the second week of June. Adults appear about July 25 and are numerous by the end of July and through August; they persist, occasionally, past mid-September. The smaller population at Chicken Ranch Gulch seems to be about ten days later.

Specimens of Scidderia texensis collected in our area, 19,58-1960: 365 juveniles, 212 adults.

Steiroxys trilineatus (Thomas) was recorded from New Mexico to Montana, west to Utah and east to Nebraska, by Caudell (1907), but Hebard (1929) believed, probably rightly so, that it is limited to the Rockies from Colorado to Montana. It is a late summer decticid, found only in open areas in pine forest at intermediate elevations. All our records are within an altitudinal range of approximately 8,000 to 9,000 ft. During 1958- 1960 we collected only 11 juveniles and three adults, all at Station 3b. Hatching occurs as early as the first half of June, but our only adults during those years (all females) were collected after the middle of August.

GRYLLACRIDIDAE

Only one species of Gryllacrididae, Centho- philus utahensis Thomas, is common in our transect, though we have a single record of C. pallidus from Boulder and one of C. nodulosus Brunner from the foothills at 7,500 ft an unlikely altitude record, though it might be expected near Boulder. Hubbell (1936) reported C. fusiformis Scudder from Golden, only a few miles south of Boulder, and his records suggest that we should find C. alpinus Scudder in our mountains.

While our method of collecting was not adapted for Ceuthophilus we do have a series of specimens taken in pit-falls in 1968 by D. E. Peterson while he was collecting myriapods. These were from near our Stations 2b, 3a, and 4a. All the adults he obtained were of C. utahensis, and we presume the rather numerous juveniles taken were of the same species. These-and our collections from under boards, campground garbage containers, etc.,-indicate that hatching up to 7,000 ft begins in May; at 8,500 ft, in June; and, at 10,000 ft, by early August. Adults were taken at 7,200 ft




from early August into November; at 8,500 ft, in July and August; and, at 10,000 ft, in August. Our highest record is an adult female, taken in a pit-fall at timber line on Mt. Evans, Aug. 18, 1967, by R. R. Schmoller.

GRYLLIDAE

Gryllidae are represented by three species in our area, none at high elevations. Field crickets (Acheta and Nemobius) appear scarcer in our collections than they should because our sampling technique was inappropriate for them, but we do have adequate records of tree crickets (Oecan- thus), which are easily taken by sweeping. Amer- ican field crickets placed under the name Acheta assimilis (Fabricius) represent numerous taxa (R. D. Alexander, 1957), as do those under the name Nemobius fasciatus (DeGeer) (Alexander & Thomas, 1959), but we use these names because little is yet known of their western components. We use Acheta, too, though the genus may properly be Gryllus (Randell, 1964).

Acheta assimilis is common and widely distributed about Boulder up to about 7,000 ft. Adults have been collected from early June into early October; juveniles, from the last week of July into the first half of May. Juveniles apparently overwinter.

Nemobius fasciatus is not at all common in our area, but we did collect several juveniles a few miles east of Boulder, July 16, 1958. We have one record of an apparent accidental, an adult female at 9,500 ft, Sept. 10, 1949.

Oecanthus nigricornis quadripunctatus Beuten- muller is our only tree cricket. This widely distributed form is said to grade into 0. n. argentinus

Saussure in the west (Helfer, 1963) but we found no specimens suggesting that. All ours, including juveniles, had antennal markings characteristic of quadripunctatus. This form was common at Stations la, ic, and 2a, in vegetation, where it feeds on floral parts (including pollen), organic debris, and probably small insects (Gangwere, 1961). It is resident up to above 7,000 ft, and we have adults, presumably accidentals, from 8,500 and 10,000 ft.

Hatching occurs at Stations la and ic about mid-June, and, apparently, about two weeks later at 6,700 ft. Adults appear at the upper plains stations by the third week of July, are at peak abundance in late August, and are present until mid-September; the earliest adults at Station 2a were taken after August 1.

Specimens of Oecanthus nigricornis quadripunctatus collected in our area, 1958-1960: 231 juveniles, 247 adults.

DISCUSSION

ALTITUDINAL ZONATION

An altitudinal gradient is quite obviously reflected in the distribution of Orthoptera in the Rocky Mountains. There is, for example, a pronounced decrease in the number of species as one ascends the mountains, and this decrease is reflected even in 1,000-foot altitudinal bands (Table 6) arbitrarily set up to ignore suggested boundaries between altitudinal biotic zones. The alpine tundra has fewer than one twentieth as many resident species as does the high plains.

There are elevations in this gradient where the drop in number of species from one altitude band to the next one higher is more pronounced than

TABLE 6. Numbers of species of Orthoptera (s. lat.) that maintain resident populations in the Boulder region within each 1,000-foot range in altitude. (The Gryllacrididae are omitted because we consider our collections of these inadequate.)

Altitude in 103 ft above sea level

Total 5-6 6-7 7-8 8-9 9-10 10-11 11-12 12-13

Mantidae .......................... 2 2 1 1 Phasmidae ......................... 1 1 1 Tetrigidae .......................... 4 2 2 2 2 2 1 Acrididae:

Romaleinae .....................1.. 1 Cyrtacanthacridinae . ..... . . . . . . . . .1 I I Catantopinae ..................... 25 19 12 9 8 7 6 4 1 Oedipodinae ................. ..... 26 18 16 13 9 7 5 1 Gomphocerinae ................... 19 17 9 6 5 3 3 3 1

Tettigoniidae ....................... 8 6 5 2 1 1 1 Gryllidae ..... .............. 3 3 2 1

Totals ............................. 90 71 49 34 25 19 15 9 3

Per cent drop in numbers of species ... 30% 30% 26% 24% 21% 40% 67%




elsewhere, suggesting the possibility of zonal boundaries, but the reduction in species numbers per 1,000-ft band is surprisingly great all along the gradient. These differences in species numbers do not in themselves, of course, give us an adequate basis for recognizing zonal boundaries. But, by comparing distribution patterns of the individual species with suggested altitudinal biotic zones we can determine the appropriateness or use- fulness of a zonal classification for the altitudinal distribution of Orthoptera. When we do this we can, depending upon our predilections, demonstrate correlations between Orthoptera distribution and (1) major altitudinal zones previously recognized, (2) these same zones plus certain prominent ecotonal regions, or (3) a gradient that is little more than a continuum of overlapping ranges. Analysis of orthopteran distribution does provide support for zonal classification schemes, with, even, "index species" for certain zones. At the same time this analysis points up some short- comings of such schemes.

The pattern of altitudinal zonation in the Colo- rado Rockies was recognized over 50 years ago with two different sets of terms. There are no fundamental differences, however, except in terms, between these. Ramaley's 5 plant zones (1907) and Merriam's life zones-as interpreted for Colorado by Cary (1911)-were both characterized by dominant vegetation patterns or dominant plant species. Subsequent modifications of these zonal classifications have been proposed, but none has differed greatly from these previous schemes except in terminology. And the different terms used generally involve names of characteristic plants, as, in fact, was Merriam's original practice in naming the life zones of the San Francisco Peaks, Arizona (1890). Suggested increases in the number of zones are appropriate south of our area but not in the Boulder region. There have been sug- gestions that only 3 rather than 4 zones should be recognized above the plains. See Gregg (1963) for a detailed summary of the various schemes of altitudinal zonation proposed for Colorado.

Marr, in his description of the ecosystems of the Front Range of the Colorado Rockies (1961) along the same transect used in the present study -recognized 8 "regional ecosystems" above the plains. Four of these were climax regions: Lower Montane Forest, Upper Montane Forest, Sub- alpine Forest, Alpine Tundra. The other 4 were ecotones: Grassland-Lower Montane Forest, Low- er Montane Forest-Upper Montane Forest, Upper Montane Forest-Subalpine Forest, Subalpine For- est-Alpine Tundra. If to these we add the Grass-

TABLE 7. Distribution of all common and *abundant species of Acrididae in relation to the altitudinal regions recognized by Marr (1961): 1. Grassland, < 5,600 ft; 2. Grassland-Lower Montane ecotone, 5,600-6,000 ft; 3. Lower Montane Forest, 6,000-7,700 ft; 4. Lower Montane-Upper Montane ecotone, 7,700-8,000 ft; 5. Upper Montane Forest, 8,000-9,000 ft; 6. Upper Montane-Subalpine ecotone, 9,000-9,300 ft; 7. Subal- pine Forest, 9,300-11,000 ft; 8. Subalpine-Alpine ecotone, 11,000-11,400 ft; 9. Alpine Tundra, > 11,400 ft. (X = Resident in indicated altitudinal range.)

Species 1 2 3 4 5 6 7 8 9

Romalaeinae: Brachystola magna ... x x

Catantopinae: Aeoloplides turnbulli . x

*Hypochlora alba. ... x x

*HesperotettaX virndis ssp.. . x x x

Melanoplus femurrubrm .... x x x M. keeleri . . x x x

*Phoetaliotes nebrascensis x x x

*Melanoplus bNvittatus ...... . x x x x x

*M. confusus . . . x x x x x

*M. packardit . .. ... x x x x x

*M. sanguinipes ...... x x x x x x

M. dawsoni. . . . x x x x x x

*M. dodgei. ....X X X X X X X

*M. fasciatus x x x x x x

M. alpinus . x

M. borealts ... x x

M. marshall x x x

Cedipodinae: Hadrotettix trifasciatus . .... .. x Mestobregma platte. x Arphia pseudonietana .x x x

Trachyrhachis kiowa . .. . ....... ... x x x *Arphia conspersa ....... . x x x x x x x

*Xanthippus corallipes ssp.. x x x x x x

Cratypedes neglectus .. x x x

TCamnula pellucida ... . .........x x x x x

Circotettix rat1ula. . . . . . x x x x x

Trimerotropis cincta. . . x x x x

T. suffusa. . . x x X X X

Gomphocerinae: Aciolophitus hirtipes. x

Opeia obscura. .x x

*Ageneotettix deorum .x x x

*Amphttornus coloradus .x x x *Eritettix simplex ......... ...... . x x x x x

TChorthippus curtipennis .. x x x x x x x x x

*Aeropedellus clavatus . .x x x X X X X X

Neopodismopsis abdominalis .. . x x x x x x

land climax we have 9 altitudinal regions: 5 climax regions, which correspond approximately with Ramaley's (1907) Plains, Foothills, Montane, Sub-Alpine, and Alpine Zones, and 4 ecotones. (Ramaley did not recognize the ecotones in his classification, so altitudinal ranges given for these two patterns do not correspond exactly.)

We have summarized in Table 7 the distributions of 36 species of Acrididae in relation to these 9 altitudinal regions, using the altitudinal ranges provided by Marr (1961). These 36 species are those grasshoppers that were collected in largest




numbers during 1958-1960. We shall refer to them as ''common"~ or "abundant,'" arbitrarily calling a species common if more than 100 specimens were collected during 1958-1960, abundant if more than 1,000 specimens were collected during the period. (Throughout the DISCUSSION section we shall be dealing primarily with these species in the common or abundant categories; abundant species will be indicated by an asterisk preceding the scientific name. Species will be listed in the order in which they appeared in RECORDS OF INDIVIDUAL SPECIES.)

The figures in Table 6 (which includes uncommon as well as more common species) indicate that nearly 80% of the resident species in the Boulder region occur below 6,000 ft. Most of these are regular members of the high plains fauna, occurring below 5,000 ft as well as in the range 5,000 to 6,000 ft and extending upward in range to various altitudes. It is the upper limit of distribution of these species that provides much of the evidence for altitudinal zonation. A few species are limited to the mountains; with these, lower limits of distribution as well as upper limits may be significant.

Examination of Table 7 reveals both types of species among the more common ones. There are species of the Grassland Region that reach no higher than the upper edge (Grassland-Lower Montane Forest ecotone'): Brachystola magna, *Hypocjlora alba, Opeia obscura; and species of the mountains that reach no lower than the same ecotone: *Melanoplus dawsoni and *Aeropedellus clavatus. When we combine these distributional features with the observation that numerous species are limited to altitudes below 5,600 ft, including Aeoloplides turnbulli, Hadrotettix trifasciatus, Mestobregma haydenii, and Acrolophitus hirtipes, as well as less common species, we find good evidence for the reality of the Grassland Region and its upper ecotone.

Evidence from distribution of Acrididae for the existence of some kind of lower montane region is also strong, though no species is limited to that region; and our evidence suggests that it is not necessarily a distinct region but can as easily be interpreted as part of the ecotone between grassland and montane forest. Eight species listed in Table 7 reach their upper altitudinal limits in this region: *Hesperotettix viridis, Melanoplus femurrubrum, M. keeleri, *Phoetaliotes nebrascensis, Arphia pseudonietana, Trachyrhcachis kiowa, *Age- neotettix deorum, *Amphitornus, coloradus; and 8 species from higher altitudes reach their lower limits here: *Melanoplus dodgei, *M. fasciatus,

Cratypedes neglectus, *Camnula pellucida, Circo- tettix rabula, Trimerotropis cincta, T. suffuse, Neopodismopsis abdominalis. When we characterize a region in this way, i.e., by large numbers of species invading it from opposite directions but not extending in range across it, we may properly call it an ecotone rather than a distinct region. And in this particular case 16 species in the total fauna of 26 fall into the general category of invaders, there reaching upper or lower limits. It thus appears that in so far as orthopteran distribution is concerned the Lower Montane Forest might be considered a part of the ecotone of grassland and montane forest.

We are not surprised, of course, to find no evidence for an ecotone involving Orthoptera between the Lower and Upper Montane Forest Regions. No species reaches either upper or lower limit in this altitudinal range (column 4 in Table 7). We find it almost equally difficult to characterize the Upper Montane Region as such. There are 18 species in this altitudinal range. All of these occur also in the Lower Montane, and 12 of the 18 extend into the Subalpine Forest Region. But 5 of the invaders from lower altitudes range all the way up from the plains. Perhaps it is significant that this is their upper limit. We could thus characterize the Upper Montane Forest Re- gion as that region in which the following Acri- didae reach their upper resident limit: *Melano- plus bivittatus, *M. confusus, *M. packardii, *Xanthippus corallipes (the subspecies X. c. leprosus), and *Eritettix simplex. On the other hand, since all 18 species of this altitudinal range are also found in the Lower Montane Forest, and since 18 of the 27 species in the Lower Montane are also found in the Upper Montane, we can question the basis for recognizing any distinction between Upper and Lower Montane regions. And to support the possibility that the montane region should be considered a single zone we have one species whose range extends only through Lower and Upper Montane regions, Cratypedes neglectus.

On the other hand, the Subalpine Forest Region is as easily characterized by Orthoptera as by other groups-though we find no evidence for an Upper Montane-Subalpine Forest ecotone. Seven species, all rather wide ranging, reach their upper limits in the Subalpine Region: *Melanoplus sanguinipes, *M. dawsoni, *Arphia conspersa, *Camnula pellucida, Circotettix rabula, Trimero- tropis cincta, and T. suffusa. (There is a possibility that two of these, the Arphia and the Cir- cotettix, spill over into the ecotone above-column



420 GORDON ALEXANDER AND JOHN R. HILLIARD, JR. Vol. 39, No. 4

headed "8" in Table 7.) Of even more interest is the observation that three boreal species are at their lowest altitudinal limits in the Subalpine Forest Region: Melanoplus alpinus, M. borealis, and M. marshalli. And the first two of these are practically limited to this region, extending upward only into the Subalpine Forest-Alpine Tundra ecotone.

The Subalpine Forest-Alpine Tundra ecotone is the timber line region, which is marked by patches of dwarf timber interspersed with tongues of alpine vegetation. Here we find species associated with the timbered area reaching their upward limits: *Melanoplis fasciatus and Neopodis- mopsis abdominalis. Here also we find species associated with the herbaceous vegetation of open- ings in the subalpine forest reaching their upper limits: Melanoplus alpinus and M. borealis. It is thus a well defined ecotone from the point of view of orthopteran distribution.

The Alpine Tundra Region has five resident species of Acrididae. One of these, *Xanthippus corallipes, is represented by a subspecies (X. c. altivolus) that is limited in our area to the Sub- alpine Forest-Alpine Tundra ecotone and the lower part of the Alpine Tundra Region. One other form, M. marshalli, extends only a little lower in altitude; but the other three, *Melanoplus dodgei, *Chorthippis curtipennis, and *Aero- pedellus clavatuss, have wide altitudinal ranges. (One wide ranging member of the Tettigoniidae, Anabrus simplex, is also a member of the tundra fauna.)

When we review this summary of the altitudinal distribution of the 36 common or abundant species of Acrididae we find that we can characterize four major altitudinal zones, possibly five, and that we do this primarily with combina- tions of species whose ranges reach upper or lower altitudinal limits in the suggested zones. We recognize, too, the existence of two pronounced ecotonal complexes-a group of species characteristic of the region where the grassland of the high plains meets montane forest and another group associated with the contact of subalpine forest and alpine tundra. The large number of plains species reaching their upper limits in the grassland-montane forest ecotone or somewhere in the montane forest, and even the two species that reach the subalpine zone, help provide this characterization. These upper limits are not determined by the types of dominant forest trees, of course, but by available and appropriate clearings in the forest and, presumably, the climatic limits set by a progressively shorter growing season.

The boreal species added to the fauna in the lower montane region and in the subalpine forest provide additional means of characterizing mountain zones. These generally boreal species are presumably intolerant of the high summer temperatures at lower altitudes. The three species occurring only above 10,000 ft belong to the group characterized by Dreux (1962) as stenothermal, ther- mophobic, and perhaps, hygrophilous. (Dreux's studies in the French Alps included extensive comparisons of altitudinal distributions of individual species with data on temperature and hu- midity in July. The major purpose of his study was to examine correlations between distribution and macroclimatic variables.)

In contrast to the three species limited to high altitudes, the more widespread alpine species, *Melanoplus dodgei, *Chorthippus curtipennis, and *Aeropedellus clavatus, are all eurythermal. One, Aeropedellus, is moderately xerophilous, and one, Chorthippus, is definitely hygrophilous. It is interesting to note that species of these two genera observed by Dreux (Aeropedellus vlarie- gatus and Chorthippus longicornis) also show, respectively, pronounced xerophily and hygrophily. It is not surprising, therefore, that our widely distributed Aeropedellus is rare in the moist subalpine zone while Chorthippus is well represented there.

This interpretation of the altitudinal gradient as comprising a series of zones has certain advantages, primarily that of providing a convenient terminology, but the reality of the zones is perhaps more apparent when we consider dominant vegetation than when species of Orthoptera are the point of reference. Even with vegetation we are dealing with "averages," a tree species that forms large stands not being limited to one zone any more than is a species of orthopteran. If one prefers to consider the altitudinal gradient the reflection of a continuum this also may thus be justified from the available data, though the rate of faunal change with altitude is much greater in the transitions between the plains and montane forest and between forest and tundra than elsewhere in the gradient.

As pointed out at the beginning of this section, there is a rather rapid drop in numbers of species of Orthoptera with increasing altitude. This decrease is at a much steeper gradient than the decrease in numbers of species of flowering plants, as evident from the lists of all flowering plant species associated with the stands analyzed by Marr (1961). (These are listed in Appendix I of his paper; the data here given were extracted




from these lists.) A total of 357 species were collected in all stands. Of these, 169 occurred in the Lower Montane; 159, in the Upper Montane; 147, in the Subalpine; and 103, in the Alpine. Cor- responding numbers of species of Orthoptera from our stations in the same transect were, respectively: 34, 25, 15, and 3. The total decrease in plant species numbers is 40%; that in numbers of orthopteran species, 90%. It is thus obvious that the decrease in numbers of species of Orthop- tera is not directly correlated with the decrease in numbers of species of flowering plants; it is no more due to the decrease in the number of biotic niches than is the decrease in the number of insect species in arctic latitudes (Downes, 1964).

This decrease in species numbers with altitude is undoubtedly related to several components of climate, with one of the most important of these being length of growing season. Evidence has been presented, both in the sections on individual species in this paper and in a previous paper (G. Alexander, 1964), for a fluctuating upper resi- dental limit dependent upon the dates of earliest killing frosts in the fall. This date sets an upper altitudinal limit on numerous plains species, especially any that mature late in the season (e.g., Melanoplus femurrubrum and M. keeleri), but it also sets an upper limit, though a higher one, on early-season, wide-ranging species that are moderately tolerant of low temperatures (e.g., *Melanoplus sanguinipes). On the other hand, those species that maintain populations at high altitudes are necessarily more tolerant of low temperatures, hatching when heavy frosts are still occurring at night, and persisting as adults until extreme cold has eliminated them (Alexander & Hilliard, 1964).

ALTITUDE IN RELATION TO LATITUDE

The decrease in numbers of species with increasing altitude has, of course, its equivalent in a corresponding decrease in species numbers with latitude (Fischer, 1960; Pianka, 1966). Just as in the decrease with altitude, too, this follows a very steep gradient. North America north of 60? N. has only a few more than one-tenth the number of species of Orthoptera known from Arizona.

Though we do not have data on numbers of species at specific latitudes (and such numbers would have to be adjusted to a base altitude), we do have the total numbers of species recorded from several western states in a south-north transect, from southern Canadian provinces, and from North America north of 60? N. These numbers

were derived from Ball et al. (1942) for Arizona; Hebard (1931) for Kansas, Colorado, Montana, and Alberta; Severin (1936) for South Dakota; Hebard (l936c) for North Dakota; Brooks (1958 ) for southern Canadian provinces (Acri- didae and Tetrigidae only); and Vickery (1967) for the region north of 60? N. Minor changes would be necessary to bring some of these figures up to date but the general principle would still be demonstrated.

Numbers of species of Orthoptera (s. str.) recorded from these regions, with the regions arranged in sequence of increasing average latitude, are as follows: Arizona, 196; Kansas, 170; Colo- rado, 165; South Dakota, 151; Montana, 107; North Dakota, 101; Alberta, 80; North America north of 600 N., 22. Brooks (1958) listed 82 species of Acrididae and Tetrigidae from the three prairie provinces of Alberta, Saskatchewan, and Manitoba, south of 540 N. Totals for these two families alone are: Arizona, 145; Colorado, 129; Montana, 90; North America north of 600 N., 21. It is quite apparent that in this geographic gradient the numbers of species of Orthoptera decrease with increasing latitude.

Downes (1964) has pointed out that numbers of insect species decrease more rapidly with increasing latitude than do numbers of plant species. He suggested that the decrease in insect species numbers is not only "more pronounced" but also an "apparently independent phenomenon," when compared with the reduction in plant species numbers. He pointed out the fact that the small number of insect species cannot be due to a shortage of niches. "The arctic environment is not inherent- ly simple and does not forbid a greater diversity, yet. . . It seems to lie beyond the range of physio- logical tolerance of all but a very few." As pointed out in the preceding section, we found a comparable relationship of species numbers with altitude, and we believe the severity of the alpine climatic environment, in particular the short growing season, is the major factor that limits so rig- orously the number of species of Orthoptera at high altitudes. Necessary adaptations to this short season have been evolved by only a few species, e.g., *Aeropedellus clavatus.

It is interesting to compare Vickery's (1967) list of Orthoptera from arctic America with those we found at high altitudes in Colorado. Of the 18 Acrididae known from North America north of 60? N., the following 10 occur on our list of common to abundant forms: Melanoplus borealis, *M. fasciatus, M. femurrubrum, *M. sanguinipes, *Arphia conspersa, *Xanthippus corallipes, *Cam-



422 GORDON ALEXANDER AND JOHN R. HILLIARD, JR Ecological Monographs

nila pellucida, *Aeropedellus clavatus, *Chorthip- pus curtipennis, Neopodismopsis. abdominalis. All of these, with the one exception of M. femurrubrum, have resident populations as high as 10,000 ft in the Boulder region, and six of them as high as 11,000 ft. (M. femurrubrum is represented in the far north, according to Vickery, by two records in southern Mackenzie.) M. borealis, *Chorthippus curtipennis, and *Xanthippus corallipes have all been taken north of the arctic tree line; and, while *Aeropedellus clavatus occurs only as far north as Great Slave Lake, its close relative, A. arcticus, is present even on the arctic slope of Alaska, in arctic tundra. (Vickery, 1967, showed that the northernmost records previously cited for *A. clavatus are of A. arcticus.)

The only alpine or subalpine species in our area not included in Vickery's list of arctic species are Melanoplus alpinus, *M. dodgei, and M. marshalli. These are primarily montane rather than boreal species. The first of these is known, however, from both Montana (where Hebard, 1928, recorded it between 6,000 and 8,000 ft) and Alberta, where it occurs in "montane parklands and grasslands of the foothills" (Brooks, 1958). *M. dodgei is represented both in Montana and the prairie provinces of Canada by M. huroni Blatchley (formerly referred to as M. dodgei huroni)-in forest clearings at intermediate elevations in Mon- tana and at low altitudes in northern Alberta. (M. alpinus is a grass feeder, while M. huroni, like M. dodgei, feeds on forbs.) M. marshalli is a member of a complex of closely related forms represented in southern Montana by the form we have in Colorado but in northern Montana and in Canada by M. oregonensis (Thomas), a close relative.

While striking distributional comparisons can be made between Colorado Orthoptera of high altitudes and those of arctic America, it is equally instructive to compare altitudinal distributions of our mid-montane forms with their distributions in states north of Colorado, and in New Mexico, to the south.

Our montane species that are most abundant in the ecotone where grassland and montane forest meet (*Melanoplus dawsoni and *Aeropedellus clavatus), and which do not occur below 5,600 ft in the Boulder region, are widely distributed at lower altitudes further north. *M. dawsoni occurs over "all of North Dakota" (Hebard, 1936c) and is "widely distributed" in the prairie provinces of Canada (Brooks, 1958). *A. clavatus, also according to Hebard, occurs throughout North Dakota; and Brooks stated that in the prairie

provinces of Canada it "is the most widely distributed and abundant of our prairie species," sometimes causing "extensive damage to range grasses."

South of us, both of these species are limited to mountains, their lower altitudinal limits being even higher than in the Boulder area. *M. dawsoni has been collected as far south as in the Sangre de Cristo Range of northern New Mexico, in under- growth in aspen forest at 9,000 ft, where Hebard (1935) said it was limited to the Canadian zone (= Upper Montane). *A. clavatus has been taken at about 12,000 ft on Wheeler Peak, the highest mountain in New Mexico (a large collection by Donald H. Van Horn, July 23, 1963), and as far south as the Sacramento Mountains, near Cloudcroft, N.M. (Hebard, 1935).

*Camnula pellucida, one of the northern species in Vickery's (1967) catalogue, is perhaps our most abundant montane species. It is widely distributed across the northern states and Canadian provinces, occurring as far north as Dawson, Yukon. It ranges south in the eastern mountains to Virginia and in the Rockies into New Mexico. Though with us it does not occur below 6,000 ft- except as an accidental-it is a common species in range grasslands across North Dakota, Montana, and the prairie provinces of Canada. In New Mexico, on the other hand, even in the northern part of the state, it is confined to elevations above about 8,500 ft (Hebard, 1935).

Relations between altitudinal and latitudinal distributions have already been described for certain pairs of related forms. Thus, *Melanoplus bivittatus is more northern and at higher elevations than is M. differentialis; *Hesperotettix viridis pratensis is more northern and at higher elevations than is *H. v. viridis. Similarly, *Arphia conspersa, which ranges north to about 66' N. (Vickery, 1967), has resident populations to 10,000 ft in the Boulder region, while A. pseudonietana, which ranges only into the southern provinces of Canada south of the forested area, does not have resident populations above our foothills. It is worth noting, too, that in the species pairs in the genera Melanoplus and Arphia the more northern form appears earlier in the season than the southern one. This difference in life history may be significantly tied to latitudinal distribution, species hatching late in the season being poorly adapted for higher altitudes or higher latitudes. (The two forms of Hesperotettix, however, do hatch at about the same time in our area.)

Where we find these correlations between latitude and altitude, climatic factors are probably




of primary importance, but .a suitable biotic habitat is also essential. This is particularly noticeable when we consider the northern distribution of our high plains species that occur no higher than about 6,000 ft. Of the common to abundant grassland forms, Brachystola magna, *Hypochlora alba, Hadrotettix trifasciatus, and Opeia obscura all reach as far north as grasslands of the southern portions of the Canadian prairie provinces (Brooks, 1958). The presence of suitable habitats is undoubtedly responsible in large part for this northern distribution.

Such grassland areas are at much lower altitudes than near Boulder, however, and the climate, at least as reflected in length of growing season, is, in this northern range, not very different from that at 5,500 to 6,000 ft in northern Colorado. Although the Canadian border north of Colorado is at 490, an elevation of 1,900 ft there should correspond, in length of growing season, with Boulder at 5,500 ft (according to the bioclimatic law of Hopkins, 1919). In regions 90 north of Boulder, the length of growing season at 1,900 ft above sea level (3,600 ft lower than Boulder's altitude) should be approximately the same as at Boulder. There are places along the border between North Dakota and Manitoba where the frost-free season is of approximately the same length as at Boulder, though winter temperatures are much lower and summer temperatures are higher (U. S. Department of Agriculture, 1941).

Two common plains species in the Boulder region range further north than we might expect on the basis of climatic variables alone, Aeo- loplides turnbulli and Acrolophitus hirtipes, but both are forbs feeders rather specialized in diet. Presumably they can live in a somewhat more rigorous climate when suitable food plants are available.

It would be desirable to attempt a more exact correlation between altitudinal and latitudinal distributions, but the detailed data for such are not at present available. The statement of Hopkins (1919) that, on the average, 1? latitude northward corresponds with 400 ft of altitude upward serves, however, as a useful point of departure. The season in the mountains at 9,500 ft, which is 4,000 ft above Boulder, should correspond with that at 500 N. Lat., while that in the mountains at 13,500 ft should correspond with that at 600 N.- but the correspondence in each case would be with the northern latitudes at the same altitude as Boulder, 5,500 ft. The elevation of 9,500 ft in our mountains, attained by all species on our list known from north of 600 N. (Vickery, 1967),

should correspond with 600 N. at an altitude of approximately 1,500 ft above sea level, and, of course, most of the collections of Orthoptera from arctic North America have been from below 1,500 ft. In a general way, therefore, we do find excellent correlations between altitudinal and latitudinal distributions.

ALTITUDE IN RELATION TO PHENOLOGY

Just as altitude and latitude have similar effects on distribution, so also are their effects on phenology. As one goes north, or as one ascends a mountain, spring events-such as the last killing frost, the opening of buds, the hatching of insect eggs-are delayed. This delay, according to the bioclimatic law of Hopkins (1919) averages four days for each degree northward in latitude or 400 ft upward in altitude. (See Stemple, 1966, for references to all of Hopkins' papers.)

Seasonal events in the fall are correspondingly hastened, both in the north and at higher altitudes. The first killing frost comes sooner at higher latitudes and higher altitudes. According to the bioclimatic law the season is thus shortened not only by a day at the beginning but also by a day at the end for each 100 ft increase in altitude. The "growing season" available to a species that occurs over a vertical range of 6,000 ft should therefore be shortened, according to this calcula- tion, by 120 days at its upper limit.

Most of the observations previously made on insect phenology in relation to altitude have been in regions without the range in altitude available to us, and they have involved a range of latitude as well as altitude. Mell's (1935) studies on Chinese Lepidoptera were practically all made within an altitudinal range of less than 1,000 m and over the latitudinal range from 23? to 30? N.; Weaver's (1959) report on egg development in spittle bugs involved an altitudinal range on no more than 1,000 ft, with collections from Mary- land to New York, and west to Wisconsin. Hop- kins, however, published records (1919) of brood development of pine beetles near Ashland, Ore- gon, over an altitudinal range of 3,000 ft, and of the opening of spruce buds and the hatching of spruce-gall producing insects over an altitude range of 5,500 ft on Pikes Peak, the latter data more nearly comparable with ours than any other published material we have seen.

The existence of species with an altitudinal range of 6,000 ft or more at the same latitude raises a serious question. How can species like *Melano- plus dodgei, *Aeropedellus clavatus, and *Chor- thippus curtipennis complete their life cycles at



424 GORDON ALEXANDER AND JOHN R. HILLIARD, JR. Ecological Monographs Vol. 3 9, No. 4

high altitudes if their growing season is shortened by 120 days over a 6,000 ft range ? After all, they hatch, mature, and die in one growing season; the adults do not overwinter.

Adults of Aeropedellus appear at 5,750 ft by June 1, which is early in the season for grasshoppers, but at 12,800 or 13,100 ft, where this species has large populations, adults should not appear, according to strict application of the bioclimatic law, before the second week of August (70 to 73 days later than at 5,750 ft). This would leave little time for maturing and egg laying before winter weather, because the first "killing frosts" may be in August. Actually, adults appear at 12,800 ft before the middle of July and even at 13,100 ft before the end of that month. The delay in these life history events is therefore much less than four days per 400 ft of increased altitude. (See Fig. 20.) The delay in seasonal events in the life cycle of *Melanoplus dodgei is also less at high altitudes than projected (Fig. 17).

It is interesting to note that Hopkins (1919) found this same phenomenon of a hastened season at high altitudes for both the spruce-gall louse and the pine beetle. Does this mean that the basic figures of Hopkins are incorrect? Of course, Hopkins stated that these figures represented average delays, but the figures at high altitudes seem consistently to suggest regular departures from the projected delay in the form of a smaller effect at higher altitudes-and later in the season, of course, perhaps another important variable.

There are two possible interpretations of this difference from the projected delay: 1) It is possible that wide-ranging species are made up of populations that are not physiologically (or de- velopmentally) the same at different altitudes (Bey-Bienko, 1965), in which case the high and low altitude populations are not strictly the same. 2) It may be that the delay expressed in the bioclimatic law is not a simple, constant, arithmetical relation but one that varies in its effect as the season progresses-a sliding scale of delay, so to speak, with greater lag early in the season and less by mid-summer. (Weaver, 1959, suggested the possibility that the relationship is exponential rather than arithmetic.) We have evidence for both of these interpretations.

While working with us on the general program, Suanraksa (1960) compared oxygen consumption by individuals of *Melanoplus dodgei and *Aero- pedellus clavatus from low altitude and high altitude populations. The tests were carried out in Boulder. Oxygen consumption at a given temperature, in cc per gram per hour, was signifi-

cantly greater in individuals from high altitude populations than in those from low altitudes. This difference (more striking in males than in females) suggests a definite adaptation for lower temperatures in the high altitude populations: At 210 C, for example, in *M. dodgei males from 6,700 to 8,500 ft the mean consumption of oxygen was 0.28 cc/gm/hr, while in those from 11,000 to 12,100 ft it was 0.51 cc/gm/hr, 80% more. This difference was highly significant statistically. At the same temperature, the mean consumption in *Aeropedellus clavatus males from 5,750 to 8,500 ft was 0.51 cc/gm/hr while in those from 11,000 to 12,800 ft it was 0.70 cc/gm/hr, 36% more. Differences between low and high altitude repre- sentatives were significant to highly significant for males of both species over the whole temperature range of 21? to 41'C; for females these differences were significant to highly significant except at 27? and 31?. There is thus a demonstrated difference between low and high altitude populations in oxygen consumption at a given temperature.

We have already shown (1964) that *Aerope- dellus is also adapted to the short season of high altitudes by an extended diapause in the egg and by an abbreviated life cycle. We have one observation demonstrating extended diapause in *Melano- plus dodgei. Eggs laid by adults collected on Mount Aubudon were buried at ground level at Station C-1 (10,000 ft) on August 29, 1958. Numerous young hatched from these eggs on June 7, 1960, after two winters. Kreasky (1960), working with high altitude species of grasshoppers in the Big Horn Mountains of northern Wyoming, observed two and even three year diapause in the eggs of several species, including three that were in our survey: Melavnoplus alpinus, M. borealis, and Chort hippus longicornis (= *C. curtipennis- Vickery, 1964). Thus it seems probable that even if these high altitude species were subjected to the calculated delay in season they are better adapted to the shorter growing season by having an extended diapause in the egg.

As previously suggested, however, the seasonal delays with altitude, though great, are often not so great as postulated from the bioclimatic law. Hopkins' data (1919) on insect emergence suggest this. His dates of emergence at high altitudes, for both spruce-gall plant lice in Colorado and pine beetles in Oregon, were several days earlier than calculated. Climatic records in our area suggest that this is not merely a biotic phenomenon. The frost-free season is definitely longer at higher altitudes in our transect than




t#000 [

/,000 A -

/00060 _ - 111 -

90005 _

70 00_ _ _ _ _

6000' it 1 (I 6 J/ 15 30 15 30 1* 29 /3 Oct

13

FIG. 22. According to, the bioclimatic law of Hopkins the growing season is shortened with each 1,000 ft increase in altitude 10 days in the spring and 10 days in the fall. The lines in the graph have been projected on this basis from the mean dates of the last frost in the spring and the first in the fall at Boulder (solid line), Denver (long dashes), and Longmont (short dashes). The projected frost-free period at different altitudes is the period between the lines. The actual mean frost- free periods for the weather stations of the Institute of Arctic and Alpine Research are indicated by the horizontal lines with double arrows. It is apparent that the frost-free period at altitudes up to 10,000 ft is essentially as projected, but the period at Station D-1 is about twice as long as projected.

would be expected from theory (Fig. 22). At Boulder, the average frost-free season is 161 days. At Weather Station D-1 (12,300 ft) the length of season as calculated should be only 27 days but it actually averages over 50 days. The season is also somewhat longer than expected at Station C-1 (10,000 ft).

That this is not a general situation, however, is illustrated by weather conditions in a cold- drainage valley almost surrounded by mountains. Fraser, Colorado (Fig. 1), at only 8,500 ft has a frost-free season that averages only 17 days (U. S. Department of Agriculture, 1941). Other valley towns at the same elevation may have longer frost-free seasons than Fraser, but there is much variation depending upon local terrain and exposure. Local conditions are important. Hop- kins suggested that such were at least partly responsible for the differences noted in emergence of western pine beetles at high and low altitudes. In our area, the fact that our high altitude stations generally have east and southeast exposures is undoubtedly a major reason for the hastening of the season at such altitudes. Station D-1, whose frost-free season is indicated in Fig. 22, is on a tundra ridge immediately east of the high range and with no higher elevations east, north, or south

of it. It warms up rapidly in the summer sun, and it does not collect cold air at night from higher areas nearby.

For a few species other than those previously mentioned in this section we have collections over altitudinal ranges of approximately 3,000 ft that also are large enough to permit a rough testing of the applicability of the bioclimatic law. *Melano- plus dawsoni was collected in rather large numbers in 1959 and 1960 at Stations ic, 2a, and 3b. It is fairly easily identified at all stages. We have plotted the earliest dates for various instars at these three stations against altitude (Fig. 16). The variation from the projected lag with altitude (its slope indicated in the graph) is not great. We have done the same for various stages of *Camnnula pellucida from Stations 2a, 3a and 3b, and 4a (Fig. 19). In each case the variation from the expected lag is in the direction already indicated for *Aeropedellus clavatus and *Melano- plus dodgei. This departure is not great, however, and these data illustrate rather than contradict the bioclimatic law.

Our data from species reaching their upper altitudinal limits in the lower montane region or below are, of course, inappropriate for testing the bioclimatic law, chiefly because their altitudinal ranges in our transect are not great enough. Another reason such data are inappropriate, however, is that these species seem to be at their limits of environmental tolerance. Their numbers drop, off sharply at their upper altitudinal limits. (In the cases of *Melanoplus dawsoni and *Caminula pellucida, just mentioned, the altitudinal ranges used were ranges in which the species were abundant throughout. In neither Fig. 16 nor Fig. 19 did we include data from the highest altitudinal ranges of the species.) The lag in appearance of plains species reaching upper limits in the grassland-lower montane ecotone may be as great as one to two weeks for an altitudinal difference of only 400 ft (Brachystola nmagna, *Hypochlora alba, Phoetal- iotes nebrascensis) or a month for an altitudinal range of 1,000 ft (Mermiria caculipennis). To us it appears essential that testing of the bioclimatic law should be restricted to species that are well established throughout the altitudinal range being analyzed.

Another variable that must be considered in analyzing the bioclimatic law is the life history of the species concerned. Seasonal events in the lives of Orthoptera are comparable only among species with the same type of life cycle, preferably a one-year cycle involving overwintering in the egg stage and hatching and maturing during the



426 GORDON ALEXANDER AND JOHN R. HILLIARD, JR. Ecological Monographs i ~~~~~~~~~~~Vol. 39, No. 4

following season. (A few species in our area, judging from limited evidence, may occasionally have two broods in one season, e.g., *Melanoplus packardii, *M. sanguinipes, *Amphitornus coloradus; but this would be a rare variation on the typical pattern in the Boulder region.) We do have, however, radical variations of this pattern. Several species with boreal distribution have two- or even three-year life cycles (Criddle, 1933; Pickford, 1953). The fact that eggs of *Aero- pedellus clavatus do not hatch in the alpine tundra until their second summer (Alexander & Hilliard, 1964) may explain why young juveniles appear at high altitudes before the projected time. A two- or three-year cycle may regularly be characterized by early hatching in the final growing season. Such early hatching would be of survival value for a species subject to a short growing season, one whose distribution is boreal or alpine.

Another important variation on the life history pattern is among the species that overwinter as juveniles (Pickford, 1953; Uvarov, 1966b). These provide one apparent exception to Hopkins' law, as pointed out in our accounts of *Eritettix simplex, *Arphia conspersa, and *Xanthippus corallipes. These species hatch at approximately the same time regardless of altitude. This is not an exception to the bioclimatic law, however, but conforms with an aspect of it frequently overlooked. As one ascends a mountain the season becomes shorter, but it is reduced in length at the end just as rapidly as at the beginning. Fall events occur earlier at higher altitudes, so events that normally occur near the mid-point of the growing season should take place at about the same time at all altitudes. The hatching of juveniles destined to overwinter does take place near the middle of the season-only shortly thereafter -so one should expect the hatch of these three species at approximately the same time at all altitudes, which is the case.

Studies specifically designed to test Hopkins' bioclimatic law, in an area like ours and with material like ours, are desirable; and more critical tests than ours should be carried out. We can say, however, that our studies support Hopkins' findings that a delay in spring events of about four days per 400 ft increasing altitude occurs, and that this delay tends to be less than projected for wide ranging species at their highest altitudes.

ALTITUDE IN RELATION TO SPECIES DIVERSITY AND POPULATION DENSITY

Although our collecting did not give us numbers per unit area, our qualitatively exhaustive tech-

nique did provide a basis for comparing relative population densities as well as species numbers at different altitudes. In the process of locating all species in a particular collecting site at a particular time we collected and recorded all individuals of all species taken. We believe we thus collected individuals (at least of species of Acri- didae and Tettigoniidae) approximately in the proportions in which the different species were represented in the area.

The collections here compared are not defined in terms of absolute area. They are comparable, however, because the size of each collecting site was determined as an area that could adequately be sampled in approximately 45 min. Actually, of course, the areas differed more in character than in size. They differed in plant composition, edaphic features, and climate, necessarily, since they were selected primarily to represent various altitudes. They did, however, have one feature in common. Every area was selected for maximum species diversity at a given altitude. It is not surprising, therefore, that collecting sites not only differed at different altitudes but individually were not uniform; they abundantly reflect what Hutchinson (1959) referred to as the "mosaic nature of the environment."

In the comparisons that follow we use collections as units in spite of the fact that the team of collectors varied somewhat in number. With our collecting method we found little correlation between the number of collectors and the number of species taken. (As a matter of fact, the collection with the largest number of species, 33, made at Station la on Aug. 13, 1959, was made by the two authors, without assistance. The season was significant, however, all collections with maximum numbers of species being made after mid-summer, and most of them in August.

While there was, naturally, some relation between the number of collectors and the number of specimens collected this was less than expected because the largest numbers of individuals were invariably taken early in the season (not later than July), when a large proportion of each collection consisted of juveniles. (The largest collection, 703 individuals taken at Station 2a, July 9, 1959, included 17 species, but 475 of the specimens were juveniles of but three species.)

To eliminate variations that might be related to the number of collectors, as well as to discount effects of variable weather conditions, we have used averages. The mean numbers of species and the mean numbers of individuals collected at each station over the years 1958-1960 are the major




TABLE 8. Numbers of species and individuals collected at representative stations during the seasons 1958, 1959, and 1960. (These figures include accidental species as well as residents.)

Number of species Number of Individuals Number -_ __ Average

Station of Maximum Average Maximum Average Individuals and Col- one per one per per

Altitude lections Total Collection Collection Collection Collection Species

la (5,450') . .44 52 33 20.9 571 273 13.1 lc (5,750') . .41 47 25 16.5 314 153 9.3 2a (6,700') . .45 46 24 15.3 703 193 12.6 3b (8,500') . .35 29 17 11.8 298 113 9.6 4a (10,000') . .32 16 13 6.9 186 65 9.4 4d (11,200') . .8 8 8 6.0 254 131 21.8 5a (12,100') ..... . : ........ 11 7 6 4.5 207 1 28 28.4 5b (12,800') . ............ I 1 4 4 2.9 243 142 48.9 5c (13,100') . .1........... 10 3 3 1.8 284 131 72.8

bases for our comparisons. These, with other perti- nent data, are summarized in Table 8.

When we plot the data having to do with species numbers we get an interesting picture of the relations between species diversity and altitude (Fig. 23). Species diversity is here expressed in three ways. When expressed as the total number of species taken at a given station over the three year period it is greater than when expressed either as the maximum number of species in a single collection or as the mean number of species from all collections at a single station. The relations of these three data at a given altitude are self evident, but the fact that the three figures converge with increasing altitude is perhaps not self evident.

This convergence occurs whether we consider total numbers of species or resident species alone. In Fig. 23 the figures are for totals, accidental as well as resident species. If resident species alone are plotted, the same relations hold but the gradient is steeper, simply because the proportion of

50 -

40 -

430 - <~

i20 - .D 0 ~ -. E+ '10-

5 6 7 8 9 10 1 1 12 13 Altitude in 103 ft

FIG. 23. Numbers of species of Orthoptera in relation to altitude. The data were derived from all collections at Stations la, ic, 2a, 3b, 4a, 4d, 5a, 5b, and 5c during the three seasons, 1958-1960. (These data appear in vertical columns from left to right.) Solid lines (X) = Total number of species taken during the three seasons. Long dashes (+) - Maximum number of species in a single collection. Short dashes (0) =Average number of species per collection. (The actual figures appear in Table 8.)

accidental to resident species increases with altitude (G. Alexander, 1964).

A major reason for the convergence is undoubtedly the longer season at lower altitudes, making possible seasonally different insect faunas -spring, mid-summer, late summer at lower altitudes. In the alpine tundra, in contrast, the season is not long enough for several seasonal types of life histories. The contrast between low and high altitude stations is particularly striking when we consider the distribution of frequencies. At Sta- tion la, where 52 species were taken during the three years, no one species occurred in every collection; but, at Station 5a, three species were present in every one of the 11 collections and, what is more significant, all species with less than 100% frequency were accidentals. (Of course there were more collections at la than at 5a but the entire season was adequately sampled at both.) There were numerous rare species at Station la that were residents, but, if we omit accidentals, none at Station 5a, a situation in which, to quote Hutchinson (1959) "the rare species in a community may be so rare that they do not exist."

In theory, of course, we should reach an altitude above which no orthopteran is found. It is conceivable, too, that at such an altitude only one species is present. There the lines in Fig. 23 representing the total number of species and the maximum number in one collection would converge on a point, the numeral 1. (The average number, of course, may be less than but not greater than one.) Our observations suggest that such an altitude in our area is at approximately 14,000 ft, the highest elevation at which we have collected any species (*Melanoplus sanguinipes, an accidental). We have taken *Aeropedellus clavatus as well as M. sanguinipes at 13,600 ft, and *A. clavatus is there resident. At 13,100 ft (Table 8) three species were collected, and oc-



428 GORDON ALEXANDER AND JOHN R. HILLIARD, JR. Ecological Monographs

casionally all three were taken in one collection. Two of these were resident species, *A. clavatus and the Mormon cricket, Anabrus simplex; the other, of course, was the ubiquitous accidental, *M. sanguinipes.

We believe it is the severity of the environment that determines these upper limits. Certainly it is not a shortage of niches, for when we consider the niches occupied by alpine Orthoptera we find that none of these Orthoptera is very specialized. There are, for example, three resident species on the tundra at Station 5a. *Melanoplus dodgei and *Aeropedellus clavatus are herbivorous, the former favoring forbs and the latter grasses and sedges but neither highly restricted in food. Ana-brus simplex is even less specialized, being more of an opportunistic omnivore. One can draw an obvious analogy between these niches and human occupations (see Odum et al., 1960) if we consider the alpine community not an urban but a pioneer, rural community. Melanoplus and Aeroped'ellus correspond to farmers, the former concentrating on vegetables, the latter on grains; Anabrus is, of course, even more of a "pioneer," practicing mixed agriculture combined with hunt- ing. (Analyzing the niches at Station la, where as many as nine species of one genus, Melanoplus, have been taken in one collection, is a much more complex process. Perhaps we need to recall the specialists in a medical center, an urban development, to provide us with an adequate analogy!)

Even in our earliest collecting we were im- pressed by our observation that the small number of species at high altitudes seemed to "make up" for these small numbers by large numbers of individuals. This tendency for an inverse relation between species diversity and population size, however, does not occur all along the gradient. The mean population size per species does not differ greatly among the populations below timber line (Table 8), but with increasing altitude above timber line (Stations 4d to 5c) the species re- maining in the fauna show a remarkably high productivity. It is as if some checks had been removed, for the same species do occur at lower altitudes in smaller populations.

Though these numbers are relatively large, they never reach, in our experience, the density characteristic of some species on the plains. What limits the numbers, even at these high densities? One limiting factor is the relatively low biotic potential of tundra species; they do not produce as many eggs as do the common pest species, and this prevents a big increase in a single season. It is unlikely that food is a limiting factor for the

herbivores (Hairston et al., 1960) ; certainly we have seen no evidence of damage to the tundra due to insects. The suggestion by Hairston et al. that predators may be significant in regulating her- bivore populations deserves particular considera- tion. Mani (1962) has pointed to the rather large proportion of predators at high altitudes as a characteristic of the fauna, though he was considering somewhat higher altitudes-even com- parativiely-than ours, altitudes corresponding with those of or near the Aeolian Zone of Swan (1968 and earlier papers). Certainly the numerous spiders and carabid beetles (Schmoller, 1968), as well as birds and small mammals, can be significant predators on Orthoptera, especially young stages. We are unwilling, however, to discount weather and climate as major factors in the control of high altitude population size, perhaps because, in the extreme environment of which we are writing, their effects can appear so potentially disastrous.

ACKNOWLEDGMENTS

The major field studies during 1958-1962, inclusive, were made possible by Grant G-5007 from the National Science Foundation, here gratefully acknowledged. The authors are indebted to the following for assistance in field studies during the summers of 1958, 1959, and 1960: Donald H. Van Horn, all three seasons; Ann (Stalheim) Smith, 1959 and 1960; Douglas G. Alexander, Kathleen (Davis) Alexander, and Carlos Mar- quez, 19,58; Sunthorn Suanraksa (now Sirivana- korn), 1959; Donald Blumberg, 1960. Douglas and Kathleen Alexander also made observations on overwintering juveniles during the winter and spring 1957-1958.

The senior author wishes to express apprecia- tion for a grant-in-aid in 1949 from the Council on Research and Creative Work, University of Colorado, and for a Faculty Fellowship during the spring semester, 1960, from the Council. Philip A. Buscemi was of special assistance in 1949 and 1950.

The authors are indebted to Donald H. Van Horn for all photographs of field stations, and to Ashley Gurney, U.S. National Museum, for advice on taxonomic matters. Other assistance is acknowledged in the text.

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altitudinal and seasonal distribution of orthoptera in the rocky mountains of northern colorado

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