environmental variability and biogeography: the relationship between bathymetric distribution and...

RESEARCH PAPER

© 2003 Blackwell Publishing Ltd. http://www.blackwellpublishing.com/journals/geb

Global Ecology & Biogeography

(2003)

12

, 499–506

Blackwell Publishing Ltd.

Environmental variability and biogeography: the relationship between bathymetric distribution and geographical range size in marine algae and gastropods

CHRISTOPHER D. G. HARLEY*, KATHERINE F. SMITH† and VICKI L. MOORE*

,

‡

*

Hopkins Marine Station, Oceanview Blvd., Pacific Grove, CA 93950, U.S.A.;

†

Department of Ecology, Evolution, and Marine Biology, University of California, Santa Barbara CA 93106, U.S.A.;

‡

Department of Biology, San Francisco State University, San Francisco CA 94132,

U.S.A. E-mail: [email protected]

ABSTRACT

Aims

Gradients of environmental variability have been pro-posed to explain spatial variation in patterns of geographicalrange size. We explore this relationship in NE Pacific algaeand NW Atlantic gastropods by using the characteristics ofspecies’ bathymetric distributions as a proxy for tolerance ofenvironmental variability.

Location

NE Pacific and NW Atlantic.

Methods

Data on species bathymetric and geographicaldistributions were compiled from the literature.

Results

For both algae and gastropods, species that inhabithighly seasonal, shallow depth zones have broader latitudinalranges, and occupy more biogeographical provinces, thanspecies that live in more temporally stable, deeper zones.

Furthermore, species that tolerate spatial variability along thebathymetric axis, i.e. those that occur in multiple depth zones,have broader geographical ranges than species restricted tofewer depth zones.

Main conclusions

Within-range environmental variability,through both space and time, is predictive of large geograph-ical ranges for marine algae and gastropods. Analysis ofspecies distributions across perpendicular gradients (e.g. depthand latitude) is a powerful approach to discerning the mech-anisms that govern biogeographical patterns, and provideseasily obtainable broad-brush predictions regarding thebiogeographical outcomes of global change.

Key words

Atlantic Ocean, benthic macroalgae, depthgradients, environmental variability, gastropods, latitude,marine biogeography, Pacific Ocean, seasonality, species ranges.

INTRODUCTION

Biogeographers have long noted that aggregate patterns ofspecies range sizes are spatially and temporally variable(Janzen, 1967; Jackson, 1974; Jablonski & Valentine, 1981,1990; Koch & Morgan, 1988; Ricklefs & Latham, 1992;Levin

et al

., 2001). Stevens (1989, 1992, 1996) proposed thatecographic trends in species range size are driven by environ-mental variability; species that exist in seasonal (temporallyvariable) environments must tolerate a wide range of environ-mental conditions, and are thus well suited to inhabit a broadgeographical range. Explicit tests of this hypothesis have

proven difficult because trends in environmental variabilitycovary with a suite of additional factors across most spatialgradients. This limitation can be surmounted, however, bythe use of gradients of environmental variability that runperpendicular to the spatial axis of interest. For example,Jackson (1974) and Jablonski & Valentine (1981) exploredthe determinants of geographical range size in marinemolluscs by comparing shallow and deep-water taxa. Shallowmarine environments experience more variability thandeeper environments across a range of temporal scales (Box1). Accordingly, molluscs that were able to live in highly sea-sonal shallow (0–1 m depth) habitats tended to have broadergeographical ranges than species restricted to deeper waters,suggesting that tolerance of seasonality confers a tolerance ofgeographical-scale environmental variation as well (Jackson,1974; Jablonski & Valentine, 1981).

Correspondence: Christopher D. G. Harley, Hopkins MarineStation, Oceanview Blvd., Pacific Grove, CA 93950, U.S.A. E-mail:[email protected]

http://www.blackwellpublishing.com

500

C. D. G. Harley, K. F. Smith and V. L. Moore

© 2003 Blackwell Publishing Ltd,


,

12

, 499–506

In this paper, we extend these earlier analyses of depth vs.latitudinal range to benthic macroalgae from the NE Pacificand gastropods from the NW Atlantic. We examine the roleof seasonal environmental variation by comparing latitudinalrange sizes for species that occupy shallow vs. deeper depthzones. In addition to temporal variation, we investigate theimportance of depth-related

spatial

variation by comparingspecies that occupy different numbers of distinct depth zones.We thus explore the prediction that species whose bathymetricdistributions encompass greater spatial or temporal variabilitywill exhibit broad latitudinal ranges.

METHODS

Algal distributional data were compiled from the literature(Scagel, 1966, 1967; Abbot & Hollenberg, 1976; Scagel

et al

.,1986, 1989; O’Clair & Lindstrom, 2000). Algal species (

n

=460) included in our dataset occur at least in part betweenPoint Conception, California, and the Gulf of Alaska, livedirectly on rocky substrata, thus excluding obligate epiphytes,endophytes, and species that live on sand, and have knownbathymetric and latitudinal distributions. Distributional infor-mation for West Atlantic gastropods, based on live captures

Box 1 Temporal variability and depth

Box 1. Our interpretation of the macroecological patterns we describe hinges on the assumption that environmental varia-bility decreases with depth. Such a decline in variability has been documented for a suite of environmental variables, includ-ing temperature, salinity, and nutrients (Barnett & Jahn, 1987; Pickard & Emery, 1990). Temperature in particular is acrucial abiotic variable because it has demonstrable effects on the physiology and fitness of marine organisms (reviewed inTomanek & Helmuth, 2002), and because it is related to both latitudinal and bathymetric ranges of benthic marine species(e.g. Newell, 1979; Hoek, 1982). To illustrate thermal variability with depth, we present temperature data for the period ofOctober 2000 through October 2001 from a mooring in Monterey Bay, CA, USA (data courtesy of the Monterey BayAquarium Research Institute), and from a nearby intertidal site at the Hopkins Marine Station in Pacific Grove, CA (datacourtesy of B. Helmuth, see Helmuth et al., 2002 for details).

Not surprisingly, thermal variability is greatest in the intertidal zone (open symbols), where daily exposure to terrestrialconditions results in annual thermal maxima and minima that are well beyond the range of seawater temperature (leftpanel). The annual range in seawater temperature is modest above 50 m depth, and declines steadily towards 250 m.Because many organisms are adapted to seasonally fluctuating environments, we further explored the data by comparingthe maximum annual temperature range with the maximum range found over the course of a single day and over the courseof a fortnight (which corresponds to a single spring-neap tidal cycle). At all three time scales (right panel), variability wasextreme in the intertidal zone, intermediate between 1 m and 50 m, and very low at depths > 50 m. These three bathymetricthermal regimes further support the bathymetric zones we selected for analysis.

Depth distribution and latitudinal range of algae and gastropods

501



,

12

, 499–506

or observations, was compiled from the Western AtlanticGastropod Database (with the permission of the Academy ofNatural Sciences, Philadelphia, USA). In our analyses, weincluded species (

n

= 1096) that occur at least in part in thenorthern hemisphere (0

°

N

−

82

°

N), and whose bathymetricrange is restricted to the continental shelf (< 200 m depth).Species that occur in deeper waters are less well sampled andoften exhibit inconsistent biogeographical patterns (i.e. Rex,1981; Etter & Grassle, 1992), and are thus beyond the scopeof this paper.

Latitudinal range endpoints were determined to the nearestdegree for algae and to 0.01-degree for gastropods whenpossible. Bathymetric range limits were recorded to thenearest metre. For intertidal algae, the low, mid, and highintertidal zones (see below) were each assumed to span onevertical metre. For both taxa, we assumed that speciesoccurred at all depths and latitudes between reported rangeendpoints.

In addition to latitudinal range, we recorded the number ofbiogeographical provinces occupied by each species. Provin-cial boundaries were defined by locating latitudinal bandswhere the number of algal or gastropod species range end-points exceeded the grand mean by more than two standarddeviations. In the Pacific, we recognized the following sixprovinces: Central American (12

°

S–24

°

N), Californian (25

°

–34

°

N), Montereyan (34.5

°

–36.5

°

N), Oregonian (37

°

–48

°

N),Alaskan (50

°

–61

°

N), and Arctic (62

°

–70

°

N). In the Atlantic,the following six provincial divisions were used: South Amer-ican (55

°

–24

°

S), Brazilian (23

°

S–9

°

N), Caribbean (12

°

–25

°

N),Carolinian (28

°

–32

°

N), Virginian (35

°

–41

°

N), and NorthAtlantic (42

°

–80

°

N). Although the break at Cape Cod (41

°

–42

°

N in the Atlantic) does not contain as many range end-points as the other provincial boundaries, we have included itbecause the number of range endpoints is large relative to thetotal number of gastropod species at that latitude. Overall,the biogeographical provinces as outlined above coincidewith previously published boundaries (see Briggs, 1995). Smallgaps between provinces (e.g. 25

°

–28

°

N in Florida) corre-spond to diffuse boundaries (i.e. many southern and northernrange limits were spread relatively evenly between 25

°

–28

°

N).For a species to be included in two neighbouring provinces, itmust completely span any such gap and occur in at least afraction of both provinces. Species whose distributions werecontained entirely within a gap were treated as occupying asingle province.

Species were binned into environmentally relevant depthzones. For algae these were high intertidal, mid intertidal, lowintertidal, and subtidal, categorizations that are consistentlyapplied in the phycological literature. Although many gastro-pods are also restricted to the intertidal, our data lacked thebathymetric resolution to provide insight into fine-scale inter-tidal distributions. Therefore, we binned gastropods into thefollowing three depth zones: the intertidal zone from 0 to

1 m, the inner sublittoral zone from 1 to 50 m, and the outersublittoral zone from 50 to 200 m. The inner sublittoral is thepermanently submerged zone with sufficient light to supportphotosynthesis, while the outer sublittoral is a dimly lit zonethat extends to the approximate depth of the continentalshelf break (Webber & Thurman, 1991). These zones corre-spond well with bathymetric patterns of temporal variability(see Box 1), and are typified by distinct biogenic habitattypes and communities of species (Webber & Thurman,1991).

We address two components of environmental variability:spatial variability and temporal variability. In the former case,we conducted analyses on species’ geographical range size(in latitudinal degrees or as the number of biogeographicalprovinces occupied) vs. the ordinal number of depth zones occu-pied. Because position along the bathymetric gradient hasbeen correlated with species’ total bathymetric range in metres(Pineda, 1993; Stevens, 1996; Smith & Brown, 2002), we ranan analysis of covariance (

ancova

) on geographical range andthe number of depth zones occupied with bathymetric range(in metres) as a covariate. Only four algal species occupied allfour depth zones; therefore, we combined the 3- and 4-zonecategories into a single 3 + zone category. To address tempo-ral variability, we compared the latitudinal ranges of speciesliving in highly seasonal, shallow depth zones to those of spe-cies occupying comparatively temporally uniform deep-waterzones. For these analyses, we defined ‘shallow’ species as thosethat occupied more shallow zones than deep zones and ‘deep’species as those that occupied more deep zones than shallowzones. For example, algae restricted to the high or mid inter-tidal were defined as shallow, as were those that ranged fromthe high to mid or high to low intertidal. ‘Shallow’ gastropodswere those restricted to the intertidal zone, and those thatspanned the intertidal and inner sublittoral zones. Speciesthat occupied an intermediate bathymetric position (algaethat spanned mid and low zones, and gastropods restricted tothe inner sublittoral zone) and species that spanned all possi-ble depth zones were excluded from this analysis. Because thenumber of depth zones occupied may confound interpreta-tion of the latitudinal ranges of shallow vs. deep species, datafor these analyses were blocked by the number of depth zonesoccupied. To improve the normality of the data, latitudinalranges of gastropods and bathymetric ranges of both taxawere ln(

x

) transformed for statistical analysis. Analyses wereconducted in JMP version 3.2.6 (SAS Institute).

RESULTS

The total number of bathymetric zones occupied was a strongpredictor of geographical range size for both taxa. Algae andgastropods that inhabited multiple depth zones had broaderlatitudinal ranges (Fig. 1a, Table 1a), and occupied morebiogeographical provinces (Fig. 1b, Table 1b), than those that

502




,

12

, 499–506

were restricted to fewer depth zones. The covariate, absolutebathymetric range in metres, did not have a significant effecton geographical range size for these taxa (Table 1), indicatingthat the relationships between depth distribution and geo-graphical range for algae and gastropods were driven bythe occupancy of multiple, environmentally distinct depthzones, rather than by absolute bathymetric range in and ofitself.

When the latitudinal range data were broken down into allpossible bathymetric zone occupancy combinations, anotherpattern emerged. For both taxa, species inhabiting shallowerdepths had broader latitudinal ranges than those living atdeeper depths (Fig. 2a). By inspection, this qualitative patternholds for all five possible comparisons (1-zone, 2-zone,and 3-zone occupancy categories for algae, and 1-zone and2-zone occupancy categories for gastropods). The tendency forshallow species to have broader latitudinal ranges than deepspecies was highly significant for both taxa, as was the block-ing factor of number of zones occupied (Table 2a). Shallow-dwelling species in both taxa also occurred in significantlymore biogeographical provinces than deep-dwelling species(Fig. 2b, Table 2b). As with the latitudinal range analysis,the blocking factor (number of zones occupied) was alsosignificant.

DISCUSSION

Environmental variability and species distributions

Environmental variability, particularly in the form of season-ality, has been proposed as a prominent driving force behindgeographical patterns of species range size (Stevens, 1989,1992, 1996). Here we address two predictions that stem fromthis proposed relationship. First, species that occupy seasonalhabitats are expected to have broader geographical rangesthan those that occur in nonseasonal habitats. Second, speciesthat occur across a range of local environmental variation in

Fig. 1 (a) Latitudinal range and (b) number of biogeographicalprovinces occupied as functions of the number of bathymetric zonesoccupied for benthic algae and gastropods. Back-transformed dataare shown for gastropods. Error bars are standard error. Statistics arepresented in Table 1.

Table 1 Results of analyses of covariance. Algae and gastropods exhibita positive correlation between the number of depth zones occupiedand (a) latitudinal range and (b) the number of biogeographicalprovinces occupied. The covariate, actual depth range in metres(ln(x) transformed), is not related to geographical range size. P-valuesthat are significant after sequential Bonferroni correction of α areindicated in bold(a) Latitudinal range size (degrees)

(b) Number of biogeographical provinces occupied

Taxon variable F P r 2

Algae No. of zones occupied 19.2 << 0.001 0.106Depth range (m) 0.04 0.835 0.106

Gastropods No. of zones occupied 55.4 << 0.001 0.116Depth range (m) 1.54 0.215 0.116

Taxon variable F P r 2

Algae No. of zones occupied 13.3 << 0.001 0.087Depth range (m) 1.47 0.226 0.087

Gastropods No. of zones occupied 50.7 << 0.001 0.123Depth range (m) 0.20 0.659 0.123

Table 2 Results of analysis of variance. The influence of bathymetricdistribution (shallow vs. deep) on (a) latitudinal range and (b) thenumber of biogeographical provinces occupied was apparent forboth algae and gastropods. The blocking factor, ordinal number ofzones occupied, was also significantly related to range size in all cases.P-values that are significant after sequential Bonferroni correctionof α are indicated in bold(a) Latitudinal range size (degrees)

(b) Number of biogeographical provinces occupied

Taxon Variable F P r 2

Algae Depth (shallow vs. deep) 9.55 0.002 0.110No. of zones occupied 24.6 << 0.001 0.110

Gastropods Depth (shallow vs. deep) 9.13 0.003 0.046No. of zones occupied 30.9 << 0.001 0.046

Taxon Variable F P r 2

Algae˙ Depth (shallow vs. deep) 7.90 0.005 0.095No. of zones occupied 20.9 << 0.001 0.095

Gastropods Depth (shallow vs. deep) 4.40 0.036 0.028No. of zones occupied 19.6 << 0.001 0.028


503



,

12

, 499–506

Fig. 2 (a) Latitudinal range and (b) number of biogeographical provinces occupied as functions of bathymetric distribution. Data are brokendown into all possible bathymetric zone occupancy combinations. For algae, zones are high intertidal, mid intertidal, low intertidal, and subtidal.For gastropods, zones are intertidal (0–1 m), inner sublittoral (1–50 m), and outer sublittoral (50–200 m). Sample sizes are indicated inparentheses. Back-transformed data are shown for gastropod latitudinal ranges. Error bars are standard error. Statistics are presented in Table 2.

504




,

12

, 499–506

space (e.g. multiple habitat types) are similarly expected tohave broader geographical ranges than species restricted tospecific habitats at the local scale.

These predictions have been difficult to test. Gradients inseasonality are typically accompanied by covariates such asspecies diversity, making it difficult to differentiate betweenthe mechanisms that drive patterns of geographical range sizeand those that do not. Even more problematic is the role ofenvironmental variation in space; investigations of spatialvariability encounter problems of nonindependence whenone considers broad occupancy patterns at one spatial scaleto be a predictor of extensive ranges at larger scales (see,e.g. Jablonski & Valentine, 1990). Here, we circumvent theseproblems by incorporating environmental variability alonga spatial axis (bathymetry) that is independent of the latitu-dinal component of geographical range. Prior studies haveused this approach to demonstrate that fossil and extantmolluscs from seasonal shallow-water environments have largergeographical ranges than deeper-dwelling species (Jackson,1974; Jablonski, 1980; Jablonski & Valentine, 1981). Ourresults confirm these earlier findings; NE Pacific algae in thehighly variable high and mid intertidal zones, and NW Atlanticgastropods in the relatively seasonal shallow-water zone, hadbroader latitudinal ranges than more deeply dwelling species.

The second prediction of the environmental variabilityhypothesis, that of variability in space, has received littleattention. However, much as previous workers have usedbathymetric position as a proxy for seasonality, we were ableto use bathymetric range as a proxy for spatial variation inenvironmental conditions. A positive relationship betweenbathymetric range and geographical range was proposed bySanders & Goulden, (1977), who noted that deep-sea benthicinvertebrate taxa with broad depth ranges had larger zoo-geographical ranges than taxa with narrower depth ranges.NE Pacific algae and NW Atlantic gastropods support theexpectation that spatial variation along the bathymetricaxis is also predictive of geographical range size; species thatoccurred in more depth zones occupied more biogeographicalprovinces and had larger latitudinal ranges. However, wefound that absolute bathymetric range (in metres) was not agood predictor of geographical range. This is not surprising;bathymetric range is a poor surrogate for environmentalvariation across the continental shelf because gradients inphysical variables and changes in species composition aredisproportionately steep in intertidal and shallow waterhabitats. Our results indicate that the number of environmentallyrelevant depth zones occupied by a species was far moreuseful in predicting latitudinal range size than was absolutebathymetric range.

Conversely, a division of latitude into segments (e.g. bioge-ographical provinces) does not measurably improve ourunderstanding of the biogeographical patterns we analysed. Ifanything, the use of the number of biogeographical provinces

occupied in place of latitudinal range slightly decreases thevariance explained in our statistical models (see the

r

2

valuesin Tables 1 and 2). In contrast to environmentally relevantbathymetric zones, which get markedly broader with depth,the size of homogenous regions of latitude (coastal biogeo-graphical provinces) do not change monotonically with lati-tude (see Briggs, 1995). Furthermore, while the widths of thesmallest and largest depth zones defined here vary by a factorof 150, the latitudinal extent of the largest and smallest bio-geographical provinces differ by a single order of magnitude.Therefore, a division of the latitudinal continuum into dis-crete provinces should not be expected to provide the sameanalytical improvement as the division of the bathymetricaxis into depth zones.

It is worth noting that the nonparallel gradient approachtaken here is not immune to alternative interpretations.Certainly, seasonality is not the only factor that varies alongthe depth gradient. Benthic species richness also varies withdepth across the continental shelf (see, e.g. Jackson, 1974),and regions of high species richness have been correlatedwith reduced geographical range size in terrestrial systems,purportedly due to competitive effects (Stevens, 1989, 1992).Although a thorough analysis of species diversity patterns isbeyond the scope of this report, we do not believe that speciesrichness or competition play large roles in influencing the lat-itudinal range sizes of algae or gastropods. Gastropod speciesrichness peaks at the surface in the tropics, and at shallow tointermediate depths in the temperate zone (unpublished data).Despite reduced species richness along the continental shelfmargin, species restricted to those deep-water habitats havesignificantly smaller geographical ranges than their counter-parts in more species rich shallow-water environments. Algalspecies richness also drops off in deeper habitats without aconcomitant increase in latitudinal range. Furthermore, althoughalgal competitive ability is linked to morphological functionalgroup (Steneck & Dethier, 1994), there is no relationshipbetween algal functional group and latitudinal range size inthe NE Pacific (Harley & Moore, unpublished data). Theapparent lack of a competition effect was also noted by Jack-son (1974), who concluded that ‘competition does not appearto be a major factor limiting geographical distributions oftropical infaunal bivalves’. The pattern of decreasing latitudi-nal range size with increasing depth of occurrence may alsobe influenced by sampling error. The range of rare speciescould be underestimated because they did not appear in oneor more samples at the edges — either upper, lower, northern,or southern — of their range. Such incomplete sampling indeep waters may account for the apparent decline in latitudi-nal range extent with increasing depth of occurrence. It alsomeans that the maximum depths of occurrence for somespecies are underestimated, so that depth ranges in the deepwater of the continental shelf may be somewhat greater thanour analyses suggest. We have several reasons to believe that


505



,

12

, 499–506

such limitations of sampling did not alter the general relation-ships between bathymetric and geographical distributionsthat we describe. First, algal sampling effort should have beenrelatively uniform across the three intertidal zones, and theremoval of strictly subtidal algae from our analyses doesnot affect our results. Second, the sampling bias should bemost pronounced for rare species. When the analyses areconducted only on those algae described in the literature ascommon or abundant, we obtain the same results (Harley &Moore, unpublished data). Finally, all the range differenceswe document are significant when we analyse the number ofbiogeographical provinces occupied. At the coarse scale ofbiogeographical provinces, it is unlikely that sampling biashas a strong influence on the patterns of interest.

Implications

Our results allow us to make several predictions regardingfuture environmental and biological change in marineecosystems. Several studies (Jackson, 1974; Jablonski, 1980;Jablonski & Valentine, 1981) have reported that shallowoccurring species have greater temporal (geological) rangesthan deeper-dwelling species, implying that the relationshipbetween environmental variability and species range sizeoperates across large spatial and large temporal scales. Vul-nerability to environmental change may differentially affectdeeper-dwelling species over much shorter time scales as well.If our predictions are correct, species inhabiting environ-mentally stable, deep-water zones will be more susceptible tocertain types of global environmental change (e.g. increasingwater temperatures) than the more eurytopic, shallow waterspecies. In an analysis of invertebrate species abundance shiftsassociated with warming sea surface temperatures betweenthe early 1930s and the mid 1990s, Sagarin

et al

. (1999) foundthat whereas only 3 of 14 high intertidal species had under-gone significant changes in abundance, the abundances of29 of 44 low intertidal species had changed. Further exa-mination of their published data revealed that the differencein susceptibility to climate-related change between zones ishighly significant (

χ

2

test: likelihood ratio = 8.77,

P

= 0.003).Bathymetric distributional information may also allow us

to predict the likelihood of success of biological invasions.The link between habitat generalism and invasion successbears both theoretical and empirical support (see, e.g. Lodge,1993; Ruesink

et al

., 1995; references therein). It seemsprobable that, once they have been transported beyondtheir native range, bathymetric generalists will be morelikely to become established than bathymetric specialists. Allelse being equal, we predict that shallow-water speciesshould be more likely to establish successfully in new geo-graphical regions than deep-water species. These hypothesesawait the compilation of the necessary data to allow forrigorous tests.

The analysis of species distributions across perpendicularphysical gradients holds enormous promise for clarifying therelationships between the physical and biological environmentand biogeographical phenomena ranging from patterns ofrange size (this study) to species diversity gradients (Körner,2000). Each of the patterns and implications we havepresented call for further research and development of thisapproach, not only for marine organisms, but also for terres-trial taxa, such as those distributed across gradients of lati-tude and elevation. By extending analyses to multiple systemsand taxonomic groups, we will come closer to understandingthe general role of environmental variability on speciesgeographical distributions.

ACKNOWLEDGMENTS

We thank Steve Gaines, Brian Kinlan, Dov Sax, Terry Tate,T.P. Train, and two anonymous reviewers for thoughtful dis-cussion and criticism of this manuscript. Brian Helmuth andthe Monterey Bay Aquarium Research Institute generouslyshared their temperature data. Funding was provided by anAchievement Rewards for College Scientists Foundation fel-lowship (to CH), National Science Foundation GraduateResearch Fellowships (to CH and KS), and the Partnershipfor Interdisciplinary Studies of Coastal Oceans. This is PISCOcontribution no. 120.

REFERENCES

Abbott, I.A. & Hollenberg, G.J. (1976)

Marine algae of California

.Stanford University Press, Stanford, CA.

Barnett, A.M. & Jahn, A.E. (1987) Pattern and persistence of a near-shore planktonic ecosystem off southern California.

ContinentalShelf Research

,

7

, 1–25.Briggs, J.C. (1995)

Global biogeography

. Elsevier, Amsterdam.Etter, R.J. & Grassle, J.F. (1992) Patterns of species diversity in the

deep sea as a function of sediment particle size diversity.

Nature

,

360

, 576–578.Helmuth, B., Harley, C.D.G., Halpin, P.M., O’Donnell, M.,

Hofmann, G.E. & Blanchette, C.A. (2002) Climate change andlatitudinal patterns of intertidal thermal stress.

Science

,

298

,1015–1017.

van den Hoek, C. (1982) The distribution of benthic marine algae inrelation to the temperature regulation of their life histories.

Biolog-ical Journal of the Linnean Society

,

18

, 81–144.Jablonski, D. (1980) Apparent versus real biotic effects of transgressions

and regressions.

Paleobiology

,

6

, 397–407.Jablonski, D. & Valentine, J.W. (1981) Onshore-offshore gradients in

recent eastern Pacific shelf faunas and their paleobiogeographicsignificance.

Evolution Today, Proceedings of the Second Inter-national Congress of Systematic and Evolutionary Biology

(ed. byG.C.E. Scudder and J.L. Reveal), pp. 441–453. Carnegie-MellonUniversity, Pittsburgh, Pennsylvania.

Jablonski, D. & Valentine, J.W. (1990) From regional to total geographicranges: testing the relationship in recent bivalves.

Paleobiology, 16,126–142.

506 C. D. G. Harley, K. F. Smith and V. L. Moore

© 2003 Blackwell Publishing Ltd, Global Ecology & Biogeography, 12, 499–506

Jackson, J.B.C. (1974) Biogeographic consequences of eurytopy andstenotopy among marine bivalves and their evolutionary significance.American Naturalist, 108, 541–560.

Janzen, D.H. (1967) Why mountain passes are higher in the tropics.American Naturalist, 100, 233–249.

Koch, C.F. & Morgan, J.P. (1988) On the expected distribution ofspecies’ ranges. Paleobiology, 14, 126–138.

Körner, C. (2000) Why are there global gradients in species richness?Mountains might hold the answer. Trends in Ecology and Evolution,15, 513–514.

Levin, L.A., Etter, R.J., Rex, M.A., Gooday, A.J., Smith, C.R.,Pineda, J., Stuart, C.T., Hessler, R.R. & Pawson, D. (2001) Envi-ronmental influences on regional deep-sea species diversity. AnnualReview of Ecology and Systematics, 32, 51–93.

Lodge, D.M. (1993) Species invasions and deletions. Biotic Interac-tions and Global Change (ed. by P.M. Kareiva, J.G. Kingsolver andR.B. Hvey), pp. 367–387. Sinaver, Sunderland, Mass.

Newell, R.C. (1979) Biology of intertidal animals. Marine EcologicalSurveys Ltd, Kent.

O’Clair, R.M. & Lindstrom, S.C. (2000) North Pacific seaweeds.Plant Press, Auke bay, AK.

Pickard, G. & Emery, W. (1990) Descriptive physical oceanography,5th edn. Pergamon, Oxford.

Pineda, J. (1993) Boundary effects on the vertical ranges of deep-seabenthic species. Deep-Sea Research, 40, 2179–2192.

Rex, M.A. (1981) Community structure in the deep-sea benthos.Annual Review of Ecology and Systematics, 12, 331–353.

Ricklefs, R.E. & Latham, R.E. (1992) Intercontinental correlation ofgeographical ranges suggests stasis in ecological traits of relictgenera of temperate perennial herbs. American Naturalist, 139,1305–1321.

Ruesink, J.L., Parker, I.M., Groom, M.J. & Kareiva, P.M. (1995)Reducing the risks of nonindigenous species introductions.Bioscience, 45, 465–477.

Sagarin, R.D., Barry, J.P., Gilman, S.E. & Baxter, C.H. (1999)Climate-related change in an intertidal community over short andlong time scales. Ecological Monographs, 69, 465–490.

Sanders, H.L. (1977) Evolutionary ecology and the deep-seabenthos. Changing scenes in natural sciences 1776–1976 (ed.by C.E. Goulden), pp. 223–243. Academy of Natural Sciences,Philadelphia, Pennsylvania.

Scagel, R.F. (1966) Marine algae of British Columbia and northernWashington, Part I: Cholophyceae (green algae). National Museumof Canada. Bulletin no. 207, Ottawa.

Scagel, R.F. (1967) Guide to common seaweeds of British Columbia.A. Sutton, British Columbia.

Scagel, R.F., Gabrielson, P.W., Garbary, D.J., Golden, L., Hawkes, M.W.,Lindstrom, S.C., Oliveira, J.C. & Widdowson, T.B. (1989) Asynopsis of the benthic marine algae of British Columbia, southeast

Alaska, Washington and Oregon, Phycological Contribution, 3, 1–532.

Scagel, R.F., Garbary, D.J., Golden, L. & Hawkes, M.W. (1986) Asynopsis of the benthic marine algae of British Columbia,northern Washington and southeast Alaska. University of BritishColumbia, Vancouver, B.C.

Smith, K.F. & Brown, J.H. (2002) Patterns of diversity, depth rangeand body size among pelagic fishes along a gradient of depth.Global Ecology and Biogeography, 11, 313–322.

Steneck, R.S. & Dethier, M.N. (1994) A functional group approachto the structure of algal-dominated communities. Oikos, 69, 476–498.

Stevens, G.C. (1989) The latitudinal gradient in geographical range:how so many species coexist in the tropics. American Naturalist,133, 240–256.

Stevens, G.C. (1992) The elevational gradient in altitudinal range: anextension of Rapoport’s latitudinal rule to altitude. AmericanNaturalist, 140, 893–911.

Stevens, G.C. (1996) Extending Rapoport’s rule to marine fishes.Journal of Biogeography, 23, 149–154.

Tomanek, L. & Helmuth, B. (2002) Physiological ecology of rockyintertidal organisms: a synergy of concepts. Integrative andComparative Biology, 42, 771–775.

Webber, H.H. & Thurman, H.V. (1991) Marine biology. HarperCollins, New York.

BIOSKETCHES

C.D.G. Harley is a postdoctoral researcher at Stanford University’s Hopkins Marine Station. His research interests centre on the influence of the abiotic environment on species distributions and interspecific interactions in marine ecosystems. He enjoys long walks on the beach.

K.F. Smith is a Ph.D. student in the Department of Ecology, Evolution, and Marine Biology at The University of California, Santa Barbara. Her research focus is on biogeography and macroecology, with specific interest in the mechanisms that influence global patterns of emerging infectious disease in terrestrial and marine environments.

V.L. Moore is a masters student at San Francisco State University. While currently studying phylogenetic relationships among Bay Area damselflies, her interests include insect ecology and systematics, limnology, and aquatic entomology, especially in temporally fluctuating environments.

environmental variability and biogeography: the relationship between bathymetric distribution and...

Documents