marine biotic interchange between the northern and southern hemispheres

Paleontological Society

Marine Biotic Interchange Between the Northern and Southern HemispheresAuthor(s): David R. LindbergReviewed work(s):Source: Paleobiology, Vol. 17, No. 3 (Summer, 1991), pp. 308-324Published by: Paleontological SocietyStable URL: http://www.jstor.org/stable/2400871 .Accessed: 18/10/2012 16:54

Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at .http://www.jstor.org/page/info/about/policies/terms.jsp

.JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range ofcontent in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new formsof scholarship. For more information about JSTOR, please contact [email protected].

.

Paleontological Society is collaborating with JSTOR to digitize, preserve and extend access to Paleobiology.

http://www.jstor.org

http://www.jstor.org/action/showPublisher?publisherCode=paleo

http://www.jstor.org/stable/2400871?origin=JSTOR-pdf

http://www.jstor.org/page/info/about/policies/terms.jsp

Paleobiology, 17(3), 1991, pp. 308-324

Marine biotic interchange between the northern and southern hemispheres

David R. Lindberg

Abstract.-Patterns of bipolar or antitropical distributions occur in a diverse array of marine invertebrate, vertebrate, and plant groups in the eastern Pacific Ocean. Available geologic and paleontological evidence does not support vicariance as a process in the creation of these distributions but instead favors biotic interchange between hemispheres. Moreover, the timing of these events suggests several breaches (both northward and southward) of the tropics rather than a single event. The fossil record is extremely important in delimiting potential hypotheses and allowing correlation with vicariance events. The congruence of some interchanges with major regional tectonic activity and others with Pleistocene glaciations is not surprising and argues for a plurality of mechanisms. Extinction of endemic taxa following interchange among marine invertebrates is rare, and none of the antitropical distributions reviewed here suggests that the arrival of a taxon in the adjoining hemisphere resulted in the extinction of an endemic taxon. Instead, interchange and endemic taxa coexist. In contrast to the extinction patterns, the patterns of radiations are extremely diverse with some immigrant taxa undergoing remarkable radiations, whereas other taxa are represented by single species. Temperate nearshore rocky communities in both the northern and southern hemispheres appear to be mosaics of species that share common ancestry (because of interchange), are cosmopolitan, and have independent origins within the region. Although some communities appear to be organized around products of interchange (e.g., kelp forests of California and Chile), only the taxa have immigrated; linkages and interactions between species are independent and locally derived.

David R. Lindberg. Museum of Paleontology, University of California, Berkeley, California 94720

Accepted: April 10, 1991

Introduction Discontinuous distributions of marine taxa

have long been recognized in many nearshore regions of the modern ocean (Darwin 1859; Berg 1933; Ekman 1953). They have been produced by both vicariance and dispersal events (e.g., the division of the tropical New World nearshore fauna into Panamic and Ca- ribbean components by movement of the Ca- ribbean plate through the gap between North and South America and subsequent local uplift [Vermeij 1978], and the Neogene migration of larvae and adult North Pacific invertebrates through the Bering Strait into the Arctic Ocean, and ultimately, the North At- lantic Ocean [Durham and MacNeil 1967; Vermeij 1978,1991]). Many of the best-known and well-documented cases of discontinuous distributions of marine taxa involve east-west interchanges or separations (Ekman 1953; Vermeij 1978). Because many of these interchanges and separations are longitudinal in direction, water temperature seldom serves as a barrier against interchange. For example,

the interchange between the North Pacific and North Atlantic was between two temperate faunas that had been previously separated from one another by Beringia (during the Pleistocene and Holocene this avenue has been regulated by glacial and interglacial cycles), and the closure of the Panamic portal by tectonic events separated two tropical faunas. Although the interchange between the Red Sea and Mediterranean was in a north- south direction via the Suez Canal (Por 1971; Vermeij 1978), it occurred entirely within the tropics.

In contrast to these patterns are those sug- gesting interchange between regions in the northern and southern hemispheres, interchanges that produce antitropical or bipolar distributional patterns. Ekman (1953: p. 250) defined bipolarity as "a distribution spread over a region in the northern and one in the southern hemisphere with a gap in distribution between the two." Hubbs (1952) pointed out that very few of the taxa showing this distributional pattern were actually re-

? 1991 The Paleontological Society. All rights reserved. 0094-8373/91/1703-0008/$1.00

BIPOLAR PATTERNS OF BIOTIC INTERCHANGE 309

stricted to polar regions and suggested the term antitropical.

Historically, antitropical patterns of marine nearshore invertebrates have been in- terpreted as the results of dispersal events (Forbes 1846; Darwin 1859). The role of vicariance (Nelson and Platnick 1981; Wiley 1981) in the origin of antitropical distributions is seldom considered or explored (but see Nelson [1985] and White [1986] for examples from marine fishes). The reasons for this are several. Foremost, the life cycle of most marine invertebrates includes a dispersal phase during which larvae or juveniles are subject to the vagaries of nearshore currents, often spending several weeks in the plankton (Jablonski and Lutz 1983, and references therein). In a single generation, or at the most a few years, it is possible for descendants of a single individual to disperse over thousands of kilometers (Scheltema 1971; Jablonski and Lutz 1983; Scheltema and Wil- liams 1983). Moreover, the major contiguous coastlines of the world tend to run in a north- south direction, as do their associated boundary currents (e.g., the California, Benguela, Peru, and Canary currents), and would seemingly provide excellent potential dispersal routes into lower latitudes. The barrier to dispersal along these routes is the tropics with its high surface-water temperatures and equatorial current systems. This tropical barrier predates the origin of many taxa that exhibit bipolarity.

To support a vicariance hypothesis for the origin of antitropicality, a temperate taxon must show evidence of having been divided into northern and southern components by the origin- of the tropics, by subsequent cooling and warming cycles, or by being carried from one hemisphere to the other on the margin of a plate or plate fragment. To be divided by the origin of the tropics, a taxon would have had to originate before the Cretaceous (> 144 Ma) (Kauffman and Johnson 1988). Ev- idence for a Tertiary cooling of the tropics is controversial (see Adams et al. 1990). Re- cently, however, Adams et al. (1990) have concluded that there has been little change in sea-surface temperatures at low latitudes during most of the Tertiary (at least the Early

Eocene to Middle Miocene) and that temperatures have consistently ranged from 200 to 28?C. As Briggs (1987) pointed out, many antitropical patterns involve closely related species that show little morphological diver- gence, and thus argue for a relatively recent interchange. Moreover, a drop in tropical water temperatures that would allow for the establishment of temperate taxa in the low latitudes also would augment interchange between the northern and southern hemispheres, thereby confounding vicariance and dispersal processes.

Interchange via plate margins or plate frag- ments would have had to occur before the Late Miocene in California (Howell et al. 1985), and could have transported taxa between 2,500 and 3,800 km northward from origins in lower latitudes (Champion et al. 1981; Champion and Howell 1986). In temperate South America, terrane accretion had mostly ended by early Tertiary time (Howell et al. 1985). Although plate riding provides a dynamic platform on which to bridge the tropics (at least in a northward direction), it does not alleviate the thermal barrier that the tropics represent to temperate species.

There is little doubt that both vicariance and dispersal occur within the marine realm. Moreover, the processes that fragment some taxa also can break down barriers against dispersal of others. As Hallam (1981: p. 340) pointed out, they are "two sides of the same coin ... the creation of the Central American isthmus and Middle Eastern closure of the Tethys promoted vicariance among marine organisms and dispersal among terrestrial organisms."

In this paper I review and examine the role biotic interchange has had in producing antitropical patterns in the eastern Pacific Ocean, with emphasis on the rocky shore fauna. Many antitropical patterns have been recognized for over 125 years; however, the processes that have been proposed to account for these patterns have not been critically assessed in view of the fossil record of interchange. Incorpo- ration of the fossil record into studies of marine biotic exchange is essential and provides needed constraints on the recognition of po-

310 DAVID R. LINDBERG

Californiaf

N. Equatorial S. Equatorial 4%

Peru

FIGURE 1. Holocene coastline and currents of the eastern Pacific Ocean. Stippled areas, temperate coastlines (in the sense of Hedgpeth 1957).

tential processes that have facilitated interchanges.

Inherent in any biogeographic study are assumptions of relationship (e.g., gene flow among individuals of a population or common ancestry of taxa that compose a clade; for an overview, see Wiley [1981]). Most of the exemplary taxa discussed here lack a modern phylogenetic treatment. Thus, sister taxa status (i.e., two taxa that share a common an- cestor) has not been demonstrated for many of the classical bipolar taxa, and there remains the danger of confusing common ancestry with convergence. Further studies of bipolar species, based on explicit phylogenetic hypotheses, are sorely needed and will undoubtedly contribute to further resolution of the phenomenon of antitropicality in nearshore marine faunas.

Physical Settings In the northeastern Pacific Ocean the tem-

perate nearshore region (boreal + warm temperate in the sense of Hedgpeth [1957]) stretches from Bering Strait (65?N) to Bahia Magdalena, Baja California Sur, Mexico (25?N)

30- North South

25

20 4 C: a) o 15- (I, a,

10-

5 -u August -9-February

060 40 20 6 20 40 -60 Degrees Latitude

FIGURE 2. Maximum (August) and minimum (February) sea-surface temperatures for the nearshore eastern Pacific Ocean. Data from Sverdrup et al. (1942).

(Fig. 1). In the southeastern Pacific, this region occurs between Punta Aguja, Peru (4?S), and Chiloe, Chile (42?S) (Fig. 1). Today both coastlines are relatively straight and exposed, but during the early Neogene both regions were marked by numerous embayments (Cole and Armentrout 1979; Dunbar et al. 1990).

Both temperate regions are flanked by equatorial flowing boundary currents; the California current in the north and the Peru current in the south (Fig. 1); both transport cooler surface waters into the lower latitudes. Maximum and minimum mean sea-surface temperatures for these coastlines are presented in Fig. 2. Strong northwesterlies in the north and southwesterlies in the south drive extensive upwelling systems off both coasts, further cooling nearshore conditions; the presence of upwelling along the coasts substantially increases nearshore productivity, and both regions support extensive marine shore faunas and floras (Brink et al. 1983; Huyer 1983).

Pattern In the New World, antitropical patterns are

found in almost all animal and plant groups, terrestrial and marine (Ekman 1953; Raven 1963; Pielou 1979, and references therein). In the marine realm, bipolarity is found in most plant and animal groups. Many algal taxa exhibit antitropical distributions along the eastern Pacific margin. Santelices (1980) concluded that 43 (11%) temperate South American species had global bipolar distributions, and an additional 27 species (7%) were bipolar and endemic to the eastern Pacific margin. The


giant kelps Macrocystis integrifolia and Mac- rocystis pyrifera are especially conspicuous in both the temperate north and south (Hedg- peth 1957; Estes and Steinberg 1988). Many examples of antitropical distributions have also been reported for planktonic organisms including foraminifera (Lipps 1979), euphausiids (Brinton 1962), and radiolarians (Stanley 1981).

Among marine mammal taxa, bipolarity is especially pronounced in the Pacific Ocean. Otariid seals of the genus Zalophus are found in the northeastern Pacific (and possibly northwestern Pacific) and at the Galapagos Islands (King 1983). Fur seals (genus Arcto- cephalus) are also bipolar with a high diversity in the south (8 species) and a single species in the north (King 1983). In the Phocidae, only the elephant seals show generic level antitropicality with Mirounga angustirostris in the north and Mirounga leonina in the south (King 1983).

Many examples of antitropicality have come from fishes (Regan 1916; Berg 1933; Norman 1937; Hubbs 1952; Randell 1982; Nelson 1985; White 1986; Briggs 1987), and it has been ich- thyologists who have become the leading proponents of the various theories to account for antitropical distributions (see review by Briggs 1987).

Crustacean workers were among the first invertebrate zoologists to comment on taxo- nomic similarities between the temperate regions of the eastern Pacific. Dana (1852) noted generic level similarities in the crustacean faunas of California and Chile. Ekman (1953) pointed out that the genus Lithodes was represented by eight species in the North Pacific Ocean and a single species in the Mag- ellanic province in the South Pacific, and Garth (1957: p. 5), in a treatment of the bra- churian crustaceans of Chile, commented on the "biological reflection in the number of analogous species inhabiting the two hemispheres." His examples included species be- longing to the genera Cancer, Taliepus, Hemi- grapsus, and Cyclograpsus. Nations (1979) in a study of the taxonomy and biogeography of cancerid crabs concluded that the genus Can- cer originated in the North Pacific and migrated into the southeastern Pacific during

the Pliocene, and from there it subsequently dispersed to New Zealand and Australia via the West Wind Drift.

Molluscs are another group whose antitropical distributions were noticed early on. Dall (1909) published the first systematic review of the molluscan fauna of the Peruvian Province, and discussed the similarities between the oceanographic, geographic, and climatic settings of the temperate west coasts of North and South America. Dall concluded that the fauna of the Peruvian Province was chiefly southern in origin, and that the intertidal gastropod genera Tegula, Thais, Acan- thina, and the bivalve genus Protothaca had migrated through the tropics as far north as Alaska and west to Japan. Although bipolar distributions for the genera Thais and Proto- thaca are suspect today, bipolar distributions for the taxa Tegula (Chlorostoma) (Hickman and McLean 1990) and Acanthina (southeastern Pacific)lAcanthinucella (northeastern Pacific) (Wu 1985; Vermeij pers. comm.) remain viable. After a study of the intertidal molluscan fauna at Iquique, Chile, Marincovich (1973) concluded that 49 intertidal genera out of a possible 68 (72%) were common to the Chil- ean and Californian provinces.

Subtidal molluscs also show antitropicality. Smith (1970) discussed the antitropical distributions of the ranellid gastropods Fusitriton and Argobuccinum. In the eastern North Pa- cific Fusitriton occurs from the intertidal (in the Gulf of Alaska) to depths in excess of 2,500 m in the Channel Islands of southern Cali- fornia. Species are unknown south of Baja California in the North Pacific. In the southern hemisphere, however, Fusitriton species are found in South America (4-580 m), New Zealand (40-1,100 m), Australia (100-500 m), and southern Africa (60-600 m). On the outer continental shelf and slope of the Pacific Rim, the trochacean gastropod genus Bathybembix (sensu stricto) is represented by one species in Japan, one in the northeastern Pacific, and two off Chile and Peru (McLean 1982). Bathy- bembix first appears at the Eocene-Oligocene boundary in the northeastern Pacific (Hick- man 1980). The deep-water turrid genus Afor- ia is also primarily bipolar (North Pacific and Antarctica), but it is also present in the Plio-


cene Esmeraldas Beds in northwestern Ec- uador (Olsson 1964), and Keen (1971) lists Aforia goodei as occurring from Queen Char- lotte Sound, British Columbia, Canada, to southern Chile in 1,220 to 1,950 m.

Soot-Ryen (1959: p. 77) reviewed the bivalve fauna of Chile and concluded that "Apart from more widely distributed genera, the remainder shows close connection with the eastern and western Americas and the Antarctic." In his review of the Mytilidae of the world, Soot-Ryen (1955) discussed the antitropical distribution of Mytilus edulis along the eastern Pacific. In North America, this taxon ranges from the Arctic Ocean to Cabo San Lucas, Baja California Sur, Mexico, and from Valparaiso to the Strait of Magellan, Chile. Although the genus Philobrya is not discussed by Soot-Ryen (1959), Vermeij (pers. comm.) has pointed out that it is another likely bipolar taxon with at least three species in the Chilean fauna and a single species, P. se- tosa, in North America (Alaska to the Gulf of California).

Several gastropod limpet groups also show strong antitropical patterns. In the family Fis- surellidae the genera Fissurellidea and Fissu- rella reach their highest diversity in the southern hemisphere and have single outliers in the northeastern Pacific (McLean 1984a,b). In the Patellogastropoda, the Scur- riini exhibit an antitropical distribution, with nine species in Chile and a single species in California (Lindberg 1988a), and Vermeij (pers. comm.) has suggested the possibility that the temperate pulmonate limpet taxa, Lir- iola, of the northeastern Pacific and Pachysi- phonaria of the temperate southern Pacific are sister taxa.

Marcus (1959) in a review of the Opistho- branchia of Chile discussed antitropical patterns represented in the fauna, and Williams and Gosliner (1979) discussed the antitropical distribution of the nudibranch genus Acan- thodoris (see below).

The history of eastern Pacific temperate fauna is well enough known to allow for the development of a historical perspective for several patterns discussed above. Herm (1969), in a study of the Pliocene and Pleistocene faunas of northern and middle Chile, sug-

gested that biotic exchange between the Cal- ifornian and Chilean provinces occurred during the Pliocene. During the Miocene, the Chilean fauna (as exemplified by the fauna of the Navidad Formation) showed strong affinities with the tropical Atlantic (Philippi 1887; Steinmann 1896), based on gastropod genera with Tethyan affinities such as Cassis, Fusus, Oliva, and Voluta. Extinction of this fauna at the Mio-Pliocene boundary was followed by the development of a Chilean fauna with stronger North Pacific affinities. The Plio-Pleistocene boundary was marked by regional cooling and the development of the distinctive, modern Chilean fauna (see also Zinsmeister 1977). Taxa with tropical and subtropical affinities (e.g., Anadara, Dosinia, Isognomon) were further restricted to low latitudes, whereas several taxa that first appeared in the Pliocene (e.g., Fissurella, Meso- desma, Mulinia) underwent impressive radiations. Other taxa such as Chlamys and Chorus endured substantial reductions in species diversity. Herm (1969) also reported a second, smaller wave of immigration from the northern portion of the Panamic molluscan province at the beginning of the Pleis- tocene, but these species retreated toward the equator during the middle Pleistocene.

Herm (1969) proposed that the formation of the Humbolt Current (=Peru Current) was partially responsible for the extinctions at the Mio-Pliocene boundary; however, he did not address possible mechanism(s) for the introduction of North Pacific taxa into the region during the Pliocene.

Smith (1970) used the fossil record of Ar- gobuccinum and Fusitriton to document the dispersal of these two genera from the North to South Pacific Oceans. Smith concluded that Argobuccinum most likely migrated during the Oligocene or Miocene and was established in the southern oceans by the mid-Miocene; it subsequently became extinct in the North Pa- cific. North to south dispersal of Fusitriton occurred much later, probably during the Plio- Pleistocene or Pleistocene. Smith considered several different processes that may have transported these taxa across the equator, including the use of upwelling cells and southward extensions of the California Current by


cool-water taxa to bridge the tropics, tropical submergence, and trans-Pacific migration via equatorial currents.

DeVries (1984) also remarked on the Mio- cene to Pliocene faunal change that took place in Chile, pointing out that the disappearance of tropical taxa such as Architectonica, Conus, Cypraea, Distorsio, and Ficus was followed by the appearance of a distinct Chilean fauna dominated by muricids and venerids. It was also during the Pliocene that several northeastern Pacific taxa (e.g., Chama, Crenomytilus, Cryptomya) first appeared in northern Peru (DeVries pers. comm.). By the end of the Plio- cene, 50% of the fauna became extinct and a second wave of immigrant taxa (e.g., Argo- pecten) appeared in Chile.

Three rocky intertidal limpet taxa appear to have migrated south to north unlike the above north-to-south examples (Lindberg 1988a). The genus Fissurella (in the strict sense) is one of the youngest taxa in the Fissurellidae and first appeared in the Pliocene in Chile (Herm 1969; McLean 1984b). Today there are 13 species in the southeastern Pacific and single outliers in the Caribbean and northeastern Pacific (McLean 1984b). The northeastern Pacific species, Fissurella volcano, did not appear until the early Pleistocene, in southern California (Lindberg 1988a), but after its first occurrence it is a common and abundant species in most subsequent Pleistocene faunas (Grant and Gale 1931; Valentine 1961). An- other fissurellid, Fissurellidea bimaculata, also shows a similar pattern. It is the only northeastern Pacific member of a southern hemisphere group distributed from South America to southern Africa (McLean 1984a). And like Fissurella volcano, after its initial appearance during the early Pleistocene in California, it also is a common and abundant species in many subsequent Pleistocene assemblages (Grant and Gale 1931; Valentine 1961).

The patellogastropod taxon Scurriini also shows an antitropical distributional pattern with the suggestion of a Pliocene migration (Lindberg 1988a) from south to north. The Scurriini, and its sister taxon Lottiini, are nu- merically and ecologically diverse clades along the eastern Pacific margin (Lindberg 1988b). Within the Scurriini, there are at least

eight species of Scurria in the Peruvian molluscan province and a single Holocene species of Discurria in the Californian molluscan province. There are over 30 temperate species of Lottia and Tectura in the northeastern Pa- cific, but none in the temperate southeastern Pacific.

The clades Scurriini and Lottiini first appear in the Pliocene in Chile and California, respectively. The first members of Discurria, the sister taxon of the Chilean genus Scurria (Lindberg 1990), also appear in the Pliocene in California at San Diego (Lindberg 1988a), but it is not until the early Pleistocene that Discurria becomes an ubiquitous component of rocky-shore assemblages. Moreover, in the early Pleistocene in California there are at least two species of Discurria, although only a single species survives today (Lindberg 1988a). This species, D. insessa occurs on the stipes of the brown algae Egregia menziesii, and the shell morphology is substantially modi- fied for this habitat. This specialization is analogous to that of Scurria scurra that occurs on the stipes of Lessonia nigrescens in Chile.

Other gastropod taxa that show antitropical distributions and may have migrated between hemispheres include the taxon Alia that is represented by only two species, A. carinata in the northeastern Pacific and A. unifasciata that ranges from Rio de Janiero, Brazil, south and then north to Peru (Radwin 1977). Alia carinata first appears in the early Pleistocene Santa Barbara Formation of southern Califor- nia; fossil occurrences of A. unifasciata are not known. Members of the archaeogastropod taxon Tegula (Chlorostoma) are well represented in Japan, California and Chile (Mc- Lean 1970). First occurrences include the Miocene in Japan and California (Hickman and McLean 1990), followed by Pliocene occurrences in Chile (Herm 1969). Olsson (1964) described two species of the buccinid genus Kelletia from the Pliocene Esmeraldas Beds of northwestern Ecuador. Kelletia species first appear in the Miocene of California (Grant and Gale 1931), and today the genus is represented by only a single species in Califor- nia. Vokes (1988) found three muricid species in the same deposits that had northern Cal- ifornia-Japan affinities: Ceratostoma notiale,


Pteropurpura marksi, and P. ecuadoria. How- ever, neither of these immigration events appears to have been successful in the long term since no descendants of these taxa occur in the region today.

It is also interesting that the arrival of both phocid and otariid seals in the southeastern Pacific also dates from the Early Pliocene (5 Ma; Muizon 1978, 1981), although they have been present in the northeastern Pacific for at least the last 15 m.y. (Repenning et al. 1979; Barnes et al. 1985; Warheit and Lindberg 1988).

Using the above fossil histories, it is possible to delimit the timing of biotic exchange between the two hemispheres. These data suggest that there are at least two major events. The first in the Pliocene, exemplified by the appearance of the molluscan taxa Chama, Crenomytilus, Cryptomya, and Tegula (Chloro toma) in the southern hemisphere and Dis- curria in the north, and a second early Pleis- tocene event marked by the appearance of Fusitriton and Argopecten in Chili and the arrival of Fissurella, Fissurellidea, and possibly Alia, in California. Clearly, taxa have moved from both south to north, and north to south across the tropical eastern Pacific. Moreover, exchange taxa have represented a diverse array of habitats from sandy beaches to exposed rocky coasts.

Process

Do the above patterns and their histories support dispersal or vicariance models for the different events? Dispersal and vicariance mechanisms invoked to account for antitropical distributions are presented in Table 1, and most have been reviewed by Springer (1982), Nelson (1985), and Briggs (1987). The only possible mechanism overlooked by these authors has been Smith's (1970) suggestion that marine invertebrate larvae carried toward the equator by boundary currents could then be carried west by equatorial currents, and finally toward the pole by the western current systems. Once again in the temperate regions, easterly flowing currents in the high latitudes could transport the species back across the ocean basin, providing an antitropical distribution along a continuous north- south coastline. Smith recognized the prob-

TABLE 1. Mechanisms proposed to account for antitropicality in marine taxa.

Phenomenon/mechanism Reference

Dispersal Glacial cooling Forbes 1846; Darwin

1859; Hubbs 1952; Brinton 1962

Trans-Pacific currents Smith 1970 Submergence Smith 1970 Regional perturbations This paper

Vicariance Extinction Theel 1885; Rehder

(Competition) 1980; Briggs 1987 Extinction Rehder 1980; Kay 1980

(Loss of habitat) Plate fragmentation Nelson 1985 Island integration Rotondo et al. 1981;

Springer 1982 Warming White 1986

lems associated with this mechanism and cited the great distances involved, the high temperatures, and the complex current interactions that would need to be breached by the larvae. Evidence cited by Smith in favor of this mechanism is the occurrence of the antitropical taxon, Fusitriton midwayensis at Midway Island in the central Pacific.

The diversity of taxa, habitats, and life history strategies, as well as the bidirectionality and timing of the exchanges argues against a single causal event or mechanism. For example, some taxa such as Fusitriton, Argobuc- cinum and Aforia appear to have crossed the tropics via submergence (Smith 1970). This mechanism is not available to other taxa such as the brown alga, Macrocystis, which would have had to disperse as rafting adult plants, or possibly as pelagic spores, in illuminated surface waters (Reed et al. 1988). Moreover, the dispersal of the brown alga, Macrocystis, between hemispheres would seemingly re- quire both nonlethal temperatures (<19?C; Hay 1990) and conducive current patterns through the surface waters of the tropics, whereas a benthic invertebrate, such as Fu- sitriton, could literally crawl between temperate regions by submerging to a depth of less than 200 m to maintain ambient temperatures of less than 13?C (Sverdrup et al. 1942).

The ability of nearshore invertebrates to cover large distances relatively rapidly in geologic time is exemplified by the distri-


bution of taxa in regions of western North America that were glaciated by the Cordil- leran Glacier Complex (roughly the coastline from the westernmost Aleutian Islands to Pu- get Sound, Washington [Flint 1971]). During the last 15 k.y., intertidal and shallow subtidal taxa from regufia south of Puget Sound have recolonized this formerly glaciated area. Even allowing for possible rocky coast refugia along the coast of Beringia, it is not unreasonable that taxa with and without pelagic larval phases have dispersed more than 2,000 km since the glaciers retreated. This would re- quire a dispersal rate of only 133 m/year. Moreover, the recolonization of the Aleutian Islands, where there are substantial distance and depth barriers between major island groups, has produced no significant differ- ence in the distributions of molluscs with either pelagic or nonpelagic development (Ver- meij et al. 1990). Given amenable temperature and current conditions, the dispersal of nearshore marine invertebrates (both with pelagic and nonpelagic development) would appear instantaneous in geologic time.

For most nearshore eastern Pacific margin taxa, the various vicariance mechanisms that have been proposed to explain antitropical distributions (Table 1) can be rejected. The fossil record of many of the taxa that have antitropical distributions indicates that they first appear at higher latitudes, not in the equatorial region (e.g., Fusitriton, Argobucci- num, Fissurella, Cryptomya, Argopecten, Tegula (Chlorostoma)). Thus, the scenario of extinction of an ancestral equatorial population (by either competition or habitat loss) and the formation of two high-latitude descendant taxa is not supported by the available fossil record. The timing and geological settings during the establishment of antitropical distributions argue against both plate fragmentation and island integration as likely causal mechanisms (see also Newman 1979; Gosliner 1987a).

White (1986) proposed that a Miocene warming, in a formerly cooler tropical eastern Pacific, divided many low-latitude taxa into northern and southern components. However, Briggs (1987) pointed out that temperatures in the region before the warming

event were not as cool as required by White's model (see also Adams et al. 1990), and that the occurrence of numerous isolation events (as reflected by the different levels of morphological differentiation seen in different taxa with antitropical distributions taxa) argues against a single event.

Dispersal across the tropics remains the most likely mechanism for the establishment of most of the antitropical distributions discussed above. However, the same patterns of taxon distributions, habitat utilization, life history diversity, directions of movement, and timing of the exchanges that falsify certain vicariance models also constrain dispersal models. For example, although the glacial cooling hypothesis could account for the Plio- Pleistocene pulse of exchange seen in the fossil records of California and Chile, it cannot be invoked to explain the larger Pliocene exchanges (see also Lipps [1979] for a discussion of Miocene formaniferal exchanges). The submergence model remains potentially valid for subtidal taxa, especially those with nonpelagic development, and could have operated during most of the Neogene. The trans-Pa- cific dispersal model is unlikely for the reasons given by Smith (1970) and reiterated above. This is not to deny that once northern taxa succeeded in making it into the southern hemisphere, the easterly flowing West Wind Drift augmented exchange between temperate Australia, New Zealand, South America and southern Africa. The distribution of the nudibranch genus Acanthodoris is a likely case. The genus is distinctly antitropical with its greatest diversity in the temperate North Pa- cific Ocean where 14 species have been reported: 2 northwestern Pacific species, 11 northeastern Pacific species, and 1 northeastern Atlantic species (one species, A. pilosa, occurs in both the North Pacific and the North Atlantic) (Williams and Gosliner 1979; Gos- liner 1987a). There are 6-8 species in the temperate South Pacific Ocean: 3-5 southwestern Pacific species, 2 southeastern Pacific species, and 1 southeastern Atlantic species (Williams and Gosliner 1979; Gosliner 1987b). The presence of three parallel antitropical distributions (western Pacific, eastern Pacific, and eastern Atlantic) in a single genus is unusual


and begs the question, were the tropics breached by a member of this taxon in one, two, or three geographical regions? The lack of a continuous coastline in the western Pa- cific, and the apparently recent dispersal of A. pilosa over Arctic Canada into the North Atlantic (based on the lack of morphological differentiation between specimens found in the three regions), suggests that Acanthodoris most likely crossed the tropics along the eastern Pacific margin and was subsequently dispersed throughout the southern hemisphere by the West Wind Drift.

The Pliocene exchanges necessitate a model that does not depend on glaciation to cool the tropics and allows for interchange in both directions. Moreover, these exchanges re- quire a mechanism that would provide both cooling and disrupt the regional current patterns within the region. The closing of the Panamic portal provided both conditions and is consistent with the timing of interchange.

Using biogeographic and isotopic studies of Foraminifera from Deep-Sea Drilling Proj- ect sites, Keigwin (1978, 1982) concluded that the closing of the Panamic Portal about 3.1 Ma had substantial effects on regional surface water temperatures and current patterns. Re- cently, Duque-Caro (1990) has examined the Neogene evolution of the Panama Seaway using foraminiferal biostratigraphy. Duque- Caro found that during the Late Miocene cool, well-aerated surface waters of the California Current were present along the Pacific coastal region of southern Central America and northwestern South America. These conditions began about 9.2 Ma (Late Miocene) and persisted for about 5.5 m.y. until about 3.7 Ma (Early Pliocene). Current patterns in the region also would have been substantially al- tered during the Late Miocene and earliest Pliocene by shallowing across the portal and the partial emergence of the Serranian de San Blas-Darien that disrupted and restricted the flow of the Atlantic and Caribbean currents into the adjacent Pacific region. This emer- gent island probably also served as the route for the earliest interchange (9.3-8 Ma) between North and South American terrestrial faunas (Marshall 1985; Webb 1985).

Weaver (1990) has also explored the impli-

cations of the closing of the Panamic portal on regional current and climate patterns. Weaver draws an analogy between the Leeu- win current, a poleward-flowing eastern boundary current along the coast of Western Australia, and the eastern boundary currents along the Pacific coasts of North and South America. In the Australasian situation, throughflow from the western Pacific via the Indonesian Archipelago maintains this anomalous eastern boundary current. Weaver believes that throughflow via the Panamic portal had an analogous effect in the tropical eastern Pacific, causing the California current to flow toward the North Pole, suppressing upwelling, and making the climate in Baja California and California both milder and wetter then today. As the Panamic portal closed, the California current would flow toward the equator and upwelling would in- tensify; Weaver proposed a similar scenario for the South American coast as well.

Clearly, the uplift and complete emergence of the Panama Isthmus by 3.1 Ma (Keigwin 1982) is a major tectonic event in the region. The closing of the Panamic portal caused perturbations of both nearshore temperature and current patterns, and occurred just before the earliest evidence that biotic interchange had taken place between the temperate regions of the eastern Pacific. This event and the associated oceanographic phenomenon provide an appealing scenario to explain the antitropical distribution patterns that appear in the Pliocene. Further studies, especially finer correlations between protist and invertebrate fossil records, are needed.

Although this model provides a mechanism for the origin of antitropical distributions in the northeastern Pacific during the Pliocene, it is not useful for explaining Plio- Pleistocene interchanges in the eastern Pa- cific. In this case, the glacial cooling model remains viable. The concurrence of the onset of Pleistocene glaciation with a second, smaller pulse of biotic interchange in the eastern Pacific can be demonstrated in fossil assemblages in both Chile (DeVries 1984) and Cal- ifornia (Lindberg 1988a).

A glacial model requires the expansion of the temperate region, at the expense of the


tropics, during periods of glacial maxima. This effectively lowers the distance between temperate regions on either side of the equator and facilitates fortuitous interchange between the two temperate regions. However, on the basis of zooplankton microfossils, Moore et al. (1981) concluded that the polar faunas expanded toward the equator during glacial maxima (i.e., 18 Ka), but the tropical regions remained relatively unchanged. That is, latitudinal compression occurred in the subpolar and subtropical faunas, but the tropical barrier remained intact. Of possibly greater importance, however, was their find- ing of increased upwelling activity in eastern boundary currents and in eastern equatorial areas.

Dawson (1946) and Hubbs (1948) were among the first workers to demonstrate a correlation between the distribution of cool-temperate organisms and the occurrence of upwelling along the warm-temperate cost of North America. Hubbs (1948) reported cold- water fish common to central California as well as intertidal occurrences of the abalone Haliotis rufescens and urchin Stronglyocentrotus franciscanus along the Baja California coast in upwelling areas. Emerson (1956) found cool- temperate species such as the coral Balano- phyllia elegans, the gastropod Acmaea mitra, the crab Haplogaster cavicauda, and the isopod Idothea stenops in the intertidal zone adjacent to an upwelling region at Punta Santo Tom'as, Baja California Norte, Mexico. Also present at this site were intertidal algal species that typically occurred in central California. Em- erson (1952, 1956) and Valentine (1955) suggested that the presence of cool-temperate organisms in nearshore upwelling regions was responsible for the presence of thermally anomalous faunas in the Pleistocene in Baja California, Mexico.

The localization of cold-water organisms in upwelling regions along the coast of Baja Cal- ifornia, Mexico, provides a neontological model for the propagation of temperate taxa along subtropical and tropical coastlines toward the equator (Fig. 3). Upwelling cells along the coast are typically stable in ecological time and space (Huyer 1983) and provide refugia for temperate species. Individuals that

FIGURE 3. Upwelling regions along the Pacific coast of, Baja California, Mexico. These regions are characterized by fauna and flora more typical of central California. After Dawson (1951).

occur at these locales are not restricted to single generations or size classes, although it is possible that many of these extralimital taxa are present only as "pseudopopulations" (in the sense of Mileikovsky 1971); that is, populations whose viability depends on the recruitment of larvae from populations occurring in other areas. Undoubtedly, the presence of these populations reduces the distances across warm-water barriers, and as Mileikov- sky (1971: p. 203) pointed out "secures out- posts for invasion of new biotopes when favorable conditions occur." In the present case, favorable conditions would certainly include increased upwelling activity along the temperate eastern Pacific coastline and in eastern equatorial areas.

Sea-level changes that would accompany glacial periods would probably affect the po- sition and intensity of upwelling cells. Up- welling centers are strongly influenced by


coastal and submarine topography (Brink 1983). For example, upwelling areas along the Pacific coast of Baja California (Fig. 3) are closely associated with prominent headlands (Dawson 1951; Emerson 1952). At the height of the Wisconsian glaciation (18 Ka) sea level would have been up to 100 m lower than at present (Vail and Hardenbol 1979; Haq et al. 1987), dramatically changing coastal and nearshore topography. Whether a 100-m drop in sea level would have increased or de- creased the number of potential upwelling sites along the eastern Pacific margin is not known. However, falling sea levels during glacial periods further complicates our un- derstanding of upwelling patterns during these periods of probable interchange.

Discussion

Antitropical distributions occur in a diverse array of marine invertebrate, vertebrate, and plant groups in the eastern Pacific Ocean. Table 2 summarizes the direction, subsequent speciation, and the time of biotic interchange between the temperate regions of the northeastern and southeastern Pacific Ocean. The available data suggest an asym- metrical Pliocene interchange with the bulk of the dispersing species going south. In contrast, the Pleistocene interchange appears to be symmetrical with approximately equal numbers of the taxa going both south and north. Subsequent speciation rates also differ; taxa going south show a higher species diversity. This may, however, be only a func- tion of time, since the vast majority of species that went south did so in the Pliocene. Ver- meij (pers. comm.) has pointed out that in many cases of biotic interchange the asymmetry of the immigration favors regions that have previously experienced substantial extinctions. The southward asymmetry in the eastern Pacific interchange is consistent with this model. Both Herm (1969) and DeVries (1984) have commented on the extinctions within the Chilean fauna during the Late Micocene and Early Pliocene, and it is im- mediately after these extinctions that the Chilean fauna takes on a more North Pacific character.

Available geologic and paleontological ev-

TABLE 2. Summary of biotic interchange between the northeastern and southeastern Pacific Oceans; data are for taxa discussed herein. n, number of species; m, mean species diversity; %, percentage of all migration taking place during specified time period; N/A, no time resolution for migration event. Taxa that are represented by the same species in both regions (e.g., Macrocystis, Myti- lus) are not included.

Immigrant Direction of species Pliocene Pleistocene migration (n) diversity (m) migration migration

North to south (15) 2.2 species 9 (90%) 2 (40%) South to north (4) 1.25 species 1(10%) 3 (60%) Unknown (1) 1 species N/A N/A

idence does not support vicariance as a process in the creation of these bipolar distributions, but instead favors biotic interchange between hemispheres. Moreover, the timing of these events suggests several breaches (both northward and southward) of the tropics rather than a single event. The congruence of some interchanges with major regional tectonic events and others with Pleistocene glaciations is not surprising and argues for a plurality of mechanisms. In the case of the Pliocene interchanges, Hallam's (1981: p. 340) point that vicariance and dispersal are "two sides of the same coin" appears to apply even within a single biotope. Although the closing of the Panamic portal produced a vicariance event that separated Caribbean and tropical eastern Pacific marine organisms, the perturbations to tropical current patterns caused by the emerging isthmus appears to have facilitated the interchange of temperate marine organisms between the northeastern and the southeastern Pacific Ocean. In the case of Pleistocene interchanges, simple cooling of the tropics does not appear to be sufficient to allow biotic interchange. Instead corollary changes in upwelling intensity, storm tracks, sea-level changes, etc., coupled with global cooling and compression of the temperate and subtropical zones, provided conditions that substantially increased the probability of crossing the tropics relative to previous and subsequent settings.

Habitat Availability. -A successful crossing of the tropics alone does not guarantee that a taxon will establish a viable antitropical distribution. As Hickman and Lindberg (1984) have pointed out, the success of long-range


dispersal events may depend heavily on availability of suitable settings and substrates. Active continental margins, in contrast to passive margins, are much more dynamic and often present a greater diversity of substrates and habitats to potential colonizers (Trenhaile 1987). However, this dynamic nature could also impede colonization events.

DeVries (1984: p. 487) has suggested that the transition of the South American Pacific Plate margin from subsidence to uplift produced "complete tectonic destruction of [certain] habitat[s]." Fore-arc basins, with their complex topography and varied habitats were replaced by long expanses of exposed sandy beaches and many of the "endemic oppor- tunistic species ... and immigrant taxa from the north took advantage of the vacated or newly created niches." Such a large-scale regional event completely reorganized habitats along the South American coast and would have provided new opportunities for some colonizers while prohibiting the establishment of others.

Extinctions and Radiations. -A colonizer's interactions with the physical environment are necessary prerequisites for interactions with the endemic taxa (i.e., getting there is only part of the problem). Once in a new community, interactions with the endemic components of the fauna and flora present a set of biotic hurdles that must be sorted out. Three generalized outcomes of biotic interchange can be envisioned: (1) interactions between the invading and endemic taxon lead to the extinction of the invading taxon, (2) interactions between the invading and endemic taxon lead to the extinction of the endemic taxon, or (3) nothing happens; both taxa coexist. Case 3 occurs most often.

Case 1 situations may have occurred, but the establishment of a population followed by extinction caused by interaction would be difficult to detect in the fossil record because of the rapidity with which the two events may occur. Olsson's (1964) report of Kelletia and Vokes' report of three muricid species, all with North Pacific affinities, in Pliocene deposits in northwest Ecuador may fall into this category. As reviewed by Vermeij (1987:

p. 411), evidence for case 2 (extinction of endemic taxa following interchange) among marine invertebrates is weak, and none of the antitropical distributions reviewed here have suggested that the arrival of a taxon in the adjoining hemisphere resulted in the extinction of an endemic taxon. Case 3 is the norm: invading and endemic taxa coexist.

There is also the question of subsequent speciation. Do invading taxa have a greater proclivity to speciate than do endemic taxa or the sister taxon (or population) that remains behind in the ancestral region? In contrast to the extinction models, the patterns of radiations are diverse but tend to be on the low side (Table 2). Marine mammals show both low and high speciation rates, although all taxa migrated from the northern hemisphere into the southern hemisphere. Al- though nine species of fur seals inhabit the southern hemisphere, only two species are in the northern hemisphere. Elephant seals, however, are represented by only two species, one in each hemisphere.

Algal species appear to have undergone little morphological differentiation since their arrival in the southern hemisphere. Macro- cystis is represented by the same two species in the north and south (Hedgpeth 1957; Estes and Steinberg 1988), and Santelices (1980) listed nine additional algal species with bipolar distributions. Similar nonradiation patterns in the southern hemisphere are found in the crab genus Lithodes and the gastropod genus Tegula; both are represented by many species (more than eight) in the northern hemisphere. In contrast to Tegula, the gastropod genus Alia, like elephant seals, is represented by only one species in each hemisphere.

There is no correlation between either habitat or ancestry and the patterns of radiations. The subtidal gastropods Fusitriton and Bathy- bembix show a nonradiation pattern, just as some rocky intertidal gastropod species. Within most gastropod clades, the invading taxa show low speciation rates. Although the genus Fissurella (s.s.) has sustained a radiation of 13 species in South America, in the northern hemisphere there is only a single immigrant species (McLean 1984b), and the genus


Fissurellidea is represented by a single immigrant species in North America, 2 species in South America (1 in Chile and 1 in Argen- tina), and a fourth species in southern Africa (McLean 1984a). Patterns in patellogastropod clades are similar. Even though the subclade Scurriini is a member of a clade (Lottiidinae) capable of tremendous radiations (as exemplified by intertidal limpet faunas throughout the world; Lindberg 1988b), it produced only two species upon arrival in California and one of them became extinct during the Pleistocene (Lindberg 1988a).

Community Structure. -Many of the examples of antitropical taxa discussed above are members of rocky shore communities. Tem- perate rocky shore communities (including California and Chile) were monographed on a global scale by Stephenson and Stephenson (1972). Their goal had been to establish a uni- versal zonation scheme that explained species distributions throughout the world. Subse- quent studies of rocky shore communities have demonstrated that intertidal species' distributions are seldom determined by tidal fluctuations but primarily by biological conditions (e.g., Connell 1972; Paine 1977; Lub- chenco and Menge 1978; Underwood 1979; Paine and Levin 1981; Dayton 1984; Sousa 1984; Underwood and Denley 1984). These and other studies have established that rocky shore communities are organized around a set of cascading interactions involving competition, predation, disturbance, and recruitment. Some of these processes are cyclic or periodic; others are stochastic and random.

A cursory comparison of the temperate rocky shore communities of California and Chile suggests strong similarities between regions (see also Orians and Paine 1983). Many of the ecological guilds of these two regions are often composed of similar taxa (Table 3). However, the strength of the interactions between members of these guilds may or may not be similar in these two regions. For example, although the kelp forests of both Chile and California are (1) composed of the same species of kelp (Macrocystis pyrifera), (2) grazed by the same genus of snails (Tegula spp.), (3) have similar competitive hierarchies among the alga species, (4) serve as habitats for sea

urchins (Loxechinus and Stronglyocentrotus, respectively), and (5) are subject to similar stochastic events (e.g., substantially reduced by winter storms, vagaries of recruitment), the strong interactions that structure these communities in California are not present in the Chilean system (Moreno and Sutherland 1982; Dayton 1985). Thus, although these similar communities are, in part, the products of interchange, only the taxa have immigrated; the linkages and interactions appear to be independent and locally derived.

One of the exceptions to this model is a set of cascading interactions among humans, Black Oystercatchers (Haematopus spp.), herbivorous gastropods, and algae. In both Cal- ifornia and Chile, these systems are composed of identical or closely related species that crossed the tropics (e.g., Homo sapiens, black oystercatchers, limpets), and the interactions as well as the strength of the interactions appear to be identical (Castilla 1981; Frank 1982; Lindberg et al. 1987; Marsh 1987). It is interesting to note that similar systems composed of less closely related taxa (southern Africa; Hockey and Branch 1984), or with weaker overall interactions (England; Lewis and Bowman 1975), also occur in the temperate regions of the eastern Atlantic.

Ekman (1953: p. 251) also recognized this "ecological similarity" and referred to it as the "bipolarity of analogous parallel phe- nomena." Orians and Paine (1983: p. 455) considered ecological convergence among kelp communities, algal turf assemblages, herbi- vore guilds, and anemone guilds along temperate rocky shores and concluded that "convergence may not even be identifiable in rocky shore communities for a complex of reasons," including the problem of biotic interchange between communities. Demonstration of convergence requires separate ancestry for the species, and ultimately the communities that they compose. Based on Table 3, it is evident that this requirement is not met for temperate eastern Pacific communities. Rather, each temperate community is a mosaic consisting of cosmopolitan species, species that share common ancestry, and species having independent origins within each region. For example, predatory sea stars appear to be in-


TABLE 3. Select species that have been identified as having strong interactions with other co-occurring taxa along temperate rocky shores of the eastern Pacific Ocean. Taxa were selected from the reviews of Castilla (1981) for Chile and Foster et al. (1988) for California. An asterisk indicates species thought to be involved in biotic interchange across the tropics. Approximate number of species are given in parentheses.

Guild Northeastern Pacific Southeastern Pacific

Predators Humans Homo sapiens Homo sapiens Otters Enhydra lutris Lutra felina Birds Larus glaucescens Larus dominicanus

H. bachmani* Haematopus ater* Fishes Sicyases sanguineus Crabs Cancer spp. (7)* Cancer spp. (3)* Gastropods Nucella spp. Concholepus concholepus Sea stars Pisaster ochraceus Heliaster helianthus

Pycnopodia helianthoides Meyenaster gelatinosus

Herbivores Gastropods Fissurella spp. (13)* Fissurella volcano*

Lottia & Tectura spp. (23) Scurria spp. (9) Littorina spp. (5) Littorina spp. (3)

Tegula spp. (5)* Tegula spp. (2)* Haliotis spp. (7)

Chitons chitons (15+) chitons (9) Urchins Strongylocentrotus spp. (3) Loxechinus sp.

Space Barnacles Balanus & Chthamalus Balanus & Chthamalus Bivalves Mytilus spp. (2)* Mytilus spp. (5)* Tunicates Pyura

Algae Laminaria

Lessonia Gigartina Gigartina Macrocystis* Macrocystis* Corallina Carollina Porhyra Porhyra Iridaea Iridaea Ulva* Ulva*

Durvillea Rhodymenina* Rhodymenina* Fucus

dependently derived in each region, whereas herbivorous littorinid snails are cosmopolitan in their distribution within both temperate and tropical regions. Although some herbivorous gastropods such as limpets share common ancestry between the northeastern and southeastern Pacific Ocean (Scurriini, Fis- surella) and are the products of interchange, other taxa (Lottia and Scurria) represent two separate radiations within different clades. Thus, interactions and linkages between el- ements of the community can result from constraint (common ancestry) and from ad- aptations to similar physical and ecological conditions in the temperate regions (convergence).

Acknowledgments I am indebted to G. Vermeij for the invi-

tation to participate in the Fourth Interna- tional Congress of Systematic and Evolution- ary Biology (ICSEB IV) Congressional Symposium, for thought-provoking discussions, for examples of biotic interchange, and for his patience. The manuscript was substantially improved by the criticism of L. Ma- rincovich, G. Vermeij, and K. Warheit. I also benefited from discussions and examples provided by J. Carlos Castilla, T. DeVries, J. Estes, T. Gosliner, C. Hickman, J. Lipps, J. McLean, D. Reed, L. Rosenfeld, and W. Sousa. T. De- mere provided resolution of age determina- tions for several southern California localities


for which I am most grateful. This is contri- bution no. 1533 from the University of Cal- ifornia Museum of Paleontology.

Literature Cited ADAMS, C. G., D. E. LEE, AND B. R. ROSEN. 1990. Conflicting

isotopic and biotic evidence for tropical sea-surface temperatures during the Tertiary. Palaeogeography, Palaeoclimatolo- gy, Palaeoecology 77:289-313.

BARNES, L. G., D. P. DOMNING, AND C. E. RAY. 1985. Status of studies on fossil marine mammals. Marine Mammal Science 1: 15-53.

BERG, L. S. 1933. Die bipolare Verbreitung der Organismen und die Eiszeit. Zoogeographica 1:449-484.

BRIGGS, J. C. 1987. Antitropical distribution and evolution in the Indo-west Pacific Ocean. Systematic Zoology 36:237-248.

BRINK, K. H. 1983. The near-surface dynamics of coastal upwelling. Progress in Oceanography 12:223-257.

BRINK, K. H., D. HALPERN, A. HUYER, AND R. L. SMITH. 1983. The physical environment of the Peruvian upwelling system. Prog- ress in Oceanography 12:285-306.

BRINTON, E. 1962. The distribution of Pacific euphausiids. Bul- letin Scripps Institution of Oceanography 8:51-270.

CASTILLA, J. C. 1981. Perspectivas de investigacion en estructura y dinamica de comunidades intermaveales rocosas de Chile central. II. De predadores de alto nivel trofico. Medio Ambiente 5:190-215.

CHAMPION, D. E., D. G. HOWELL, AND M. C. MARSHALL. 1981. Paleomagnetic evidence for 380 km of northwestward translation of San Miguel Island, Southern California Borderland. ESO, American Geophysical Union Transactions 62:855.

CHAMPION, D. E., AND D. G. HOWELL. 1986. Paleomagnetism of Cretaceous and Eocene strata, San Miguel Island, California, Borderland and the northward translation of Baja California. Journal of Geophysical Research 91:11557-11570.

COLE, M. R., AND J. M. ARMENTROUT. 1979. Neogene paleogeography of the western United States. Pp. 297-323. In Ar- mentrout, J. M., M. R. Cole, and H. TerBest, Jr. (eds.), Cenozoic Paleogeography of the Western United States (Pacific Coast Paleogeography Symposium 3). Society of Economic Paleon- tologists and Mineralogists; Los Angeles, California.

CONNELL, J. H. 1972. Community interactions on marine rocky intertidal shores. Annual Review of Ecology and Systematics 3:169-192.

DALL, W. H. 1909. Report on a collection of shells from Peru, with a summary of the littoral marine Mollusca of the Peruvian Zoological Province. Proceedings of the United States National Museum 37:147-294.

DANA, J. D. 1852. Crustacea. Part II. United States Exploring Expedition during the years 1883, 1839, 1840, 1841, 1842, under the command of Charles Wilkes, U.S.N. Vol. XIII. Philadelphia.

DARWIN, C. 1859. On the origin of species by natural selection, or the preservation of favoured races in the struggle for life. John Murray; London.

DAWSON, E. Y. 1946. Marine algae associated with upwelling along the northwestern coast of Baja California, Mexico. Bul- letin of the Southern California Academy of Sciences 44:57- 71.

DAWSON, E. Y. 1951. A further study of upwelling and associated vegetation along Pacific Baja California, Mexico. Journal of Marine Research 10:39-58.

DAYTON, P. K. 1984. Processes structuring some marine communities: are they general? Pp. 181-200. In Strong, D. R., Jr., D. Simberloff, L. G. Abele, and A. B. Thistle (eds.), Ecological Communities: Conceptual Issues and the Evidence. Princeton University Press; Princeton, New Jersey.

DAYTON, P. K. 1985. The structure and regulation of some South American kelp communities. Ecological Monographs 55:447- 468.

DEVRIES, T. 1984. The fate of Pliocene marine mollusks from western South America. Abstracts with programs, The Geo- logical Society of America 16(6):487.

DUNBAR, R. B., R. C. MARTY, AND P. A. BAKER. 1990. Cenozoic marine sedimentation in the Sechura and Pisco basins, Peru. Palaeogeography, Palaeoclimatology, Palaeoecology 77:235-261.

DURHAM, J. W., AND F. S. MAcNEIL. 1967. Cenozoic migrations of marine invertebrates through the Bering Strait region. Pp. 326-349. In Hopkins, D. M. (ed.), The Berling Land Bridge. Stanford University Press; Stanford, California.

DUQUE-CARO, H. 1990. Neogene stratigraphy, paleoceanogra- phy and paleobiogeography in northwest South America and the evolution of the Panama Seaway. Palaeogeography, Pa- laeoclimatology, Palaeoecology 77:203-234.

EKMAN, S. 1953. Zoogeography of the sea. Sidgwick & Jackson; London.

EMERSON, W. K. 1952. The influence of upwelling on the distribution of marine floras and faunas of the west coast of Baja California, Mexico. The American Malacological Union, An- nual Report, 1952:32-33.

EMERSON, W. K. 1956. Upwelling and associated marine life along Pacific Baja California, Mexico. Journal of Paleontology 30:393-397.

ESTES, J. A., AND P. D. STEINBERG. 1988. Predation, herbivory, and kelp evolution. Paleobiology 14:19-36.

FLINT, R. F. 1971. Glacial and Quaternary Geology. John Wiley and Sons; New York.

FORBES, E. 1846. On the connexion between the distribution of the existing fauna and flora of the British Isles, and the geological changes which have affected their area especially during the epoch of the great northern drift. Memoirs of the Geological Survey of Great Britain 1:336-432.

FOSTER, M. S., A. P. DE VOGELAERE, C. HARROLD, J. S. PEARSE, AND A. B. THUM. 1988. Causes of spatial and temporal patterns in rocky intertidal communities of central and northern Califor- nia. Memoirs of the California Academy of Sciences 9:1-45.

FRANK, P. W. 1982. Effects of winter feeding on limpets by Black Oystercatchers (Haematopus bachmani). Ecology 63:1352-1362.

GARTH, J. S. 1957. Reports of the Lund University Chile Ex- pedition 1948-49. 29. The Crustacea Decapoda Brachyura of Chile. Lunds Universitets Arsskrift, N.F. Avd. 2. Bd 53. 7:1- 130.

GOSLINER, T. 1987a. Biogeography of the opisthobranch gastropod fauna of southern Africa. American Malacological Bulletin 5:243-258.

GOSLINER, T. 1987b. Nudibranchs of southern Africa. Sea Chal- lengers; Monterey, California.

GRANT, U.S., IV, AND H. R. GALE. 1931. Catalogue of the marine Pliocene and Pleistocene Mollusca of California. Memoirs of the San Diego Society of Natural History 1:1-1036.

HALLAM, A. 1981. Response. P. 340. In G. Nelson and D. R. Rosen (eds.), Vicariance Biogeography: a Critique. Columbia University Press; New York.

HAQ, B. U., J. HARDENBOL, AND P. R. VAIL. 1987. Chronology of fluctuating sea levels since the Triassic. Science 235:1156-1167.

HAY, C. H. 1990. The distribution of Macrocystis (Phaeophyta: Laminariales) as a biological indicator of cool sea surface temperature, with special reference to New Zealand waters. Jour- nal of the Royal Society of New Zealand 20:313-336.

HEDGPETH, J. W. 1957. Marine biogeography. Pp. 359-382. In Hedgpeth, J. W. (ed.), Treatise on Marine Ecology and Paleo- ecology. Geological Society of America Memoir 67, Vol. 1.

HERM, D. 1969. Marines Pliozan und Pleistozan in Nord- und Mittel-Chile unter besonderer Beriicksichtigung der Entwick- lung der Mollusken-Faunen. Zitteliana 2:1-159.


HicKMAN, C. S. 1980. Paleogene marine gastropods of the Kea- sey Formation in Oregon. Bulletin of American Paleontology 78:1-1 12.

HICKMAN, C. S., AND D. R. LINDBERG. 1984. Relationship of molluscan biogeographic anomalies to changing settings on an active continental margin. Abstracts with programs, The Geo- logical Society of America 16(5):289.

HIcKMAN, C. S., AND J. H. McLEAN. 1990. Systematic revision and suprageneric classification of trochacean gastropods. Nat- ural History Museum of Los Angeles County, Science Series, Special Publication 35:1-169.

HocKEY, P.A.R., AND G. M. BRANCH. 1984. Oystercatchers and limpets: impact and implications. A preliminary assessment. Ardea 72:199-206.

HOWELL, D. G., D. L. JONES, AND E. R. SCHERMER. 1985. Tectono- stratigraphic terranes of the circum-Pacific region. Pp. 3-30. In Howell, D. G. (ed.), Tectonostratigraphic Terranes of the Cir- cum-Pacific Region. Circum-Pacific Council for Energy and Mineral Resources; Houston, Texas.

HUBBS, C. L. 1948. Changes in the fish fauna of western North America correlated with changes in ocean temperature. Journal of Marine Research 7:459-482.

HuBBs, C. L. 1952. Antitropical distribution of fishes and other organisms. Proceedings of the 7th Pacific Science Congress 3: 324-330.

HUYER, A. 1983. Coastal upwelling in the California Current system. Progress in Oceanography 12:259-284.

JABLONSKI, D., AND R. A. LUTZ. 1983. Larval ecology of marine benthic invertebrates: paleobiological implications. Biological Reviews of the Cambridge Philosophical Society 58:21-89.

KAUFFMAN, E. G., AND C. C. JOHNSON. 1988. The morphological and ecological evolution of Middle and Upper Cretaceous reef- building rudistids. Palaios 3:194-216.

KAY, E. A. 1980. Little worlds of the Pacific: an essay on Pacific basin biogeography. Harold L. Lyon Arboretum Lecture 9. Uni- versity of Hawaii; Honolulu.

KEEN, A. M. 1971. Seashells of tropical west America. Second edition. Stanford University Press; Stanford.

KEIGWIN, L. D., JR. 1978. Pliocene closing of the Isthmus of Panama, based on biostratigraphic evidence from nearby Pa- cific Ocean and Caribbean sea cores. Geology 6:630-634.

KEIGWIN, L. D., JR. 1982. Isotopic paleooceanography of the Caribbean and East Pacific: role of Panama uplift in late Neo- gene time. Science 217:350-353.

KING, J. E. 1983. Seals of the World. 2nd ed. Cornell University Press; Ithaca, New York.

LEWIS, J. R., AND R. S. BOWMAN. 1975. Local habitat-induced variations in the population dynamics of Patella vulgata L. Jour- nal of Experimental Marine Biology and Ecology 17:165-203.

LINDBERG, D. R. 1988a. Systematics of the Scurriini (New Tribe) of the northeastern Pacific Ocean (Patellogastropoda: Lotti- idae). Veliger 30:387-394.

LINDBERG, D. R. 1988b. The Patellogastrapoda. Malacological Review, Supplement 4:35-63.

LINDBERG, D. R. 1990. Systematics of Potamacmaea fluviatilis (Blanford): a brackish water patellogastropod (Patelloidinae: Lottiidae). Journal of Molluscan Studies 56:309-316.

LINDBERG, D. R., K. I. WARHEIT, AND J. A. ESTES. 1987. Prey preference and seasonal predation by oystercatchers on limpets at San Nicolas Island, California, USA. Marine Ecology Prog- ress Series 39:105-113.

LIPPS, J. H. 1979. Ecology and paleoecology of planktic foraminifera. Pp. 62-104. In Lipps, J. H., W. H. Berger, M. A. Buzas, R. G. Douglas and C. A. Ross (eds.), Foraminiferal Ecology and Paleoecology. Lecture Notes for Short Course No. 6. Society of Economic Paleontologists and Mineralogists; Houston, Tex- as.

LUBCHENCO, J., AND B. A. MENGE. 1978. Community develop-

ment and the persistence in a low rocky intertidal zone. Eco- logical Monographs 48:676-694.

MARCUS, E. 1959. Reports of the Lund University Chile Expe- dition 1948-49. 36. Lamellariacea und Opisthobranchia. Lunds Universitet Arsskrift, N.F. Avd. 2. Bd 55. 9:1-134.

MARINCOVICH, L., JR. 1973. Intertidal marine mollusks of Iqui- que, Chile. Natural History Museum of Los Angeles County, Science Bulletin 16:1-49.

MARSH, C. P. 1987. Impact of avian predators on high intertidal limpet populations. Journal of Experimental Marine Biology and Ecology 104:185-201.

MARSHALL, L. G. 1985. Geochronology and land-mammal bio- chronology of the transamerican faunal interchange. Pp. 49- 85. In Stehli, F. G., and S. D. Webb (eds.), The Great American Biotic Interchange. Plenum Press; New York.

McLEAN, J. H. 1970. Order Archaeogastropoda. Pp. 307-363. In Keen, A. M. (ed.), Sea Shells of Tropical West America. Second edition. Stanford University Press; Stanford, California.

McLEAN, J. H. 1982. Large archibenthal gastropods of central Chile: collections from an expedition of the R/V Anton Bruun and the Chilean shrimp fishery. Natural History Museum of Los Angeles County, Contributions in Science 342:1-20.

McLEAN, J. H. 1984a. Shell reduction and loss in fissurellids: a review of genera and species in the Fissurellidea group. Amer- ican Malacological Bulletin 2:21-34.

McLEAN, J. H. 1984b. Systematics of Fissurella in the Peruvian and Magellanic faunal provinces (Gastropoda: Prosobranchia). Natural History Museum of Los Angeles County, Contribu- tions in Science 354:1-70.

MILEIKOVSKY, S. A. 1971. Types of larval development in marine bottom invertebrates, their distribution and ecological signif- icance: a re-evaluation. Marine Biology 10:193-213.

MOORE, T. C., JR., W. H. HUTSON, N. KIpP, J. D. HAYS, W. PRELL, P. THOMPSON, AND G. BODEN. 1981. The biological record of the ice-age ocean. Palaeogeography, Palaeoclimatology, Palaeoecology 35:203-234.

MORENO, C. A., AND J. P. SUTHERLAND. 1982. Physical and biological processes in a Macrocystis pyrifera community near Valdivia, Chile. Oecologia 55:1-6.

MUIZON, C. DE. 1978. Arctocephalus (Hydrarctos) lomasiensis, subgen. nov. et nov. sp. un nouvel Otariidae du Mio-Pliocenene de Sacaco (P6rou). Bulletin de l'Institut Frangais d'Etudes Andines 7:169-188.

MUIZON, C. DE. 1981. Les vertebres fossiles de la formation Pisco (Perou), 1: Deux nouveaux Monachinae (Phocidae, Mammalia) du Pliocene de Sud-Sacaco. Travaux de l'Institut francais d'Etudes andines 22. (Recherche sur les grandes civilisation m6moire 6); Paris.

NATIONS, D. 1979. The genus Cancer and its distribution in time and space. Bulletin of the Biological Society of Washington 3: 153-187.

NELSON, G. J. 1985. A decade of challenge: the future of biogeography. Earth Sciences History 4(2):187-196.

NELSON, G. J., AND N. I. PLATNICK. 1981. Cladistics and Vicar- iance: Patterns in Comparative Biology. Columbia University Press; New York.

NEWMAN, W. 1979. On the biogeography of balanomorph barnacles of the southern ocean including new balanid taxa: a sub-family, two genera and three species. Proceedings of the International Symposium on Marine Biogeography and Evo- lution of the Southern Hemisphere 1978. 1:279-306.

NORMAN, J. R. 1937. Coast fishes. 2. The Patagonian Region. Discovery Reports 16:1-150.

OLSSON, A. A. 1964. Neogene mollusks from northwestern Ec- uador. Paleontological Research Institution; Ithaca, New York.

ORIANS, G. H., AND R. T. PAINE. 1983. Convergent evolution at the community level. Pp. 431-458. In Futuyma, D. J., and M.


Slatkin (eds.), Coevolution. Sinauer Associates; Sunderland, Massachusetts.

PAINE, R. T. 1977. Controlled manipulations in the marine intertidal zone and their contributions to ecological theory. Pp. 245-270. In Goulden, C. E. (ed.), The Changing Scenes in Nat- ural Sciences, 1776-1976. Special Publication 12, Academy of Natural Sciences of Philadelphia; Philadelphia, Pennsylvania.

PAINE, R. T., AND S. A. LEVIN. 1981. Intertidal landscapes: disturbance and the dynamics of pattern. Ecological Monographs 51:145-178.

PHILIPPI, R. A. 1887. Die tertiaren und quartaren Versteinerun- gen Chiles. Brockhaus; Leipzig.

PIELOU, E. C. 1979. Biogeography. John Wiley and Sons; New York.

POR, F. D. 1971. One hundred years of Suez Canal-a century of Lessepsian migration: retrospect and viewpoints. Systematic Zoology 20:138-159.

RADWIN, G. E. 1977. The family Columbellidae in the western Atlantic. Veliger 19:403-417.

RANDELL, J. E. 1982. Examples of antitropical and antoequatorial distributions of Indo-West Pacific fishes. Pacific Science 35:197- 209.

RAvEN, P. H. 1963. Amphitropical relationships in the floras of North and South America. Quarterly Review of Biology 38: 151-177.

REED, D. C., D. R. LAUR, AND A. W. EBELING. 1988. Variation in algal dispersal and recruitment: the importance of episodic events. Ecological Monographs 58:321-335.

REGAN, C. T. 1916. The British fishes of the subfamily Clupeinae and related species in other seas. Annals and Magazine of Natural History, Series 8 8:1-18.

REHDER, H. A. 1980. The marine mollusks of Easter Island (Isla de Pascua) and Sala y G6mez. Smithsonian Contributions to Zoology 289:1-167.

REPENNING, C. A., C. E. RAY, AND D. GRIGORESCU. 1979. Pinniped biogeography. Pp. 357-369. In Gray, J., and A. J. Boucot (eds.), Historical Biogeography, Plate Tectonics, and the Changing Environment. Oregon State University Press; Corvallis, Ore- gon.

ROTONDO, G. M., V. G. SPRINGER, G. A. J. SCOTT, AND S. 0. SCHLANGER. 1981. Plate movement and island integration- a possible mechanism in the formation of endemic biotas, with special reference to the Hawaiian Islands. Systematic Zoology 30:12-21.

SANTELICES, B. 1980. Phytogeographic characterization of the temperate coast of Pacific South America. Phycologia 19:1-12.

SCHELTEMA, R. S. 1971. The dispersal of the larvae of shoal- water benthic invertebrate species over long distances by ocean currents. Pp. 7-28. In Crisp, D. J. (ed.), Fourth European Marine Biology Symposium. Cambridge University Press; Cambridge.

SCHELTEMA, R. S., AND I. P. WILLIAMS. 1983. Long-distance dispersal of planktonic larvae and the biogeography and evolution of some Polynesian and western Pacific mollusks. Bulletin of Marine Science 33:545-565.

SMITH, J. T. 1970. Taxonomy, distribution and phylogeny of the cymatiid gastropods Argobuccinum, Fusitriton, Mediargo, and Priene. Bulletins of American Paleontology 56(254):443-573.

SOOT-RYEN, T. 1955. A report on the family Mytilidae. Allan Hancock Pacific Expeditions 20:1-175.

SOOT-RYEN, T. 1959. Reports of the Lund University Chile Ex- pedition 1948-49.35. Pelecypoda. Lunds Universitets Arsskrift, N.F. Avd. 2. Bd 55. 6:1-86.

SOUSA, W. P. 1984. The role of disturbance in natural communities. Annual Review of Ecology and Systematics 15:353- 391.

SPRINGER, V. G. 1982. Pacific plate biogeography, with special reference to shorefishes. Smithsonian Contributions to Zool- ogy 367:1-167.

STANLEY, E. M. 1981. Biogeography and evolution of "bipolar"

Radiolaria. Ph.D. Dissertation, Ecology. University of Califor- nia; Davis.

STEINMANN, G. 1896. Das Auftreten des Tertiars im nordlichen Chile. Pp. 531-547. In M6ricke, W., and G. Steinmann (eds.), Die Tertiairbildungen des nbrdlichen Chile und ihre Fauna. Neue Jahrbuch fur Mineralogie, Geologie und Palaontologie 10.

STEBHENSON, T. A., AND A. STEPHENSON. 1972. Life between Tidemarks on Rocky Shores. W. H. Freeman; San Francisco.

SVERDRUP, H. U., M. W. JOHNSON, AND R. H. FLEMING. 1942. The Oceans. Prentice-Hall; Englewood Cliffs.

THtEL, H. 1885. Report on the Holothuroidea. Part II. Voyage of the H.M.S. Challenger. Zoology 14:1-290.

TRENHAILE, A. S. 1987. The geomorphology of rock coasts. Clar- endon Press; New York.

UNDERWOOD, A. J. 1979. The ecology of intertidal gastropods. Advances in Marine Biology 16:111-210.

UNDERWOOD, A. J., AND E. J. DENLEY. 1984. Paradigms, expla- nations and generalizations in models for the structure of intertidal communities on rocky shores. Pp. 151-180. In Strong, D. R., Jr., D. Simberloff, L. G. Abele, and A. B. Thistle (eds.), Ecological Communities: Conceptual Issues and the Evidence. Princeton University Press; Princeton, New Jersey.

VAIL, P. R., AND J. HARDENBOL. 1979. Sea-level changes during the Tertiary. Oceanus 22:71-79.

VALENTINE, J. W. 1955. Upwelling and thermally anomalous Pacific coast Pleistocene molluscan faunas. American Journal of Science 253:462-474.

VALENTINE, J. W. 1961. Paleoecologic molluscan geography of the California Pleistocene. University of California Publica- tions in Geological Sciences 34:309-442.

VERMEIJ, G. J. 1978. Biogeography and adaptation. Harvard Uni- versity Press; Cambridge, Massachusetts.

VERMEIJ, G. J. 1987. Evolution and escalation. An ecological history of life. Princeton University Press; Princeton.

VERMEIJ, G. J. 1991. Anatomy of an invasion: the trans-Arctic interchange. Paleobiology 17:000-000.

VERMEIJ, G. J., A. R. PALMER, AND D. R. LINDBERG. 1990. Range limits and dispersal of molluscs in the Aleutian Islands, Alaska. Veliger 33(4):346-354.

VOKES, E. H. 1988. Muricidae (Mollusca: Gastropoda) of the Esmeraldas Beds, northwestern Ecaudor. Tulane Studies in Ge- ology and Paleontology 21(1):1-50.

WARHEIT, K. I., AND D. R. LINDBERG. 1988. Interactions between seabirds and marine mammals through time: interference competition at breeding sites. Pp. 292-328. In Burger, Jr. (ed.), Seabirds and Other Marine Vertebrates: Commensalism, Com- petition, and Predation. Columbia University Press; New York.

WEAVER, A. J. 1990. Ocean currents and climate. Nature 347: 432.

WEBB, S. D. 1985. Late Cenozoic mammal dispersals between the Americas. Pp. 49-85. In Stehli, F. G., and S. D. Webb (eds.), The Great American Biotic Interchange. Plenum Press; New York.

WHITE, B. N. 1986. The isthmian link, antitropicality and Amer- ican biogeography: distributional history of the Atherinopsi- nae (Pisces: Atherinidae). Systematic Zoology 35:176-196.

WILEY, E. 0. 1981. Phylogenetics. John Wiley and Sons; New York.

WILLIAMS, G. C., AND T. M. GOSLINER. 1979. Two new species of nudibranchiate molluscs from the west coast of North Amer- ica, with a synonymy in the family Cuthonidae. Zoological Journal of the Linnean Society 67:203-223.

Wu, S. K. 1985. The genus Acanthina (Gastropoda: Muricacea) in west America. Special Publication of the Mukaishima Ma- rine Biological Station 1985:45-66.

ZINSMEISTER, W. J. 1977. The formation of the West Antarctic ice sheet and its effect on the Miocene molluscan faunas of southern and central Chile. Abstracts with Programs, Annual Meeting, Geological Society of America 6:1240-1241.

marine biotic interchange between the northern and southern hemispheres

Documents