Scales of Dispersal and the Biogeography of Marine Predator-Prey Interactions
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vol. 171, no. 3 the american naturalist march 2008 ൴ Scales of Dispersal and the Biogeography of Marine Predator-Prey Interactions Evie A. Wieters,1,* Steven D. Gaines,2,3,† Sergio A. Navarrete,1,‡ Carol A. Blanchette,2,§ and Bruce A. Menge4,k 1. Estacio´n Costera de Investigaciones Marinas and Center for Keywords: dispersal scale, predator-prey population dynamics, mod- Advanced Studies in Ecology and Biodiversity, Las Cruces, els, biogeography, macroecology, marine. Pontificia Universidad Cato´lica de Chile, Casilla 114-D, Santiago, CP 6513677, Chile; 2. Marine Science Institute, University of California, Santa Species vary enormously in their average dispersal poten- Barbara, California 93106; tial. Some never venture far from their natal site; others 3. Department of Ecology, Evolution, and Marine Biology, regularly move on global scales. Large interspecific vari- University of California, Santa Barbara, California 93106; ation in dispersal distances among coexisting species is 4. Department of Zoology, Oregon State University, Corvallis, Oregon 97331 common in all ecosystems, both among species within trophic levels as well as between trophic levels (Kinlan and Submitted November 27, 2006; Accepted October 15, 2007; Gaines 2003). Dispersal of individuals determines the scale Electronically published January 25, 2008 at which species interact with the physical environment, the nature and consequences of the interaction with other Online enhancements: appendixes. species, the way in which they respond to perturbations, and ultimately the selective forces and rates to evolve, speciate, or become extinct. Consequently, many theoret- ical models have explored the consequences of varying abstract: Striking differences in the dispersal of coexisting species dispersal rates for individual species as well as species in- have fascinated marine ecologists for decades. Despite widespread teractions (e.g., Levin 1974; Caswell 1978; Roughgarden attention to the impact of dispersal on individual species dynamics, and Iwasa 1986; Pulliam 1988; Gaines and Lafferty 1995; its role in species interactions has received comparatively little at- Loreau and Mouquet 1999; Chesson 2000; Amarasekare tention. Here, we approach the issue by combining analyses of simple and Nisbet 2001; Lockwood et al. 2002; Amarasekare 2003; heuristic predator-prey models with different dispersal patterns and Snyder and Chesson 2003). However, because of logistic data from several predator-prey systems from the Pacific coasts of difficulties, most predictions from models that include dif- North and South America. In agreement with model predictions, differences in predator dispersal generated characteristic biogeo- ferential dispersal of interacting species remain largely graphic patterns. Predators lacking pelagic larvae tracked geographic untested, except in controlled experimental arenas and in- variation in prey recruitment but not prey abundance. Prey recruit- volving species with comparatively short dispersal dis- ment rate alone explained more than 80% of the biogeographic var- tances (e.g., Gonzalez et al. 1998; Shurin 2001; see Leibold iation in predator abundance. In contrast, predators with broad- et al. 2004 for review). casting larvae were uncorrelated with prey recruitment or adult prey Contrasting dispersal capabilities among coexisting spe- abundance. Our findings reconcile perplexing results from previous cies is especially apparent in marine habitats, where var- studies and suggest that simple models can capture some of the iation in the mode of larval development alone imposes complexity of life-history diversity in marine communities. average dispersal distances that vary by many orders of magnitude (Kinlan and Gaines 2003; Shanks et al. 2003; * E-mail: [email protected]. Levin 2006). At one end of the spectrum lie many sea- † E-mail: [email protected]. weeds, some invertebrates, and a few fish, which produce ‡ E-mail: [email protected]. young that can develop within meters of their parents. § E-mail: [email protected]. These populations are demographically closed on relatively k E-mail: [email protected]. small spatial scales, since the dynamics at a given location Am. Nat. 2008. Vol. 171, pp. 405–417. ᭧ 2008 by The University of Chicago. are likely to be governed by local processes affecting birth 0003-0147/2008/17103-42241$15.00. All rights reserved. and mortality rates. At the other end of the spectrum are DOI: 10.1086/527492 many marine invertebrates and nearly all fish, which pro- 406 The American Naturalist duce young that develop in the plankton for weeks to Material and Methods months and can be dispersed widely by ocean currents Field Data (Scheltema 1986; Caley et al. 1996). The longer the larval development, the larger the scales of dispersal (Kinlan and Examining the relationship between predators and prey Gaines 2003; Shanks et al. 2003; Siegel et al. 2003; Levin requires information on geographic patterns of population 2006), and the more a local population becomes demo- abundances and recruitment rates of young. Moreover, graphically open with its growth decoupled from the local temporal variation in prey recruitment makes it necessary production of young (Gaines and Roughgarden 1985; to integrate information over relatively long periods of Roughgarden et al. 1985). Existing theoretical explorations time with respect to the biological response variable ex- (e.g., Iwasa and Roughgarden 1986; Kuris and Lafferty amined (i.e., predator population abundance). We com- 1992; Gaines and Lafferty 1995; Connolly and Roughgar- piled such data sets for several predator-prey combinations den 1999b; Vela´zquez et al. 2005) suggest that this kind from two regions of the world, the Pacific coast in North of variability in dispersal distances can greatly alter the America and the central coast of Chile in South America. dynamics and stability of species interactions. Considering We used essentially the same field methods in both hemi- that dispersal and connectivity in populations of marine spheres, facilitating comparisons across different predator- species can occur over scales of tens to hundreds of ki- prey systems. Moreover, comparisons between predators lometers, it is not surprising that empirical information of the same taxa (e.g., muricid whelks) but with contrast- to evaluate these model predictions is largely absent. Here, ing life histories allowed more rigorous examination of the we begin this exploration by examining several intertidal influence of dispersal scale. predator-prey interactions where the interacting species All sites in this study were open-coast, wave-exposed have different dispersal scales. rocky shores (fig. B1 in the online edition of the American Most studies of predator-prey interactions have exam- Naturalist). Within a region, among-site variability in ined dynamics at a single location (but see Dethier and physical conditions was minimized by selecting, wherever Duggins 1988; Menge et al. 1994, 2004; Navarrete et al. possible, rocky benches of similar geomorphology, slope, 2005; Navarrete and Manzur 2008). Dispersal, however, and orientation to prevailing swell. The greatest hetero- geneity among sites occurred along the central California links populations across sites. Hence, we implemented a coast, where coastline orientation and wave exposure unique set of empirical studies that focus on patterns changes sharply about Point Conception. across numerous sites within biogeographically widespread At 20 rocky intertidal sites spanning 2,100 km from predator-prey systems found along the temperate west central California to Oregon (fig. B1), we estimated the coasts of North and South America. Although a wide range abundance of predatory whelks and the sea star Pisaster of dispersal patterns may be found within marine pred- ochraceus, the main benthic predators in this system (Na- ator-prey systems, we initially concentrate only on varia- varrete and Menge 1996; Menge et al. 2004). In Oregon, tion in the dispersal scale of predators that prey on in- common whelk species included Nucella canaliculata and vertebrates with pelagically dispersed larvae and sessile Nucella ostrina, whereas Nucella emarginata and Acan- adults (e.g., mussels, barnacles), since these commonly thinucella spirata were prevalent in central California. dominate space and are by far the most important inver- These whelk species are direct developers that lay benthic tebrate component of the basal trophic level in most ben- egg capsules from which small juveniles crawl away (e.g., thic marine communities worldwide. We consider the most Spight 1974). In contrast, sea stars have broadly dispersed ubiquitous predator-prey species in each biogeographic pelagic larvae that spend anywhere between 75 and 230 region, including two classes of predators: those that pro- days in the water column (Strathmann 1987). Sea stars duce young locally versus those that broadcast larvae into and whelks feed on mussels (Mytilus californianus, Mytilus the plankton. As a first step toward incorporating life his- galloprovinciallis, and Mytilus trossulus) and barnacles tory and dispersal in predator-prey models for marine (mostly Balanus glandula and Chthamalus spp. but also organisms, and since we do not have information on actual Semibalanus cariosus and Pollicipes polymerus). Genetically dispersal distances of these species, we used simple models fixed geographic variation in prey preferences has been of local interactive populations in which species