The relationship between dispersal ability and geographic range size

Abstract

There are a variety of proposed evolutionary and ecological explanations for why some species have more extensive geographical ranges than others. One of the most common explanations is variation in speciesÕ dispersal ability. However, the purported relationship between dispersal distance and range size has been subjected to few theoretical investigations, and empirical tests reach conflicting conclusions. We attempt to reconcile the equivocal results of previous studies by reviewing and synthesizing quantitative dispersal data, examining the relationship between average dispersal ability and range size for different spatial scales, regions and taxonomic groups. We use extensive data from marine taxa whose average dispersal varies by seven orders of magnitude. Our results suggest dispersal is not a general determinant of range size, but can play an important role in some circumstances. We also review the mechanistic theories proposed to explain a positive relationship between range size and dispersal and explore their underlying rationales and supporting or refuting evidence. Despite numerous studies assuming a priori that dispersal influences range size, this is the first comprehensive conceptual evaluation of these ideas. Overall, our results indicate that although dispersal can be an important process moderating speciesÕ distributions, increased attention should be paid to other processes responsible for range size variation.Keywords Biogeography, colonization, dispersal, geographical distribution, marine, pelagic larval duration, range size, selection, speciation. Why do some species have larger geographical ranges than others? This is a fundamental, yet largely unanswered, question in ecology and biogeography. Even closely related species can have dramatically different range sizes (Brown et al. 1996), and a variety of evolutionary and ecological explanations for range size variation have been suggested, including niche breadth or environmental tolerance, body size, population abundance, latitude, environmental variability, colonization and extinction dynamics, and dispersal ability (Stevens 1989;Brown et al. 1996;Gaston 1996Gaston , 2003. However, tests of many of these hypothetical causes are limited, and none has emerged as a universal driver of the extent of speciesÕ geographical distributions.An organism's ability to disperse is one of the more commonly cited potential determinants of a speciesÕ range (Hanski et al. 1993;Brown et al. 1996;Gaston 1996Gaston , 2003. Dispersal ability is invoked as an explanation for range size variation in both terrestrial and marine systems and for a wide range of taxa, including insects (Juliano 1983;Gutierrez & Menendez 1997;Malmqvist 2000;Brandle et al. 2002), plants (Oakwood et al. 1993Edwards & Westoby 1996;Thompson et al. 1999;Clarke et al. 2001;Lloyd et al. 2003;Lowry & Lester 2006), fish (Wellington & Victor 1989;Goodwin et al. 2005;Lester & Ruttenberg 2005;Mora & Robertson 2005) and mollusks (Hansen 1980;Perron & Kohn 1985;Jablonski 1986;Scheltema 1989;...

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