Abstract
Increased dispersal of individuals among discrete habitat patches should increase the average number of species present in each local habitat patch. However, experimental studies have found variable effects of dispersal on local species richness. Priority effects, predators, and habitat heterogeneity have been proposed as mechanisms that limit the effect of dispersal on species richness. However, the size of a habitat patch could affect how dispersal regulates the number of species able to persist. We investigated whether habitat size interacted with dispersal rate to affect the number of species present in local habitats. We hypothesized that increased dispersal rates would positively affect local species richness more in small habitats than in large habitats, because rare species would be protected from demographic extinction. To test the interaction between dispersal rate and habitat size, we factorially manipulated the size of experimental ponds and dispersal rates, using a model community of freshwater zooplankton. We found that high‐dispersal rates enhanced local species richness in small experimental ponds, but had no effect in large experimental ponds. Our results suggest that there is a trade‐off between patch connectivity (a mediator of dispersal rates) and patch size, providing context for understanding the variability observed in dispersal effects among natural communities, as well as for developing conservation and management plans in an increasingly fragmented world.
Highlights
Over the past several decades, community ecology has shifted from a focus on local factors such as abiotic filters and species interactions, to one that recognizes the interplay between local and regional factors, such as dispersal (e.g., Leibold et al, 2004; Logue, Mouquet, Peter, & Hillebrand, 2011)
In addition to understanding variation in richness among habitats that naturally vary in their isolation, interest in the influence of habitat isolation on dispersal limitation has been boosted by global habitat loss and fragmentation, leading to species extinctions and reduced biodiversity (Damschen et al, 2008; Gilbert, Gonzalez, & Evans-Freke, 1998; Gonzalez & Chaneton, 2002; Haddad et al, 2015; Helm, Hanski, & Pärtel, 2006)
In small, freshwater ponds, some studies have shown that increased dispersal rates have a negligible influence on local species richness (e.g., Forbes & Chase, 2002; Shurin, 2000) while others have shown strong effects (Cottenie & De Meester, 2004; Howeth & Leibold, 2010; McCauley, 2006)
Summary
Over the past several decades, community ecology has shifted from a focus on local factors such as abiotic filters and species interactions, to one that recognizes the interplay between local and regional factors, such as dispersal (e.g., Leibold et al, 2004; Logue, Mouquet, Peter, & Hillebrand, 2011). Species may not disperse randomly or may be dispersal limited (e.g., Jacquemyn, Butaye, & Hermy, 2001) In such cases, landscape factors including increased habitat heterogeneity, habitat patch proximity, or trophic interactions would affect the relationship between patch size and local species richness within a metacommunity (Scheffer et al, 2006). If the available niche space does not depend on habitat size, and competitive species are not dispersal limited, we would expect to find that higher rates of dispersal would increase species richness more in small mesocosms than in large. In this case, we expect that rescue effects would be an important mechanism affecting the number of species in small mesocosms. These results are consistent with predictions from the Equilibrium Theory of Island Biogeography model
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