Metacommunity theories, which consider communities as interacting species assemblages connected by dispersal, differ in their assumptions about the importance of interspecific adaptations and environmental heterogeneity as controls of assemblage com- position. I assess the relative importance of regional (dispersal) and local (abiotic and biotic environmental variation) processes in explaining the structure of a freshwater pond meta- community. Results did not support the hypothesis that dispersal was limited by interpatch distance. Instead, community diversity, composition, and trophic structure were best ex- plained by local environmental variation associated with pond permanence. Many taxa were restricted either to temporary or semipermanent ponds, an outcome that suggests species trade off adaptations to disturbance with those to biotic interactions (species-sorting model) and that refutes the neutral model of interspecific equivalence. However, evidence for high dispersal rates, low-fitness habitats, and high temporal environmental variability indicated that interpatch dispersal also may influence local dynamics through mass effects. These results suggest that integrating the species-sorting and mass-effect niche assembly frame- works will provide a necessary step in the successful application of metacommunity theory.
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