How are regional species pools used in community ecology?
Ecologists have long recognized that the composition and richness of local communities are influenced by biogeographic and evolutionary processes acting at large spatial and temporal scales. Considering the regional species pool can make the influences of these processes tractable in ecological analyses. Broadly, a regional species pool is defined as the set of all species available to colonize a focal site. Assessing variation in the size and composition of regional species pools and determining their relationship to the composition of local communities—including their richness, phylogenetic/functional trait structure, and spatial variation (beta diversity)—is a way to include the potential influence of large-scale processes into analyses of community assembly. The goal of this talk is to discuss the conceptual and practical issues that should be considered when defining regional species pools and when exploring their influence on community structure.
Both theory and evidence show that pool influences are greatest when local communities are not strongly and predictably structured by species interactions (e.g., under frequent disturbance or if many species are rare). Practical and conceptual issues to consider when delineating species pools include choosing an appropriate spatial scale, whether to account for environmental filtering, whether to include the species within a fixed geographic area versus those whose geographic ranges overlap with a site, or whether to use databases or geographic data sources. Each issue is discussed in the context of 63 studies using the species pool approach. The studies show that species pools can be used to test for local vs. regional influences on local diversity, to test for regional influences on beta diversity, to test for regional influences on phylogenetic structure, and to test for regional influences on the outcome of experiments. Future studies must compare pool characteristics with community structure across multiple regions for a more complete understanding of community assembly.