Evaluating and Improving Current Metapopulation Theory for Community and Species-level Models

Ecological models that attempt to unite biodiversity and biogeography concepts have been used to describe and predict the distribution and abundance of species. Mechanistic ecological models theorize that demographic and distributional dynamics affect the success and persistence of the species making up the community. The community-level metapopulation model is one such model and assumes that the species at a particular island are determined by species-specific extinction and colonization rates which vary with island area and isolation from the mainland. In this dissertation, I tested the extent of the model’s ability to capture the underlying mechanisms shaping the community and compare that to another mechanistic model and a null model. I used simulated island-mainland systems with varying number of islands, island sizes, and distances to mainland along with mainland communities with varying numbers of species and densities. I found that there was a limited range of system and community variables where the community-level metapopulation model could accurately describe the species richness on islands created using metapopulation dynamics better than the alternative models. Using these guidelines for system and community structure, I empirically tested evidence for metapopulation dynamics structuring small mammal, tree, and moth communities within an island-mainland system that fit the requirements. The community-level metapopulation model was not found to be better than a null model for describing the species richness patterns of all three functional taxa. The moth taxon was best described by the diversity of host plant species. Lastly, the descriptive ability of the community-level metapopulation model is dependent upon the accuracy of the underlying single-species model. An assumption of the metapopulation model that is often violated is the assumption of a constant density-area relationship. I incorporate a method to correct for variable density-area relationships within the single-species metapopulation model estimate of extinction risk. I then compared estimates of extinction risk with and without accounting for variable density-area relationships on empirical data: the density of mammals, trees, and moths in an island-mainland system. I found 63% of species across the three taxa violated the assumption of a constant density-area relationship. I found variability in the relationship between density and area. Estimates of extinction risk were inflated for most species before accounting for a variable density-area relationship on smaller islands.