Three Competing Models for Predicting the Size of Species Pools: A Test Using Eastern North American Wetlands

With growing emphasis on protecting biodiversity, there is an increasing need for models which can predict the size of species pools in different habitats. Three models make predictions of how the species pool should change along environmental gradients. First, the productivity model predicts that the largest species pools will occur at high productivity (or at high biomass in herbaceous systems). Next, the species pool model predicts that the largest species pools will occur at the same biomass level as highest alpha diversity (the number of species in a small sample of uniform habitat). Finally, centrifugal organization predicts that species pools will be largest where biomass is low. We tested the three models to determine which was most appropriate using biomass/species composition data from 33 eastern North American wetlands. The resulting 640 quadrats produced a pattern of pool size consistent with the species pool model. Both alpha diversity and the species pool were maximum at intermediate biomass levels. This suggests that (1) the processes of stress tolerance, disturbance tolerance, and competition that are associated with changes in alpha diversity may also influence the species pool, and (2) the more easily measured alpha diversity values can be used to predict where large species pools might occur.