3 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 increasi ng need for models which can predict the size of species pools in diff erent habitats. Three models make predictions of how the species pool should change along environmental gradients. First, the productivity m odel predicts that the largest species pools will occur at high produc tivity (or at high biomass in herbaceous systems). Next, the species p ool model predicts that the largest species pools will occur at the sa me 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 t ested the three models to determine which was most appropriate using b iomass/species composition data from 33 eastern North American wetland s. The resulting 640 quadrats produced a pattern of pool size consiste nt with the species pool model. Both alpha diversity and the species p ool were maximum at intermediate biomass levels. This suggests that (1 ) the processes of stress tolerance, disturbance tolerance, and compet ition that are associated with changes in alpha diversity may also inf luence the species pool, and (2) the more easily measured alpha divers ity values can be used to predict where large species pools might occu r.