FACTORS AFFECTING THE OCCURRENCE AND STRUCTURE OF FISH ASSEMBLAGES INISOLATED WETLANDS OF THE UPPER COASTAL-PLAIN, USA

To test a model of fish assemblage structure in isolated wetlands of t he Atlantic Coastal Plain, we related the presence or absence of fishe s in individual wetlands and variation in assemblage structure to envi ronmental conditions within wetlands and to location in relation to pe rmanent aquatic habitats. Fishes were limited to wetlands that dried i nfrequently, were relatively close to intermittent aquatic habitats, a nd had little elevation difference between the wetland and its nearest permanent aquatic habitat. Comparison of variation in assemblage stru cture among wetlands to null hypotheses of randomness suggested that b iological interactions played a minor role in structuring these assemb lages. We found no correlation between assemblage structure and wetlan d environment. Variation in assemblage structure was correlated with t he geographic position of wetlands. Wetlands located in the upper port ions of drainage basins were dominated by Lepomis marginatus and Erimy zon sucetta while wetlands located in downstream portions of drainage basins were dominated by Acantharchus pomotis and Gambusia holbrooki. Our results are consistent with a model of fish assemblage structure i n which wetland drying frequency and connectivity determine the presen ce or absence of fishes, and differences in colonizing rates and the r elative abundance of species in source pools influence variation among wetlands with fishes.