Factors affecting the occurrence and structure of fish assemblages in isolated wetlands of the upper coastal plain, U.S.A.

To test a model of fish assemblage structure in isolated wetlands of the Atlantic Coastal Plain, we related the presence or absence of fishes in individual wetlands and variation in assemblage structure to environmental conditions within wetlands and to location in relation to permanent aquatic habitats. Fishes were limited to wetlands that dried infrequently, were relatively close to intermittent aquatic habitats, and had little elevation difference between the wetland and its nearest permanent aquatic habitat. Comparison of variation in assemblage structure among wetlands to null hypotheses of randomness suggested that biological interactions played a minor role in structuring these assemblages. We found no correlation between assemblage structure and wetland environment. Variation in assemblage structure was correlated with the geographic position of wetlands. Wetlands located in the upper portions of drainage basins were dominated by Lepomis marginatus and Erimyzon sucettawhile wetlands located in downstream portions of drainage basins were dominated by Acantharchus pomotisand Gambusia holbrooki. Our results are consistent with a model of fish assemblage structure in which wetland drying frequency and connectivity determine the presence or absence of fishes, and differences in colonizing rates and the relative abundance of species in source pools influence variation among wetlands with fishes.