Historical and Ecological Factors in the Evolution, Adaptive Radiation, and Biogeography of Freshwater Mollusks

SYNOPSIS. There are some 36 families that are wholly freshwater or with representative species in freshwater. There are virtually no phylogenetic analyses for these families. Zoogeographic analyses of freshwater molluscan faunas are hindered by a lack of significant systematic studies of these faunas. Such studies are essential if one hopes to develop hypotheses about phylogeny or biogeography. It is clear from a phylogenetic analysis of the Pomatiopsidae that phylogenetic, vicariance, dispersal, and ecological factors all have significant effects on the patterns of distribution of this family. At one stage in history vicariance may be a dominant factor while during another stage of history, dispersal may be a dominant factor. At every stage, ecological considerations are necessary to understand the phenotypes seen and the spatial relationships among taxa. In examining the distribution patterns of dominant freshwater families with regard to their biological, ecological, and overall phylogenetic relationships it is evident that ecology plays a major role along with dispersal and vicariance. Clearly a synthesis is needed in biogeographical studies that incorporates vicariance dispersal, ecology, and geology-paleontology.