Regional patterns of mussel species distributions in North American rivers

North American freshwater mussels are a highly threatened group with half of the fauna already federally listed as threatened or endangered, candidates for listing, or believed extinct. Using data From 16 river systems, I examined distributional attributes of mussel species to pain insight into the importance of regional-scale processes vs local-scale processes to species distribution patterns. There was no evidence of density compensation or saturation, which would have indirectly indicated that competition was important in structuring mussel communities. Rather, there was a positive correlation between summed species densities and regional richness. indicating that regional forces may be strongly contributing to community structure. Incidence, abundance and nestedness patterns all indicated a hierarchical niche structure for these mussel assemblages. I hypothesize that these hierarchical patterns may be the result of differences in colonization potentials among mussel species as a result of different fish-host requirements among mussels, and of the abundance and distribution of those host fishes.