Validating Hydrologic Classifications Schemes for the Contiguous US Using Functional and Taxonomic Composition of Stream Fish Communities

Stream classifications based on hydrologic regimes are frequently used to characterize spatial variation in stream habitat; however their utility as prioritization tools for biodiversity conservation requires that hydrologic classes capture the spatial variation in taxonomic and functional composition of aquatic communities. We compiled fish community samples and summarized functional and taxonomic composition from 97 streams throughout the contiguous United States. Hydrologic regimes were classified using recently-developed classification schemes containing 2 to 30 hydrologic classes. Permutational MANOVAs were used to quantify the relationship between hydrologic class membership and community composition. Hydrologic classes explained 23 to 41% of the variation in community composition. Classification schemes with more hydrologic classes explained more variation, indicating a tradeoff between the simplicity of a classification scheme and its ability to resolve spatial variation in community composition. Classification schemes did not differ in their ability to describe variation in functional versus taxonomic aspects of the community. Refined classification schemes that holistically reflect biodiversity patterns will be used with geospatial data describing existing and potential future hydropower facilities to prioritize the preservation of unique stream types with the goal of maximizing the protection of biodiversity.