Aim We evaluated variation in fish assemblages on the basis of taxonomic composition and functional groups based on Pleistocene glacial boundaries in the Ohio River basin. We tested for the influence of habitat and hydrology on fish assemblage variation.
Location Ohio River basin of North America, including the states of Ohio, Indiana and Illinois.
Methods Fish collection sites were identified as Wisconsinan, pre-Wisconsinan or unglaciated regions. Multivariate analyses, multi-response permutation procedures, discriminant analysis and indicator species analyses were used to test whether taxonomic and functional assemblages were distinct among regions with varying glacial histories. Principal components analysis was used to identify habitat and water quality, as well as hydrological gradients that could be discerned by glacial region.
Results We identified significant differences in both taxonomic and functional fish assemblage structure and habitat variation among regions that had different glaciation histories. The largest differences in taxonomic and functionally based fish communities were for unglaciated and pre-Wisconsinan regions, while unglaciated and Wisconsinan regions were most similar. We correctly classified study regions in 71% and 60% of sites using taxonomy and functional analyses, respectively. Wisconsinan sites were characterized by Cyprinidae and Catostomidae assemblages with high abundances of tolerant fishes that tended to occur in habitats with reduced current velocity. Pre-Wisconsinan sites were characterized by Cyprinidae, Catostomidae, Centrarchidae and Percidae families with increased abundances of intolerant fishes that tended to occur in habitats with coarser substrates and increased water velocity in streams of varying size. Unglaciated sites were characterized by Cyprinidae and Percidae families and were not closely associated with any habitat-based functional group. Habitat in the unglaciated and pre-Wisconsinan sites was significantly different from that in the Wisconsinan sites, which were characterized by increased channel structure and reduced stream size.
Main conclusions Pleistocene glaciation events formed a lasting template of predictable regional differences in stream habitat and in the corresponding taxonomic and functional fish assemblage structures. While many factors impact the distribution of fishes, these results suggest that historical influences such as glaciation may be used to further explain the underlying mechanisms of spatial variation in fish assemblages.