Characterizing fish community diversity across Virginia landscapes: Prerequisite for conservation

The number of community types occurring within landscapes is an important, but often unprotected, component of biological diversity. Generally applica ble protocols for characterizing community diversity need to be developed t o facilitate conservation. We used several multivariate techniques to analy ze geographic variation in the composition of fish communities in Virginia streams. We examined relationships between community composition and six la ndscape variables: drainage basin, physiography, stream order, elevation, c hannel slope, and map coordinates. We compared patterns at two scales (stat ewide and subdrainage-specific to assess sensitivity of community classific ation to spatial scale. We also compared patterns based on characterizing c ommunities by species composition vs. ecological composition. All landscape variables explained significant proportions of the variance in community c omposition. Statewide, they explained 32% of the variance in species compos ition and 48% of the variance in ecological composition. Typical communitie s in each drainage or physiography were statistically distinctive. Communit ies in different combinations of drainage, physiography, and stream size we re even more distinctive, but composition was strongly spatially autocorrel ated. Ecological similarity and species similarity of community pairs were strongly related, but replacement by ecologically similar species was commo n among drainage-physiography combinations. Landscape variables explained s ignificant proportions of variance in community composition within selected subdrainages, but proportions were less than at the statewide scale, and t he explanatory power of individual variables varied considerably among subd rainages. Community variation within subdrainages appeared to be much more closely related to environmental variation than to replacement among ecolog ically similar species. Our results suggest that taxonomic and ecological characterizations of comm unity composition are complementary; both are useful in a conservation cont ext. Landscape features such as drainage, physiography, and water body size generally may provide a basis for assessing aquatic community diversity, e specially in regions where the biota is poorly known. Systematic conservati on of community types would be a major advance relative to most current con servation programs, which typically focus narrowly on populations of imperi led species. More effective conservation of aquatic biodiversity will requi re new approaches that recognize the value of both species and assemblages, and that emphasize protection of key landscape-scale processes.