Influences of local habitat and stream spatial position on fish assemblages in a dammed watershed, the Qingyi Stream, China

Identifying the underlying mechanisms that explain the spatial variation in stream fish assemblages is crucial for the protection of species diversity. The influences of local habitat and stream spatial position on fish assemblages were examined from first-order through third-order streams within a dammed watershed, the Qingyi Stream, China. Based on linear regression models, the most important environmental variables influencing fish species richness were water temperature and wetted width, but stream spatial position variables were less important. Using canonical correspondence analysis, five environmental variables were identified to significantly influence fish assemblages, including three habitats (elevation, substrate and water depth) and two spatial variables (C-link and Link). Our results suggest that, in a heavily dammed watershed, by blocking the migration routes of fishes, dams weaken the influence of stream spatial position on fish species richness. However, fish species compositions are significantly influenced by both local habitat environment and stream spatial position, which is perhaps owing to the distribution of fish species according to ecological requirements not related to spatial processes.