Does hydrology constrain the structure of fish assemblages in French streams?: Regional scale analysis

My goal was to test whether fish-hydrology relationships detected at the local scale (within sites, between years) could be transferred to the regional scale (between sites), i.e. whether long-term flow patterns could explain differences in average assemblage structures between sites. Species guild proportions, assemblage diversity measures, and species trait proportions were significantly predictable from geomorphic, hydraulic, and hydrological variables (similar to 11% < r(2) < similar to 96%). Once the effects due to the longitudinal gradient and local habitat conditions were controlled, the average magnitude of flow regimes during the spawning or growth periods significantly constrained 13 out of 16 tested biological variables. This suggests that flow regime delineates a physical habitat template for lotic systems, within which species adapt by physiological, behavioural, or morphological responses. However, the trends of relationships observed between sites sometimes differed from those revealed within sites, suggesting that the effect of a given physical variable is scale-dependent.