US Hydrologic Classification Applied to Fish Traits: A Framework for Developing Flow-Ecology Hypotheses

Hydrologic classifications provide a template to describe ecological patterns, generalize hydrologic responses to disturbance, and organize management objectives.  We developed two updated hydrologic classifications for the continental US using two streamflow datasets of varying reference standards.  We also developed associations between each hydrologic classification and fish traits in order to form a template for generating flow-ecology hypotheses.  Including more streamflow gages increased the regional hydrologic distinctiveness and ecological predictive capacity of classes at the expense of decreasing the natural flow standards (i.e. reference quality). We observed tradeoffs in adaptive strategies for fish (reproductive and life history traits) across a spectrum of stable, perennial flow to unstable intermittent flow.  We also developed linkages between the uniqueness of hydrologic character and ecological distinction among classes, which may translate into predictions between losses in hydrologic uniqueness and ecological community response.  Ultimately, our results support the presumption that stream classes can provide an ecologically relevant context for developing environmental flow standards.