Fish assemblages respond to altered flow regimes via ecological filtering of life history strategies

Mims, M.C., and J.D. Olden. 2013. Fish assemblages respond to altered flow regimes via ecological filtering of life history strategies. Freshwater Biology 58:50-62.

In riverine ecosystems, streamflow determines the physical template upon which the life history strategies of biota are forged. Human freshwater needs and activities have resulted in widespread alteration of the variability, predictability and timing of streamflow, and anticipating the biotic consequences of anthropogenic streamflow alteration is critical for successful environmental flow management. In this study, we examined relationships between dam characteristics, metrics of flow alteration and fish functional community composition according to life history strategies by coupling stream flow records and fish survey data in paired flow-regulated and free-flowing rivers across the conterminous United States. Our study demonstrated that river regulation by large dams has significant hydrological and biological consequences across the United States. We showed that on ecological time scales (i.e. the order of years to decades), dams are effectively changing the functional composition of communities that have established over millennia. Furthermore, the changes are directional and indicate a filtering by dams for some life histories (equilibrium strategists) and against other life histories (opportunists). Finally, our study highlights that dependence upon long-term flow records and availability of biotic
surveys extracted from national survey efforts limit our ability to guide environmental flow standards particularly in data-poor regions.