An Evaluation of the Influence of Fragmentation on Stream Fish Communities Using Spatially-Explicit Metapopulation Models

Stream fragmentation has been identified and one of the primary threats to stream-dwelling fish species in North America. In the Atlanta Metropolitan Area, growing human populations and the desire to minimize the effect of frequent droughts on water supplies has led to the demand for additional water supply reservoirs. Such reservoirs can fragment stream systems, potentially decreasing the persistence and resilience of stream fish communities.  We developed a landscape-scale approach to predict the effects of stream fragmentation and streamflow alteration on the distribution and persistence of fish communities within the Apalachicola, Chattahoochee, and Flint (ACF) river basins. The modeling approach integrates climate, geology, geomorphology, hydrology, and landscape characterizations. The ecological models simulate the dynamics of fish communities in individual stream segments using empirical estimates of meta-demographic rates (colonization, extinction, reproduction) and operate on a seasonal time step. These ecological models were linked to hydrologic models to predict the persistence of fish species under future scenarios of stream fragmentation due to reservoir construction. Simulations of increasing levels of fragmentation indicated that predicted fish species richness declined as fragmentation increased and suggested a presence of threshold level of fragmentation where the resilience of the fish community was lost. Estimates of the effects of fragmentation, however, varied substantially with assumptions regarding the colonization dynamics of fish populations.