Impacts of climate and land use change on fish species distributions in the central United States

Species distribution models are useful tools that can be used to evaluate tradeoffs of management and conservation strategies under scenarios of environmental change. Modeling efforts for fish species have largely focused on cold-water, commercial, and recreationally-valued species, even though warm-water, non-game species have important roles in ecosystem services and processes. I developed species distribution models for fourteen warm-water fish species native to the Central United States and evaluated environmental drivers and predictive performance. I used an ensemble model approach produced by combining forecasts of five single-model techniques. Response plots and variable importance calculations were used to evaluate the influence of individual variables. The predictive performance of the ensemble models was assessed using area under the curve (AUC) of the receiver-operating characteristic plot. Ensemble model AUC values generally performed better than single-model types, suggesting ensemble models are more reliable and applicable for management purposes than single-models. Most models were influenced by a mix of climate, land use and geophysical variables; however, climate variables were the dominant environmental drivers across models. Next, I projected distribution responses of 14 warm-water fish species to climate and land use scenarios using the ensemble models combined with scenario analyses. I incorporated different time periods, greenhouse gas emissions scenarios, and general circulation models into the scenario analysis. I then tested the effect of climate change scenario and the incorporation of land use on range change. Although it has been hypothesized that warm-water fishes will generally benefit from future climate changes through range expansion, I found wide variability in range change across the species modeled. There was a significant effect of greenhouse gas scenario and year on overall range change for half of the species modeled. The incorporation of future land use projections into scenarios generally led to increased range expansion. I combined all scenarios into consensus projections to visualize range change projections across all scenarios. Some species expanded their range to the north and into higher elevations while other species were projected to lose significant portions of their range. For example, orangethroat darter (Etheostoma spectabile) is projected to gain between 30 to 90 percent new range and lose between 0 to 6 percent of its current range while bigmouth shiner (Hybopsis dorsalis) is projected to gain between 0 to 20 percent new range and lose 75 to 100 percent of its current range. Variability in climate change responses across warm-water species may be a result of ecological traits, such as range size and fecundity. The variability in warm-water species\u27 responses suggests management of these species can be informed through the use of species distribution modeling and scenario analysis