Dissecting fine-scale climate vulnerability for freshwater fish in Illinois: Overlap between climate exposure, warming tolerance and adaptive capacity

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Lucas K. Do and Lise C. Comte, School of Biological Sciences, Illinois State University, Normal, IL

Background/Question/Methods
Biological communities are expected to undergo substantial reassembly in response to climate change as species track their climatic niche through space. Yet, evidence suggests that some species may not be able to keep pace with rapidly changing climatic conditions, resulting in taxonomically and spatially varying patterns of climate vulnerability. This may be particularly consequential in freshwater ecosystems, where dispersal ability is constrained by the river network and where human-made fragmentation structures may impede redistribution. Here, we assessed climate vulnerability of freshwater fish communities at 1,042 sites throughout the state of Illinois accounting for (1) climate exposure as the predicted speed and direction of climate shifts (climate velocity) between the reference period 1981-2010 and the future period 2041-2070, (2) species sensitivity as the difference between critical thermal maximum and local summer water temperature (warming tolerance), and (3) species adaptive capacity as a combination of population dispersal ability estimated based on morphological traits and environmental factors (dispersal velocity) and degree of fragmentation by dams and roads (habitat permeability). We also tested whether methodological decisions such as choice of climate scenario used to characterize climate exposure (moderate versus high emissions) and choice of dispersal velocity estimate (mean versus maximum dispersal distance) lead to uncertainty in the assessment of future vulnerability.
Results/Conclusions
Our results suggest widespread climate vulnerability of fish communities in Illinois, driven by a combination of high sensitivity to temperature increases (low warming tolerance) and limited adaptive capacity (low dispersal ability and habitat permeability). Notably, we found that more than 72% of communities show a dispersal deficit, i.e. maximum dispersal velocities insufficient to keep pace with the projected rates of climate change, especially in low-order headwater streams. However, warming tolerances tend to be negatively correlated with dispersal ability, indicating that more sensitive communities are also better able to cope with predicted climate changes. Importantly, the vulnerability metrics developed were highly sensitive to the choice of moderate versus high emissions climate scenario for climate exposure, and mean versus maximum dispersal distance for adaptive capacity. These results highlight the need for greater consideration of spatial overlap among the different dimensions of vulnerability together with an assessment of their uncertainty to better inform climate change adaptive strategies in the future.