Cumulative Heat Stress in Fluctuating Temperatures and Implications for the Distribution of Freshwater Fish

Predicting how rising temperatures will impact different species and communities is imperative and increasingly urgent with ongoing global warming. Here, we describe how thermal-death time curves obtained in the laboratory can be combined with an envelope model to predict the mortality of freshwater fish under field conditions and their distribution limits. We analyze the heat tolerance and distribution of 22 fish species distributed across North America and demonstrate that high temperatures imposed a distribution boundary for 11 of them, employing a null model. Importantly, predicted thermal boundaries closely match the warmest suitable locality of the envelope model. Simulated warming suggests that the distribution of fish species with lower heat tolerances will be disproportionately affected by rising temperatures, and the rate of local extinctions will be higher across fish communities in warmer localities. Ultimately, our analyses illustrate how physiological information can be combined with distribution models to forecast how warming temperatures are expected to impact different species and ecological communities.