The Appalachian Mountains in the southeastern United States is a hotspot for fish diversity, but little is known about interspecific variation in thermal biology or acute exposure to temperature extremes. Our goal was to (1) assess thermal habitat use and physiological tolerance, and (2) forecast distributional changes and warming tolerance of four endemic fishes (Notropis leuciodus, N. rubricroceus, Etheostoma rufilineatum, and E. chlorobranchium) that differ in elevational limits and represent the two most species-rich clades in the region. We used environmental niche modeling (ENM) to map distributions of these species in the Upper Tennessee River basin and we combined thermal tolerance experiments and simulations of extreme heat events at 35 stream reaches to assess potential for acute heat stress under contemporary and future climates.
Results/Conclusions
ENMs projected a decline in suitable habitat and an upslope shift for all species except the low-elevation darter, E. rufilineatum, which is projected to expand its range into high-elevation streams. Laboratory-measured thermal tolerances, ranging from 28.5 to 37.2°C, were driven largely by acclimation temperature rather than current elevation affinity. Extreme heat events never exceeded thermal tolerances under contemporary climate, but did at low elevations under future climates. Taken together, these results suggest that thermal optima drive contemporary elevational limits of the four species, whereas both optima and maxima will likely drive future elevational shifts. Integrating physiological and distributional information provided complementary insight into the drivers of contemporary elevational limits and warming-induced shifts in the future.