Warming Tolerances for 34 Species of Anurans Native to the Southeast United States

Identifying how close species are to their current upper thermal limits estimates species sensitivity to climate change (or the species ability to persist in place without changing). Process-based models like the NicheMapR mechanistic niche model (Kearney et al. 2019; https://doi.org/10.1111/ecog.04680) use a mass-balance approach to translate microclimate estimates into individual animal operative body temperatures based on biological traits. Using NicheMapR, we quantified 34 species' warming tolerance, or the difference between species critical thermal maximum and its modelled operative temperature, from 2011 to 2020 across approximately 18% of its range within the southeastern United States. Using available intraspecific trait values, we also investigated how intraspecific variation in preferred temperature and more or less sensitive traits suites affected our estimates of warming tolerance. Many species are already at their upper thermal limits during extreme high temperatures, with twenty species having negative minimum daily minimum warming tolerances in 25% of their modelled range, an average of 39.3% of modelled points below 0 during extreme temperatures, and an average minimum daily minimum warming tolerance of 1.2 degrees Celsius (range -5.0 to 10.5 degrees Celcius). Most species have some warming tolerance during the warmest quarter of the year (average 25th quartile of daily minimum warming tolerance = 9.1 degrees Celsius, range 0.8 to 15.5 degrees Celsius). Our investigation of how intraspecific trait variation affects model outputs revealed that variance in preferred temperature effects our estimates of sensitivity to seasonal and annual increases in warm temperature but not to extreme temperature events. Intraspecific models that included the most and least sensitive trait suites found congruent estimates of thermal sensitivity. All told, anuran species native to the Southeast United States vary in their thermal sensitivity, with some species already living close to their upper thermal limits.

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