1. The vulnerability of species to climate change is jointly influenced by geographic phenotypic variation, acclimation, and behavioral thermoregulation. The importance of interactions between these factors, however, remains poorly understood.

2. We demonstrate how advances in mechanistic niche modelling can be used to integrate and assess the influence of these sources of uncertainty in forecasts of climate change impacts.

3. We explored geographic variation in thermal tolerance (i.e. maximum and minimum thermal limits) and its potential for acclimation in juvenile European common frogs (Rana temporaria) along elevational gradients. Further, we employed a mechanistic niche model (NicheMapR) to assess the relative contributions of phenotypic variation, acclimation and thermoregulation in determining the impacts of climate change on thermal safety margins and activity windows.

4. Our analyses revealed that high elevation populations had slightly wider tolerance ranges driven by increases in heat tolerance but lower potential for acclimation. Plausibly, wider thermal fluctuations at high elevations favor more tolerant but less plastic phenotypes, thus reducing the risk of encountering stressful temperatures during unpredictable extreme events. Biophysical models of thermal exposure indicated that observed phenotypic and plastic differences provide limited protection from changing climates. Indeed, the risk of reaching body temperatures beyond the species’ thermal tolerance range was similar across elevations. In contrast, the ability to seek cooler retreat sites through behavioral adjustments played an essential role in buffering populations from thermal extremes predicted under climate change. Predicted climate change also altered current activity windows, but high-elevation populations were predicted to remain more temporally constrained than lowland populations.

5. Our results demonstrate that elevational variation in thermal tolerances and acclimation capacity might be insufficient to buffer temperate amphibians from predicted climate change; instead, behavioral thermoregulation may be the only effective mechanism to avoid thermal stress under future climates.

This data package contains experimentally measured critical thermal limits of juvenile Rana temporaria from populations distributed across elevations. These data are presented in Enriquez-Urzelai et al. 2020 The roles of acclimation and behavior in buffering climate change impacts along elevational gradients. Journal of Animal Ecology.

The dataset file is called "CTs.txt" and contains 10 columns:

1: (Pop) population of origin of each analysed individual.
2: (ID) the identification number of each analysed individual.
3: (treat) the acclimation temperature for the larval stage. Either 14 or 24ºC.
4: (CT) value of critical thermal limit in ºC. Could be either CTmax or CTmin. See column No. 8
5: (S0) survival immediately after critical thermal limits tests. y=yes, n=no
6: (S24) survival 24-h after critical thermal limits tests y=yes, n=no
7: (W) weight when critical thermal limits tests were conducted in mg
8: (min.max) wether CT values correspond to CTmin (min) or CTmax (max)
9: (device) device with which CT tests were conducted
10: (date) date when CT tests were conducted

Please contact Urtzi Enriquez-Urzelai (urtzi.enriquez@gmail.com) with any questions about these data.