The roles of acclimation and behavior in buffering climate change impacts along elevational gradients

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.