Thermal tolerances in Andean frogs: Are high-elevation species more vulnerable to climate warming?

Background/Question/Methods   Amphibians are declining worldwide, but declines are particularly dramatic in tropical mountains where high endemism and vulnerability to introduced disease is leading to catastrophic extinctions. One the most important aspects of climate change in tropical mountains is the increase in temperature, which in the tropical Andes is accelerating deglaciation and is projected to reach 2–7ºC by 2100. Models based on organismal physiology predict that tropical ectotherms will be severely impacted by climate warming. In order to better understand the potential effects of climate warming in montane frogs, we measured the tolerance to heat stress in 15 species along an elevational transect between 1200 and 3700 m in the eastern slopes of the Andes (Manu National Park, Peru). We used the loss of righting response to measure the critical thermal maximum of frogs in the species-rich family Strabomantidae.

Results/Conclusions   We found that critical thermal maxima decreased with elevation across strabomantid frogs and within species, but not as steeply as ambient temperatures. Consequently, thermal tolerance (the difference between the critical thermal maximum and the maximum ambient temperature at the corresponding elevation) increased with elevation, indicating that frogs at lower elevations are more vulnerable to thermal stress under a global warming scenario than frogs at higher elevations. This finding is not consistent with the fact that most threatened frogs are found at higher elevations. Our results suggest that climate warming is not the main driver of amphibian declines, which disproportionally affect high-elevation taxa.