An experimental approach to understanding elevation limits in a montane terrestrial salamander, Plethodon montanus

Understanding the abiotic and biotic factors that determine the limits to species range is an essential goal in ecology, biogeography, evolutionary biology, and conservation biology. Moreover, predictions of shifts in species distributions under future changes in climate can be improved through understanding the spatial variation in survival, growth, and reproduction. A long-standing hypothesis postulates that, for Northern Hemisphere species, abiotic factors like temperature limit northern and/or higher elevation extents, while biotic factors like competition limit the southern and/or lower elevation range edges; though amphibians may not follow this general trend. Therefore, we combined environmental suitability models and a reciprocal transplant experiment across an elevational gradient to explore the role of the abiotic environment on the range limits of a montane salamander (Plethodon montanus). We first determined suitability of the abiotic environment for P. montanus, under current (1960 - 2000) and future (2050) climate scenarios. Second, we collected juveniles from each of three elevations and transplanted them within mesocosms such that each origin population was represented within each transplant location and vice-versa. We found that environmental suitability in 2050 decreased throughout the range compared to current predictions, especially at lower elevations. Additionally, we found that individuals starting body condition and transplant location were important predictors of survival, growth, and reproduction condition; importantly, individuals transplanted to low elevation had lower survival and growth rates compared to those moved to mid or high elevations. Our study provides experimental support that the abiotic environment limits the lower elevation distribution of P. montanus and, unfortunately, our results also paint a possible bleak future for this species and likely other montane terrestrial plethodontids. The abiotic environment, which will become increasingly limited under future changes in climate, was found to have more influence on survival and growth than population identity.