Potential effects of climate warming on two species of mountaintop endemic salamanders
During periods of climate warming, species often respond by shifting their distributions towards higher elevations or higher latitudes. However, for species restricted to mountaintops there are no higher elevations, and shifts to higher latitudes would require moving down-slope through warmer regions and the ranges of competing species. For this reason, mountaintop species are expected to be at high risk of extinction from climate warming, particularly when they are surrounded by competing species at lower elevations. We used empirical studies of temperature preferences and activity periods in contact zones to project the effects of climate warming on two species of endemic mountaintop salamanders in the Blue Ridge of Virginia - Plethodon sherando (the Big Levels salamander) and P. hubrichti (the Peaks of Otter salamander). Both of these salamanders have tiny ranges (<100 km2) and are surrounded entirely by Northern Red-Backed salamanders at lower elevations. We monitored the activity periods of Big Levels and Peaks of Otter salamanders relative to Red-Backed salamanders over the course of a year. We then modeled how activity periods changed with respect to soil temperature and soil moisture at sites where the species co-occurred.
Contrary to expectations, both mountaintop endemic species displayed preferences for warmer temperatures as compared to the Red-Backed salamanders that surround them at lower elevations. Big Levels salamanders were active later in the summer as compared to Red-backs, and the proportion of Big Levels salamanders in the sample increased with soil temperature. Peaks of Otter salamanders showed similar activity levels to Red-backs at higher temperatures, but displayed reduced activity compared to Red-backs at lower temperatures. Effects of soil moisture on salamander activity levels were similar for both pairs of species, though no severe droughts were recorded during the sampling period. Our results suggest that the conventional scenario in which climate warming causes competition-driven range contraction for high-elevation species may not be applicable to some mountaintop endemics. Although our results are somewhat counterintuitive, we believe they make sense in light of the evolutionary history of these sets of species and their documented tendency towards niche conservatism in climate tolerance.