Elevation-restricted species have contributed greatly to our understanding of the causes of species range limits. Mountaintop endemics are typically thought to have ranges that are restricted by temperature, making these species particularly susceptible to the effects of climate warming. We carried out both field and lab studies of the causes of range limits in the Peaks of Otter salamander (Plethodon hubrichti), a mountaintop endemic restricted to a small range in the Blue Ridge Mountains of Virginia. We used year-round surveys of activity levels within contact zones to estimate the relative temperature tolerance of Peaks of Otter salamanders and the common Redback salamanders that surround them at lower elevations. We also collected demographic measurements within contact zones to examine how body condition, reproductive success, and tail loss (an indicator of interference competition or predation) varied across contact zones.
Both field and lab studies indicate that, contrary to expectations, Peaks of Otter salamanders are active at warmer temperatures than the more common Redback salamanders that surround them. Detailed measurements of demographic correlates through contact zones suggest that neither salamander body condition nor average reproductive success changes for either species across contact zones. However, we did find surprisingly high levels of tail loss in Peaks of Otter salamanders within contact zones, suggesting a role for interference competition or selective predation in determining their range limits. Our results demonstrate that simple hypothesis about temperature-dependence may be inadequate to explain some mountaintop distributions and that careful attention to the nature of species interactions can provide important insights on the processes that determine range limits.