Variation in habitat characteristics of American pikas along an elevation gradient at their northern range margin.

摘要

Temperature is an important environmental variable in shaping the distribution of species. The American pika (Ochotona princeps) has been identified as a climate-change-sensitive species as documented by the extirpation of a number of populations at the southern end of the species' range. Limited tolerance to warm temperatures has previously been reported, yet recent evidence suggests that pikas are able to live outside of cool habitats with the discovery of warmer, low-elevation pika populations, such as those found in the Bella Coola Valley in British Columbia. Here we characterize the temperatures experienced by pikas living along an elevation gradient at the northern end of their distribution. Additionally, we recorded temperatures both above and below the talus at one of our sites and the relationship between pika activity and temperature. Temperatures differed along the elevation gradient by up to 6 degrees C from low- to high-elevation sites. Below-talus temperatures were lower than above-talus temperatures at noon and during the afternoon, and were warmer than above temperatures in the morning and night, suggesting that talus has insulative properties that guard against extreme temperatures. Lastly, a negative relationship was observed between temperature and pika activity. We show that although at the northern end of pika distribution, ambient temperatures 1.5 m above the talus surface often exceeded the threshold for acute heat stress. Our results also suggest that behavioral thermoregulation or other adaptations may enable pikas to inhabit low-elevation habitat that was previously thought as inhospitable to pikas.