How will Mammals in the Alpine Zone of the Sierra Nevada Mountains Respond to Future Climate?
Our study addresses the general question of the degree to which wildlife species can adapt to, or possibly even modify, effects from climate change. We focused on five species of mammals in the alpine zone of the Sierra Nevada mountain range, including the federally endangered Sierra Nevada bighorn sheep and the American pika, a species recently proposed for listing due to the loss of populations from altered climatic conditions. It was expected that there will be an upward expansion of trees and shrubs from lower elevations and that many or even most alpine meadows will be converted to woody dominated communities. Meadows provide critical habitat for many alpine mammal species, and their conversion could represent a major loss with severe consequences for the long-term persistence of these species. However, it is currently unknown whether the severity of the effects of meadow conversion on alpine mammals would be uniform or species-specific; all species could be impacted similarly; some species could be unaffected; or species currently not considered at risk may be seriously impacted. Moreover, while climate could potentially trigger changes in alpine vegetation communities, herbivorous and granivorous mammals could mediate the magnitude and extent of meadow conversion through their consumption of woody seeds and seedlings. In other words, feedbacks between climate and alpine mammals could result in the mammals “managing their own habitat.” Presently though, very little is known about vegetation or mammal communities in the alpine zone of the Sierra Nevada, especially in relation to climate change. Consequently, resource management agencies are seriously hindered in development of justifiable, long-term management strategies for bighorn sheep, pika, and other alpine mammals. To answer these questions, we modeled (1) the range shifts for five alpine mammal species and (2) the degree to which plant-animal interactions may alter what is often assumed to be an inevitable, climatically driven transition of alpine meadows to woody dominated communities in the Sierra Nevada.