Modeling contemporary range retraction in Great Basin pikas (Ochotona princeps) using data on microclimate and microhabitat

The American pika (Ochotona princeps) inhabits talus slopes on isolated mountaintops in the Great Basin, where the species is susceptible to localized extirpations. Previous studies from the region related pika extirpations to proxies for climate and habitat quality, or to relatively short datasets on microclimate. This study extends previous research by modeling extirpation using new data from microclimates and microhabitats, and by including data on the vegetation available to individual pikas. We re-surveyed 25 sites historically occupied by pikas, and collected microclimatic and vegetative-cover data from each site. Sites of pika extirpation experienced higher summer temperatures and higher frequency of extremely warm days during 2005–2007 than did sites of pika persistence. Several aspects of vegetative cover also differed between persistence and extirpation sites, and relative forb cover was positively related to pika persistence. Evaluation of competing models within an information-theoretic framework suggests strong support for recent mean summer temperature as the primary driver of extirpations in this dataset. In agreement with other modeling efforts, this result supports the hypothesis that extirpation results from chronic heat stress during the summer months when pikas must gather and store food for the winter. In contrast with previous studies, we found less support for the hypothesis that extirpation results from acute cold stress during the winter months, possibly due to several differences in analytical methods.