Revisiting the past to foretell the future: summer temperature and habitat area predict pika extirpations in California

Aim: The American pika (Ochotona princeps) appears to have experienced climate-mediated upslope range contraction in the Great Basin of North America, but this result has not yet been extended to other portions of the pika's range. Our goals were: first, to determine the environmental parameters that most influence current pika distribution within California; second, to infer whether these constraints explain extirpations that have occurred in California; third, to predict future extirpations; and fourth, to advance methods for assessing the degree to which pikas and other climate-sensitive mammals are threatened by climate change.

Location: Historical pika record locations in California, USA, spanning four degrees of latitude and longitude, from Mount Shasta to the southern Sierra Nevada.

Methods: We identified 67 precise historical pika record locations and surveyed them exhaustively, over multiple years, to determine whether pika populations persist at those sites. We used an information theoretic approach and logistic regression to model current pika occupancy as a function of 16 environmental variables, tested our best-performing model as a predictor of historical occupancy, and then used our model to predict future pika occupancy given anticipated climate change.

Results: Pikas no longer occurred at 10 of 67 (15%) historical sites in California. The best predictors of occupancy were average summer temperature and talus habitat area within a 1-km radius. A logistic model fitted to this relationship correctly predicted current occupancy at 94% of sites and correctly hindcasted past occupancy at 93% of sites, suggesting that the model has strong temporal transferability. Depending on the future climate scenario, our model projects that by 2070 pikas will be extirpated from 39% to 88% of these historical sites in California.

Main conclusions: Our simple species distribution model for pikas performs remarkably well for both current and historical periods. Pika distribution appears to be governed primarily by behavioural restrictions mediated by summer temperature and by the configuration of talus habitat available to pikas locally. Pikas, and other montane species in the western USA, may be subjected to above-average exposure to climate change because summer temperature is projected to rise more than annual temperature.