Too hot to trot? Pika survival in a time of global change
Across many taxa, habitat specialists are suffering particular declines due to climate change, presumably because they are less flexible than generalists in adapting to novel climates or to the changing availability or quality of food resources. American pikas (Ochotona princeps) are excellent indicators of climate change in alpine ecosystems because of their strict habitat requirements, limited dispersal ability, and sensitivity to high ambient temperatures. Population declines, upslope range retractions and local extinctions have already been widely documented in parts of the pika’s range. However, despite this reliance on cold climates, pikas thrive near sea level in the warm temperate rainforests of the Columbia River Gorge (CRG), well outside of their previously recognized climatic niche. How do pikas survive in this seemingly unsuitable climate? To address this question, we conducted vegetation surveys and deployed temperature dataloggers at four low elevation sites in the CRG and two high elevation sites on nearby Mt. Hood. We also observed over 220 hours of pika behavior at two sites in the CRG to document foraging and caching behavior.
CRG talus was unique in having high moss coverage (40-80%) compared to alpine sites (<15%). Moss also comprised the majority of pikas’ diet in the CRG. Finally, summer temperatures at and below the talus surface at moss-covered sites in the CRG were up to 15°C cooler than at CRG sites with low moss cover or high elevation habitat on Mt. Hood. Moss cover appears to serve a dual function for pika survival. First, it releases pikas from constructing large food caches (i.e., because vegetation is available through the winter). Thus, surface activity requirements and predation pressure during the summer can be greatly reduced compared to high elevations. Second, moss cover appears to buffer against high summer surface temperatures in the CRG. Taken together, these results suggest that CRG pika populations may actually be better protected from the effects of climate change than their counterparts living in the high mountains, who must construct substantial haypiles during the warmest parts of the summer. In addition, these results suggest that pikas are extremely flexible in their diet if given an appropriate thermal microclimate. These results advance our knowledge of pikas’ true habitat requirements and climate sensitivity, and may also inform conservation plans.