Conservation status of American pikas (Ochotona princeps)

The American pika (Ochotona princeps) is commonly perceived as a species that is at high risk of extinction due to climate change. The purpose of this review is two-fold: to evaluate the claim that climate change is threatening pikas with extinction, and to summarize the conservation status of the American pika. Most American pikas inhabit major cordilleras, such as the Rocky Mountain, Sierra Nevada, and Cascade ranges. Occupancy of potential pika habitat in these ranges is uniformly high and no discernible climate signal has been found that discriminates between the many occupied and relatively few unoccupied sites that have been recently surveyed. Pikas therefore are thriving across most of their range. The story differs in more marginal parts of the species range, primarily across the Great Basin, where a higher percentage of available habitat is unoccupied. A comprehensive review of Great Basin pikas revealed that occupied sites, sites of recent extirpation, and old sites, were regularly found within the same geographic and climatic space as extant sites, and suggested that pikas in the Great Basin tolerated a broader set of habitat and climatic conditions than previously understood. Studies of a small subset of extirpated sites in the Great Basin and in California found that climate variables (most notably measures of hot temperature) were associated more often with extirpated sites than occupied sites. Importantly, upward contraction of the lower elevation boundary also was found at some sites. However, models that incorporated variables other than climate (such as availability of upslope talus habitat) often were better predictors of site persistence. Many extirpations occurred on small habitat patches, which were subject to stochastic extinction, as informed by a long-term pika metapopulation study in Bodie, California. In addition, several sites may have been compromised by cattle grazing or other anthropogenic factors. In contrast, several low, hot sites (Bodie, Mono Craters, Craters of the Moon National Monument and Preserve, Lava Beds National Monument, Columbia River Gorge) retain active pika populations, demonstrating the adaptive capacity and resilience of pikas in response to adverse environmental conditions. Pikas cope with warm temperatures by retreating into cool interstices of their talus habitat and augment their restricted daytime foraging with nocturnal activity. Pikas exhibit significant flexibility in their foraging tactics and are highly selective in their choice of available vegetation. The trait that places pikas at greatest risk from climate change is their poor dispersal capability. Dispersal is more restricted in hotter environments, and isolated low-elevation sites that become extirpated are unlikely to be recolonized in a warming climate. The narrative that American pikas are going extinct appears to be an overreach. Pikas are doing well across most of their range, but there are limited, low-elevation losses that are likely to be permanent in what is currently marginal pika habitat. The resilience of pikas in the face of climate change, and their ability or inability to persist in marginal, hot environments, will continue to contribute to our understanding of the impact of climate change on individual species.

Isotopic niche of the American pika (Ochotona princeps) through space and time

Anthropogenic climate change is influencing the ecology and distribution of animals. The American pika (Ochotona princeps (Richardson, 1828)) is considered a model species for studying the effects of climate on small alpine mammals and has experienced local extirpation across its range. Using stable isotope analysis of two seasonal molts and bone collagen, we characterize the isotopic carbon and nitrogen niche of pika populations across their range and through time. We find pika isotopic diet to be stable across both time and space compared with other animals and considering the geographic and environmental extent of their range. We find that climatic, not geographic, factors explain part of the isotopic variation across their range. Both δ13C and δ15N from the fall-onset molt decrease with relative humidity of the environment and δ15N values from bone collagen increase with temperature and precipitation. We find a small but significant seasonal difference in δ13C, which could be explained by microbial enrichment of cached haypiles. We establish a baseline of pika isotopic diet and patterns related to climate across their range. We conclude that differences in isotopic signature between pika populations likely reflect the physiology of their forage plants in different environmental conditions.