Population resilience in an American pika (Ochotona princeps) metapopulation

Population resilience in a metapopulation of American pikas (Ochotona princeps) at Bodie, California, was investigated with a series of 18 detailed occupancy surveys conducted between 1989 and 2010. These were compared with earlier 1972 and 1977 censuses and earlier historical records of pikas at Bodie. There is concern that American pikas may be increasingly vulnerable to warm temperatures due to climate change, and this investigation represents the longest study of the species in a relatively low-elevation (warm) environment. The Bodie pika population represents one of the best mammalian examples of a classic metapopulation system. Annual number of observed patch extinctions (total = 114) and recolonizations (109) varied greatly among the 18 census intervals. There has been no decline in percent of patches occupied in the northern half of the study area since 1972, and the number of documented pikas in the north in recent surveys exceeded the numbers found in 1972 and 1977. In contrast, the southern half of the metapopulation collapsed during our study, apparently the result of stochasticity of metapopulation dynamics; no southern patches were occupied after 2006. The potential impact of temperature on metapopulation dynamics was examined using long-term chronic (average summer monthly maximum) and acute threshold (number of days ≥ 25°C and ≥ 28°C within a year) temperatures. There is no evidence that warming temperatures have directly and negatively affected pika persistence at Bodie. Neither warm chronic nor acute temperatures increased the frequency of extinctions of populations on patches, and relatively cooler chronic or acute temperatures did not lead to an increase in the frequency of recolonization events. Warm temperatures, however, could have impeded the dispersal of colonists moving from north to south, thus contributing to the failure of the southern region to become repopulated.