The objective of this dissertation was to examine how ecological and micro-evolutionary factors may influence the response of alpine mammals to reductions in habitat quality projected under climate change using the American pika (Ochotona princeps) as a model system. I begin with an overview of anthropogenic impacts on global ecology and ecosystem functioning with an emphasis on the vulnerability of mountain systems to environmental change. I then introduce the American pika and discuss contemporary population loss across the species’ range particularly at the southern end of its distribution in the Great Basin and northeastern California where the regional effects of climate change are expected to increase the co-occurrence of warm and dry conditions over the next few decades. In Chapter 1, I explore the effects of site, season, territory quality (microclimate temperature data) on patterns of physiological stress (via corticosterone stress hormones) in two high-elevation sites in the eastern Sierra Nevada. In Chapter 2, I examine the effects of habitat fragmentation on patterns of long-term pika occupancy as measured by 40 years of census data, and its association with habitat quality (patch perimeter and size), physiological stress, and climate variables calculated from local weather station data for a pika population located at the southern end of the species’ range. In Chapter 3, I track changes in the structure and distribution of genetic variation, effective population size, and movement patterns over the last 65 years within this same vulnerable pika population through the use of historical and contemporary genetic datasets. In Chapter 1, I found that patterns of stress differed significantly among pikas at two sites despite close geographic proximity and that the effects of site, year, territory, and individual diversity on patterns of pika stress were substantial compared to the relatively minor effects of microclimate predictors. In Chapter 2, I discovered significant associations among pika occupancy, temperature patterns, and stress hormone concentrations that suggest a role of individual physiologic response in demographic stability. Finally, in Chapter 3, I provide evidence of genetic erosion and its putative relationship with local climate for a genetically unique pika population at risk of extirpation
