Date of Award
Master of Science (MS)
Saara DeWalt, Committee Chair
Over the next century, temperatures are expected to rise by 1-4 °C in the Greater Yellowstone Ecosystem of the American West, and by even larger amounts in montane habitats. This warming may cause species that live there to acclimate, adapt, move, or disappear. Understanding the degree to which species' distributions are tied to temperature and other aspects of the environment is key to developing effective conservation plans. American pikas (Ochotona princeps) are small alpine lagomorphs restricted to cooler talus habitats. Pikas have exhibited varying responses across their range to the changing climate, suggesting that their distributions are not simply limited by climate. In this thesis, I explored how landscape, climate, vegetation, habitat connectivity and activity constraints are related to pika distribution and abundance in the northern range of the Greater Yellowstone Ecosystem including the Beartooth Plateau, Washburn Mountain, and Bunsen-Hoodoo area.
To determine the environmental variables that best explain pika distribution and abundance, I compared statistical models with different sets of environmental variables and field measurements of occupancy and pika latrine densities, as a proxy for pika density. The strongest predictor of pika occupancy was the timing of peak vegetation cover (measured as the maximum Normalized Difference Vegetation Index), with higher occupancy at sites with later peaks in vegetation cover. Habitat connectivity, measured by the percentage of talus within 1 km of each site, was the second strongest predictor of occupancy, with occupancy increasing with the amount of nearby talus. Neither maximum summer temperatures nor the number of hours pikas could be active during the summer were strong predictors of occupancy. Overall, there was a higher probability of occupancy at sites with increased connectedness to surrounding talus, peak primary productivity later in the year, and large amounts of seasonal precipitation. The necessity of large seasonal precipitation may be detrimental for pika populations because, under future climate scenarios, this area is expected to become drier.
The two strongest predictors of latrine density, and likely pika density, were the area of talus sites and the forage quality, as measured by the ratio of forbs to graminoids. Latrine density was greater in areas of higher amounts of forbs compared to graminoids, flatter slopes and smaller talus areas. As with site occupancy, summer temperatures and activity hours were not the strongest predictors of latrine density. Instead, winter temperatures and winter and summer precipitation were the strongest climate predictors of latrine density.
In conclusion, forage quality and habitat connectivity appear to drive the distribution and abundance of pikas in the Greater Yellowstone Region. In particular, the Beartooth Plateau appears to provide a refugia for pikas under the present and potentially the future climate. Summer temperatures do not appear to limit pikas in this region; instead they are limited by winter climate. Ultimately, identifying areas of large connectivity, such as the Beartooth Plateau, and high forage quality, will be necessary for future protection of this species.
Hanley, Kaitlyn, "Environmental Determinants of American Pika (Ochotona princeps) Distribution and Abundance Across the Northern Portion of the Greater Yellowstone Ecosystem" (2019). All Theses. 3050.