Type of Thesis
Ecology and Evolutionary Biology
Daniel Forrest Doak
This study seeks to address the degree to which overwinter snowpack influences individual site-level occupancy of the American pika (Ochotona princeps). There is considerable, but also circumstantial evidence of the importance that snow-cover plays in insulating O. princeps from cold exposure. With future declines in snowpack projected across the range of O. princeps, this paper seeks to address the current absence of data understanding how snowpack reductions may further limit future distributions of climatically suitable pika habitat. The influence of snowpack on pikas was measured by relating the individual-level-scale of occupancy to a high-resolution snow model. The study site spans two high elevation watersheds adjacent to Niwot Ridge on the Front Range of Colorado. Occupancy was measured by direct and indirect detection at 72 sites in August of 2016 and 2017. Over half of surveyed sites had evidence of occupancy. Hypotheses about the effect of snow-cover on pikas were tested using generalized linear mixed-effects models. No effect of snow cover was detected on pika occupancy. Two sources of potential error were identified that might explain the lack of influence of snowpack in the models. Additionally, the snowpack model was highly variable between years and is only available for years 1996-2007, forcing the creation and choice of an averaged snow model. August surveys likely include recently-dispersed juveniles whose presence does not indicate a sufficiently-insulating over-winter snowpack. Proposed solutions to the error within the occupancy data involve stress hormone analysis as well as discarding sites where juvenile-sized scat was collected.
Wasser, Max, "Using High-Resolution Snowpack Models to Explain Patterns of Habitat Loss for the American Pika" (2018). Undergraduate Honors Theses. 1651.