Date of Award

Spring 1-1-2013

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Ecology & Evolutionary Biology

First Advisor

Robert Guralnick

Second Advisor

Chris Ray

Third Advisor

Christy McCain

Fourth Advisor

Daniel Doak

Fifth Advisor

Andrew Martin

Abstract

Climate change is affecting ecosystems worldwide. Among those ecological communities most affected are those inhabiting alpine habitats. These communities have evolved key adaptations to thrive in cold, wet environments. As temperatures warm and precipitation patterns become more variable due to global climate change, many alpine species are expected to be impacted. This dissertation research focuses on the American pika, a small lagomorph inhabiting broken rock slopes in the mountains and high plateaus of western North America. Population declines in the Great Basin region at the end of the 20th Century caused concern for populations elsewhere in the species range. The goal of this dissertation work was to document pika occupancy and density throughout the Southern Rocky Mountain region. Occupancy and density trends were modeled using potential climate- and habitat-based predictors known to impact pikas elsewhere in the species’ range. Survey sites were selected from among hundreds of locations known to be occupied by pikas prior to 1980. In 2008, modeling of the resurvey results from 69 of these sites indicated that mean annual precipitation plays an important role in maintaining pika populations in this region. Further surveys of 19 of these sites in 2009-2011 showed a shift toward mean summer temperature and forage quality as the top predictors of occupancy, though sites lacking pikas also remained drier than those with pikas throughout this survey period. Pika occupancy in this region was relatively high, with Southern Rockies occupancy rates ranging from 74% to 94%. Among the extant populations, variability in population densities were best explained by patch area and vegetation quality: the highest density populations were reported in regions with small patches of talus, high forb diversity, and low graminoid to forb ratios. These results suggest that intraspecific competition for food resources strongly influences pika density. As climate change continues, vegetation quality is expected to decline in pika habitats. Given this species’ reliance on cool, wet climates with high forb content, continued changes toward drier, hotter, and more graminoid-dominant habitats are likely to lead to declines in both pika densities and occupancy throughout the Southern Rockies and the western United States.

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