Theses and Dissertations at Montana State University (MSU)
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Item Assessing alternative drivers of occupancy, abundance, and elevational range retraction at the range core of a climate-sensitive mammal(Montana State University - Bozeman, College of Letters & Science, 2020) Billman, Peter Donn; Chairperson, Graduate Committee: David McWethyEcological niche theory and niche conservativism suggest that rising temperatures globally will continue pressuring species to track cooler environments. Examining changes in occupancy and abundance together across bioclimatic gradients can inform forecasts of expected range shifts. Although occupancy and abundance reflect similar aspects of species-environment relationships, they are governed by different underlying processes. Abundance is thought to be more reflective of shorter-term conditions affecting vital rates, whereas site occupancy often reflects habitat suitability. By directly comparing results of both response types, as well as elevational range retraction, we offer a robust method for assessing complex species-climate relationships. In this study, we test how populations of the American pika (Ochotona princeps), a small montane lagomorph, respond to varying climatic conditions. To do so, we tested and compared the drivers of site occupancy, abundance, and upslope retraction, across 760 talus patches, nested within 64 watersheds across the Northern Rocky Mountains, USA. Using mixed-effects modeling, paired with an information-theoretic approach, we tested model suites that reflected hypothesized species-climate relationships to identify the top models of each of our response classes. Approximately one third (33.9%) of patches were found extirpated. The most important environmental predictors differed among occupancy, abundance, and amount of upslope retraction. For site occupancy, the top model included metrics of summer acute heat stress, actual evapotranspiration, and habitat availability. For abundance, acute heat stress and the preceding winter's mean temperature (i.e. chronic cold stress) was the top-ranked model, suggesting rapid responses of populations to recent climatic conditions. Furthermore, we found that a model including both chronic heat and chronic cold stress best predicted the total amount of vertical retraction across watersheds, whereas acute heat stress and summer precipitation best explained the residuals. Our results emphasize the complexity associated with evaluating species responses to environmental change and that results from occupancy analyses should be used with caution when extrapolating to predicting abundances across varied landscapes. Our method for assessing the drivers of elevational retraction across a suite of watersheds has widespread applications for evaluating species response to changing climatic conditions elsewhere.Item Investigating occupancy and density of American pikas (Ochotona princeps) across precipitation gradients in the Intermountain West, USA.(Montana State University - Bozeman, College of Letters & Science, 2017) Thompson, William Wesley; Chairperson, Graduate Committee: Laura Burkle; Erik Beever (co-chair)Anthropogenic climate change is altering species distributions and abundances of diverse taxa across the globe. Understanding the mechanisms underlying these shifts in distributions and abundances may provide a more complete understanding of species responses to climate change. Using an indicator species for climate change (the American pika, Ochotona princeps), we surveyed 200 talus patches in 2015-2016 across four study areas that spanned a precipitation gradient in the Intermountain West, USA. Our results yielded unexpected insights into the climatic associations underlying pika distributions and abundances. Contrary to our expectation, warmer average winter temperatures were negatively associated with pika occupancy and relative density, and further investigation revealed that winter temperatures rarely reached low enough thresholds to be considered thermally stressful. While the winter of 2015-2016 was the warmest winter on record for the contiguous United States, these results may foreshadow how montane species may respond to future climate conditions. Climate water deficit was another top-predictor of pika occupancy and relative density across spatial and temporal scales. Increasing values of climate water deficit were negatively associated with pika occupancy and relative density. This measure of soil drought has gained little attention for predicting animal distributions and abundances. Unexpectedly, we found increasing (rather than decreasing, as found by other research) cover of graminoid species to correlate positively with relative pika density, indicating that increasing cover of graminoids were associated with increasing relative density. Pikas have been suggested to prefer plants higher in secondary compounds (forbs, trees, and shrubs); however, we did not find this. Pikas have also been suggested to gain most of their water via metabolic water. Given the diuretic effects of many of these secondary compounds, and the negative relationship observed with soil drought, these results could suggest an interaction between climate water deficit and forage preference; in which pikas prefer plants lower in secondary compounds at drier sites. Our results emphasize the need to clarify mechanisms underlying species responses to recent climate change, to better inform management decisions and conservation planning.Item Influences of abiotic and biotic habitat characteristics on pika occupancy in select regions of the Gallatin National Forest, Montana(Montana State University - Bozeman, Graduate School, 2015) Hall, Lindsay Paterson; Chairperson, Graduate Committee: Peggy Taylor.This research project explores how several abiotic and biotic habitat characteristics influence occupancy probabilities of the North American pika, Ochotona princeps within select regions of the Gallatin National Forest. Pikas are possible indicator species for climate change, as they are obligatory talus dwellers found in alpine and subalpine ecosystems, and are extremely sensitive to high temperatures. Slope, aspect, elevation, talus field dimensions, and mean boulder size likely influence how pikas experience ambient temperatures within specific habitat sites and consequently may influence occupancy probabilities. In addition, vegetation diversity and abundance may also influence the likelihood of a talus field being occupied by pikas. I investigated the relationship between abiotic and biotic habitat site characteristics and pika occupancy. I visited three sites within the Gallatin National Forest: Beehive Basin, Portal Creek, and Hyalite Canyon during the summer and fall of 2014. I surveyed 28 talus fields, quantifying a suite of habitat variables and determining pika occupancy of each site. The results of this study indicate that slope, aspect, and elevation were the strongest predictors of pika occupancy, whereas solar insolation, talus field area, mean boulder size, and distance to nearest neighbor were of less importance. Additionally, vegetation type and abundance did not prove statistically significant as a predictor of pika occupancy. Broadly speaking, pika occupancy within the Gallatin National Forest will likely depend on specific combinations of local abiotic and biotic habitat attributes.Item Daily and seasonal activity patterns of the pika in southwestern Montana(Montana State University - Bozeman, College of Letters & Science, 1987) Moore, Robin Lee Kistler