Theses and Dissertations at Montana State University (MSU)
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Item Linking plant and soil nutrient dynamics in temperate and tropical montane forests(Montana State University - Bozeman, College of Letters & Science, 2018) Qubain, Claire Anne; Chairperson, Graduate Committee: David Roberts; Jia Hu (co-chair); Yuriko Yano and Jia Hu were co-authors of the article, 'Linking nitrogen allocation in douglas-fir to soil nitrogen availability in a western montane conifer forest' submitted to the journal 'Oecologia' which is contained within this thesis.; Diego Riveros-Iregui and Jia Hu were co-authors of the article, 'Climate and invasion drive soil nutrient dynamics in tropical montane forests of the Galapagos archipelago' submitted to the journal 'Ecology' which is contained within this thesis.I built on our fundamental understanding of ecosystem function by examining how climate variability influences feedbacks between plant processes and soil nutrient dynamics. At Lubrecht Experimental Forest, I examined how variability in snow depth, precipitation, and soil moisture influenced seasonal nitrogen allocation in Douglas-fir. I then examined if N cycling within Douglas-fir synchronized with patterns of N availability in the soil. In this case, N availability in the soil influenced plant nutrient dynamics. On the other hand, on San Cristobal Island in the Galapagos Archipelago, plants fed back and influenced soil nutrient dynamics. Changes in precipitation, soil moisture, and temperature strongly controlled nutrient concentrations in the soil, and to a lesser degree, plant community type determined nutrient concentrations, especially N concentrations, in the soil.Item Effects of seasonal precipitation and habitat associations on the demographics of Mexican spotted owl prey in the canyonlands region of southern Utah(Montana State University - Bozeman, College of Letters & Science, 2018) Thornburg, John Ramsey, III; Chairperson, Graduate Committee: David WilleyMost food habit studies of Mexican Spotted Owls (Strix occidentalis lucida) have been conducted in forested environments in more southern portions of their range. Through regurgitated pellet analyses, these studies showed the majority of Mexican Spotted Owl prey consumed was comprised of Cricetid rodents, specifically woodrats (Neotoma spp.) and white-footed mice (Peromyscus spp.). In the northernmost portions of their range, Mexican Spotted Owls inhabit rocky canyon habitats within the Colorado Plateau. In the canyonlands region, few studies have investigated the population ecology and habitat associations of the primary prey of spotted owls and no studies have examined the relationships among primary prey demographics and their responses to seasonal precipitation. Given the Mexican Spotted Owls status as a threatened species, increased knowledge of prey species relationships with climate and habitat may assist in future management of spotted owl populations across the canyonlands region. Using a seven-year historic data set collected at three study sites in Grand Staircase -- Escalante National Monument from 2001 to 2007 and three years of data collected at five study sites in Capitol Reef National Park from 2013 to 2015, I described the nocturnal small mammal communities, investigated primary prey habitat and microhabitat component associations, and investigated the effects of timing and amount of seasonal precipitation on primary prey abundance and diversity in both study areas. Cricetid rodents were the most abundant nocturnal small mammals and potential prey available for spotted owls inhabiting rocky canyon habitats. Microhabitat analyses revealed Cricetid rodents partitioned space and resources that minimized interspecific competition enabling coexistence in narrow canyon systems with limited biological resources. Linear mixed-effects modeling indicated winter precipitation was the primary driver of spotted owl primary prey demographics in the canyonlands region.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.