Scholarship & Research
Permanent URI for this communityhttps://scholarworks.montana.edu/handle/1/1
Browse
2 results
Search Results
Item Cheatgrass invasion of sagebrush steppe : impacts of vegetation structure on small mammals(Montana State University - Bozeman, College of Letters & Science, 2014) Bachen, Daniel Allen; Chairperson, Graduate Committee: Andrea Litt; Andrea R. Litt and Claire Gower were co-authors of the article, 'Effects of cheatgrass invasion on food accessibility for small mammals in sagebrush steppe' submitted to the journal 'Journal of wildlife management' which is contained within this thesis.; Andrea R. Litt and Claire Gower were co-authors of the article, 'Changes in predation risk for deer mice (Peromyscus maniculatus) with plant invasions: understanding mechanisms' submitted to the journal 'Journal of wildlife management' which is contained within this thesis.Nonnative plants can affect habitat quality for native animals directly, through changes in resources like cover or food, and indirectly, through changes in access to resources or predation risk. Understanding these effects is crucial to develop management techniques and maintain ecosystem processes. In sagebrush steppe, brome grasses such as cheatgrass (Bromus tectorum) can invade and form dense stands, increasing the depth and persistence of litter, as well as the density of standing vegetation. These structural changes alter abundance and composition of the small mammal community. We used a series of experiments to explore whether changes in vegetation structure associated with the invasion of cheatgrass would alter foraging and predation risk of small mammals, to better understand mechanisms driving documented population- and community-level effects. In the first experiment, we placed a measured amount of grain at stations with either increased litter or stem density, and examined how much grain was removed nightly. We found that adding litter reduced the amount of grain removed in 2 of our 3 study areas. In the second experiment, we timed animals fleeing a simulated predator through various depths of litter or densities of stems. We found that dense stems impeded movement more than litter. In the third experiment, we recorded animals moving through native sagebrush steppe and cheatgrass monocultures, and analyzed these recordings to detect differences in the volume of noise created, especially for frequencies detected by common predators. We found that animals moving through cheatgrass made more noise at high frequencies, compared to native sagebrush steppe. Based on these experiments, cheatgrass monocultures may reduce habitat quality for small mammals by decreasing foraging efficiency and increasing vulnerability to predators. Mitigation strategies should focus on reducing the density of standing vegetation where predation is a limiting factor and litter depth where small mammals are food-limited.Item Bird response to landscape pattern and disturbance across productivity gradients in forests of the Pacific Northwest(Montana State University - Bozeman, College of Letters & Science, 2007) McWethy, David Burch; Chairperson, Graduate Committee: Andrew HansenManaging forest lands for biodiversity is a common goal in the public and private forests of the Pacific Northwest and is typically achieved through harvests that result in an array of vegetation structural conditions that provide suitable habitat for a number of species. The assumption is made that the causative factors of biodiversity do not vary geographically and that silviculture, as a management tool, can be applied similarly across different biophysical locales. The primary aim of this research is to better understand how species respond to both local and landscape-scale forest structural conditions in landscapes with different levels of productivity (e.g. gross primary productivity). We hypothesized that the influence of landscape effects on bird richness, abundance and community organization would be more pronounced in highly productive environments. We also hypothesized that species response to disturbance would differ across gradients in ecosystem productivity. We predicted that bird diversity would increase with increasing disturbance extent where favorable climatic conditions result in high levels of competitive exclusion. Alternatively, we predicted that bird diversity would decrease with increasing disturbance extent when factors other than competition limit or regulate bird species diversity.