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The objective of this study was to determine differences in small mammal assemblage structure and population dynamics among four oak dominated sites at four different stages of gypsy moth disturbance: a high tree mortality site, a disturbance in process site, a disturbance recovery site, and an undisturbed reference site. More specifically, the study was designed to identify changes in habitat structure that would influence small mammal microdistributions and determine the quality of habitat created by gypsy moth herbivory using demographic structure of <i>Peromyscus</i> populations as an indicator of habitat quality. <i>Peromyscus leucopus</i>, Peromyscus maniculatus, the Soricids, and <i>Clethrionomys gapperi</i> had greater abundances at the disturbed sites relative to the reference site. Gypsy moth disturbance increased the abundance of small mammals and the number of coexisting species within a given area, which was attributed to several changes in habitat structure. The disturbed sites were characterized as having more fallen logs and standing dead snags, greater shrub and herbaceous cover, and higher invertebrate abundances relative to the reference site. These changes in habitat structure provided small mammals with increased cover from avian predators, more food resources, and potential nesting cavities. <i>P. leucopus</i> populations at the high mortality site exhibited greater demographic stability than the reference Site populations. This was marked by higher proportions of females, smaller density fluctuations, more fall recruitment of young, higher residency, and lower proportions of males. Strong evidence for density-dependent population regulation was observed for <i>P. leucopus</i> populations at the high mortality site and the <i>P. maniculatus</i> population at the recovery site. At high densities these populations exhibited extensive intraspecific microhabitat segregation. Female adults segregated from juveniles and male adults into more optimal microhabitats. Male adult microhabitat use significantly differed from male juvenile microhabitat use. The exclusion of young mice from optimal microhabitats by adults may be a mechanism by which adults limit over-exploitation of resources by subordinate members of the population at high densities. The results of this study suggest that gypsy moth disturbance of areas dominated by chestnut oaks at least temporarily improves habitat quality for small mammals. / Master of Science

The landscapes of the Great Basin and Mojave Deserts are changing due to plant invasion. Highly flammable invasive grasses increase the size and frequency of fire causing a cascade of effects through the plant and animal communities. One of the most influential animal groups in desert systems is small mammals. We sought to learn how small mammals are impacted by fire and how their influence on the plant community differs between burned and unburned habitat. Small mammals did not have higher rates of mortality as a direct result of a controlled burn. In the Great Basin, there were short-term reductions in abundance, richness, and diversity of the small mammal community in burned plots. In the Mojave, species richness and diversity increased in burned plots shortly after fire and no abundance differences were detected. These results correspond with our prediction based on the dominant small mammal species at each site. Small mammals are primarily granivores; however, they also have strong impacts on the plant community via folivory. We tested for small mammal impacts on seedling survival in burned and unburned habitat. Small mammal access, burned vs. unburned habitat, and plant species were all important determinants of survival. Small mammals greatly reduced survival at both sites in burned and unburned habitat and often had a stronger impact in unburned than burned plots. Accounting for small mammal folivory may be a crucial step in successful post-fire rehabilitation. Finally, we used seed trays to test how small mammals influence the persistence of seed on the landscape. Small mammals reduced persistence of an invasive and native plant species in the Great Basin in 2012, yet a year later when small mammal abundance was reduced, no small mammal effect was observed. In the Mojave, persistence was reduced for the majority of species both years of the study. Small mammals did not appear to avoid seed of invasive plant species as we had predicted and may be important consumers reducing the reproductive potential of these invaders. If small mammals do prefer non-native seedlings over natives and are also consuming non-native seed, they may be greatly reducing the presence of non-natives both on the unburned landscape as well as after fire. Non-native consumption by small mammals could aid in the biotic resistance of these desert ecosystems. This research further enforces the important role that small mammals play as consumers, dispersers, and regulators of the plant community.