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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.

The introduction and establishment of exotic species can profoundly alter ecosystems. Two exotic species drastically changing the landscape of deserts in western North America are Bromus tectorum L. and Bromus rubens L. Through the buildup of biomass and slow decomposition rates in deserts these two exotic annual grasses can alter fire regimes that change the plant and animal community dynamics in the ecosystems. To better understand the ecological mechanisms that could restrict or alter the patterns of invasive plant establishment we established a replicated full factorial experiment in the Great Basin and Mojave Desert. The combinations of factors being manipulated are burned or intact plant communities, and presence or exclusion of small mammals. Generally invasive species establishment is thought to be a result of competitive superiority or lack of natural enemies, but if that is the case then why do not all invasive species establish and become highly abundant in their new ecosystems? To understand why some invasive species establish and others do not we monitored three dominant exotic species from the Great Basin and the Mojave Desert, B. tectorum, Halogeton glomeratus (M. Bieb.) C.A. Mey., and B. rubens. We observed that the presence of small mammals create a biotic resistance to B. tectorum, H. glomeratus, and B. rubens. This pattern was observed in both intact and burned plant communities; however, it was most prevalent in the burned plant communities. The strength of the biotic resistance on these invasive species varied between species and the years sampled. In deserts both plant and small mammal communities are tightly tied to precipitation. We wanted to understand how invasive species establishment is affected by small mammal presence after a fire disturbance, and manipulating total precipitation. Total precipitation was manipulated through three different treatments: 1) drought or 30% reduction of ambient precipitation; 2) ambient precipitation; 3) water addition or an increase of 30% ambient precipitation. We focused on B. rubens establishment in the Mojave Desert as our model organism by monitoring it beneath rain manipulation shelters nested in burned/intact and small mammal presence/absence full factorial plots. What we observed was that again small mammals created a biotic resistance on the density of B. rubens regardless of the burn or precipitation treatments. This biotic resistance also translated into decreasing B. rubens biomass and seed density. Under the drought and ambient precipitation treatments we found that small mammals kept the density and biomass equal but under increased precipitation the efficacy of biotic resistance on B. rubens density and biomass was lessened by the availability of the added water.

Early human activity in the arid west has been of interest for many researchers over the last century. However, relatively little is known about Paleoarchaic occupants of the Colorado Plateau and Great Basin because stratified Paleoarchaic sites in these regions are rare. Linked with the climatic Late Pleistocene/Early Holocene transition, the Paleoarchaic to Early Archaic transition has also captured interest in the central Great Basin with recent data coming out of Bonneville Estates Rockshelter—a site containing Pre-Archaic and Early Archaic components in eastern Nevada. These new data provide a model for testing differences in the chipped stone assemblage inferring changes in residential mobility at a new Paleoarchaic site on the Northern Colorado Plateau. Recently excavated, North Creek Shelter (42GA5863) is the only known stratified Paleoarchaic site on the Colorado Plateau for which we have data. Located in south-central Utah, this site was occupied during both the Paleoarchaic (~10,000-9,000 rcybp) and Early Archaic (~9,000-8,000 rcybp) time periods. Differences in the chipped stone assemblage inferring residential mobility between these time periods will be evaluated using Ted Goebel's (2007) model from Bonneville Estates Rockshelter. Based upon Bonneville Estates Rockshelter's lithic assemblage, Goebel inferred that the Pre-Archaic occupants exhibited higher levels of residential mobility than subsequent Early Archaic occupants. A similar tendency was expected for the Paleoarchaic occupants of North Creek Shelter; however, it appears that there is little difference between the North Creek Shelter Paleoarchaic and Early Archaic chipped stone assemblages inferring differences in residential mobility. What little difference there is may be the result of multiple factors, but if it is the result of residential mobility, then the data suggest that North Creek Shelter Paleoarchaic occupants were only slightly more mobile than the Early Archaic occupants.

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No description available.

Thesis (M. En.)--Miami University, Institute of Environmental Sciences, 2004. / Title from first page of PDF document. Includes bibliographical references (p. 31).

The dark kangaroo mouse, Microdipodops megacephalus, is a sensitive species in the Great Basin Desert. This thesis explores the structure of desert rodent communities of the Great Basin to better understand M. megacephalus' place in the community and the conditions that promote large and stable populations. To determine community structure, I used nestedness analysis to evaluate 99 communities of nocturnal granivorous rodents. I found that the community structure was non-random, indicating the existence of assembly rules and ecological constraints. I also found that M. megacephalus was the second most vulnerable species in the community. To explore the correlation between species diversity and relative abundance, I performed regression analyses on M. megacephalus and five commonly co-occurring species of the nocturnal granivore guild: Perognathus longimembris (little pocket mouse), Perognathus parvus (Great Basin pocket mouse), Dipodomys ordii (Ord's kangaroo rat), Dipodomys microps (chisel-toothed kangaroo rat), and Peromyscus maniculatus (deer mouse). Results showed a positive correlation between rodent species diversity and relative abundance for M. megacephalus, P. longimembris, P. parvus, and D. microps, and a negative correlation for D. ordii and P. maniculatus. To further understand community composition, I ran interspecific association analyses based on presence-absence data for the six species using chi-square to determine strength of interspecific associations. I found positive interspecific associations between M. megacephalus and P. parvus, between P. longimembris and P. parvus, between P. longimembris and D. microps, and between D. microps and P. maniculatus, and a negative association between P. longimembris and P. maniculatus. A species cluster dendogram with respect to sites in common further supports the interspecific association results. A site cluster dendogram with respect to species abundances implies that dune habitat promotes diversity but not uniformity. All results indicate that M. megacephalus is more abundant and stable at sites with high species richness. The results also provide evidence for the existence of assembly rules, competition, and niche partitioning in desert rodent communities.

Biocrusts and the ecosystem services they provide are becoming more susceptible to fire as exotic annual grass invasions facilitate the spread of desert wildfires. Further, precipitation patterns across the western United States are predicted to change over the next century, and have the potential to dramatically influence fire regimes and the recovery of burned biocrusts. Despite these changes to desert fire and precipitation cycles, our understanding of post-fire biocrust recovery is limited, especially regarding the first two years after fire. To investigate biocrust recovery, we created burn manipulations (i.e., unburned and burned) and tracked crust form and function over two years in one cold and one hot desert ecosystem (UT, USA). We evaluated the entire bacterial community, but focused on Cyanobacteria species that confer soil stability and N fixation capabilities to biocrusts. Specifically, we quantified shifts in biocrust bacterial community composition using target metagenomics of 16S rDNA; monitored biocrust moss and lichen cover; measured N fixation potential; and assessed soil infiltration rates and soil stability. We found little evidence that biocrust form or function recovered from fire within two years. Based on pyrosequencing results, fire altered biocrust community composition in interspace and shrub biocrusts. Cyanobacteria species were almost completely eliminated by fire, constituting 9-21% of unburned plots and less than 0.01% of burned interspace and shrub biocrust communities. Based on cover estimates, no lichen or moss species survived the fire or recovered within two years. N fixation potentials decreased by at least six-fold in burned interspace biocrusts, representing a reduction in soil N inputs into already N-limited desert soils. Soil infiltration rates also drastically declined in burned biocrusts and remained depressed, but only remained depressed for one year. To investigate the interactions between biocrust recovery, fire, and precipitation, we nested precipitation treatments manipulating the amount of monthly rainfall (i.e., ambient, plus 30% and minus 30%) within burn treatments during the second year. Soil NH4+ was the only parameter to be affected by precipitation, and exhibited a positive relationship with precipitation magnitude at the end of one year. Our results demonstrate that fire is a strong destabilizer of the bacterial components of biocrust communities and that the ecosystem services provided by crusts recover at different rates, with N dynamics recovering more slowly than soil ecohydrology.

Understanding the impacts of climate change is critical for improving the conservation and management of ecosystems worldwide. Ecosystems vary along a precipitation and temperature gradient, ranging from tropical jungles to arid deserts. The Great Basin is a semi-arid eco-region that is found within the western United States. Plant communities within the Great Basin range from sagebrush valleys to sub-alpine conifer forests found at high elevation areas. It is predicted that the Great Basin will experience prolonged periods of drought, more intense fires, and greater variability in average annual and monthly precipitation, all in response to changes in climate patterns. At the lower elevations, sagebrush communities are expected to experience less suitable habitat conditions, however, less is understood about vegetation response at upper elevations. Understanding forest composition and structure at these upper elevations within the Great Basin will help us better understand potential impacts from climate change. In chapter 1, we characterized Pinus longaeva (Great Basin bristlecone pine D.K. Bailey) forest structure and composition. We mapped this tree species distribution and characterized forest structure and composition using a sampling protocol that included both biophysical variables and individual tree characteristics. We collected data from 69 mixed and homogenous P. longaeva stands found within the Great Basin and Colorado Plateau. Results suggest that P. longaeva forest structure and composition exhibit high structural variability in tree characteristic measurements like density, basal area, growth rate, age, and in biophysical variables such as substrate type, slope, aspect, elevation, average monthly temperature and precipitation, latitude, and longitude. This study also found that variability in forest composition and structure in P. longaeva forests allows for greater flexibility in the breadth of life-history strategies and probable resiliency to climate change. In chapter 2 we used remote sensing images with high spatial resolution to identify 685 unique P. longaeva stands on 42 mountain ranges. Pinus longaeva was found on the White Mountains on the western edge of the Great Basin to the Colorado Plateau's Henry Mountain and West Tavaputs Plateau in the East, and from the Spring Mountains in the South to the Ruby and Spruce Mountains in the North. Stands covered 113,886 ha across the geographic distribution. A comparison between our maps and those produced by David Charlet found a total of 36% overlap of P. longaeva. We mapped 58 unique stands that the control dataset lacked and 11 stands that we did not include. We believe that this is the most comprehensive P. longaeva distribution map created to date.