Theses and Dissertations from UMD
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Item NOVEL APPROACHES TO STUDYING BIODIVERSITY IN REMOTE AREAS: DISTRIBUTION OF LICHENS AND PENGUINS ACROSS THE ANTARCTIC PENINSULA(2013) Casanovas, Paula Victoria; Fagan, William F; Lynch, Heather J; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Biodiversity inventories are a critical resource, providing baseline information for assessing environmental changes over time. In many cases, the underlying datasets are generated by "opportunistic" sampling efforts or they are consolidated from diverse datasets collected for different purposes. These datasets are typically patchy and incomplete, requiring the use of sophisticated statistical analyses. The Antarctic Peninsula (AP) is one of those areas where direct observation of species distribution is difficult; it is also an area that in recent decades has been experiencing important environmental changes, which influence population and ecosystem dynamics. I addressed biogeographical questions in the AP archipelago, using remote sensing and opportunistic data sets for two very different groups of organisms: lichens and penguins. Although taxonomically different, both groups are key components of the AP terrestrial ecosystem, and share the need to couple biodiversity surveys with modeling to understand species distribution and abundance patterns in large areas of remote wilderness. The results of this dissertation work are interesting to polar biologists, because evidence suggests that the input of nutrients by seabirds can significantly impact floral diversity and abundance in nutrient-poor polar communities. The datasets and protocols for data collection and analyses generated in this project are valuable in themselves for the scientific community. They could be used as the basis for a valuable and practicable monitoring program and procedures for the evaluation of the data derived from it. In the Antarctic Peninsula in particular, this information will aid in the delineation and management of protected areas, as well as in the evaluation of the impacts of climate change and human visitation to the most traveled locations. Furthermore, this research provided an example of how an approach that integrates the use of existing remote-sensing products with independent ongoing field sampling efforts, "citizen scientist" data collection, and historical datasets can yield low-cost, high-benefit studies that can be useful both to understand how species respond to their environment, and to help environmental managers to predict and cope with imminent changes due to global warming.Item Linking detritus and primary producer based communities(2008-03-25) Hines, Jessica; Denno, Robert F; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Terrestrial food-web theory has been developed largely by examining species interactions in primary producer food webs. However, the decomposer subsystem can have strong influences on aboveground communities and ecosystem functioning. Here I examine, at several spatial scales, the complexity of terrestrial food-web interactions by considering interactions between species in detritivore and primary-producer food webs. I focused on Spartina alterniflora marshes and interactions among the numerically dominant herbivore Prokelisia dolus, its major spider predator Pardosa littoralis, and several detritivores (Littorophiloscia vittata, Orchestia grillus, Melampus bidentatus and Littoraria irrorata). I found that predator-detritivore interactions have weak indirect effects on plant growth and decomposition (Chapter 1). Furthermore, by serving as alternative prey, detritivores can influence the strength of predator-herbivore interactions. However, the strength of predator-herbivore-detritivore interactions was species-specific and depended on habitat structure (leaf litter - Chapter 1) and detritivore identity (Chapter 2). Although detritivore species are often functionally redundant in soil communities, changes in detritivore species composition can have divergent influences on aboveground predator-herbivore interactions (Chapter 2). Whereas some detritivores (Littorophiloscia vittatta) promote herbivore and predator survival, other detritivores (Littoraria irroratta) reduce predator and herbivore densities. Moreover, the geographic distribution of detritivores influences the relative strength of predator-herbivore interactions across broader spatial scales (Chapter 3). I found a shift in the relative abundance of dominant detritivore, herbivore, and predator species across a 1660 km latitudinal gradient. Detritivorous Littoraria snails that abound on low-latitude marshes modify Spartina vegetation structure and create an unfavorable habitat for Pardosa spiders. Pardosa exert stronger predation pressure on Prokelisia planthoppers on high-latitude marshes where spiders are abundant. Changes in global carbon cycles may influence the strength of linkages between primary production and decomposition food webs. I examined how changes in the detritivore food chain influenced the growth of two plant species (Scirpus olneyi and Spartina patens) under elevated and ambient CO2 conditions. I found limited and species-specific support for the increased importance of the decomposition pathway under elevated CO2 conditions. Overall, detritivores modified predator-herbivore interactions, live plant growth, and decomposition. The strength of these interactions changed with the composition of the detritivore community, latitude, and atmospheric CO2 conditions.Item Correlates of Terrestrial Vertebrate Species Richness: an Evaluation of Environmental Hypotheses over the Western Continental USA(2006-04-24) Slayback, Daniel Andrew; Prince, Stephen D; Geography; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)An explanation for the unequal distribution of life forms across the Earth's surface has been a persistent and problematic question in modern ecology ever since these patterns were first noted, over 100 years ago. Most empirical research supports one of three environmental hypotheses to explain these patterns: environmental energy (ambient environmental energy or ecosystem productivity); climatic variability; or habitat heterogeneity. This research examines these hypotheses using better datasets than those commonly considered, and using a consistent methodology that addresses often neglected statistical and analytic details. The environmental datasets used in this study are derived from time series of satellite and ground station data, including the Daymet climate data, and net primary productivity data from the GLOPEM model. Species richness is derived from the individually modeled vertebrate distributions provided by the individual state Gap Analysis Projects for the western US states of California, Oregon, Washington, Idaho, Montana, Wyoming, Utah, and Colorado, which define the spatial extent of this study. The study methodology relies upon the summary of results from many model variants for each hypothesis. These variants are constructed by creating regression models at each of four different spatial scales (8, 16, 32, and 64 km grid cells), for each class of vertebrates (amphibians, birds, mammals, reptiles, and all), and over each of the eight states considered. Preliminary studies found that ordinary least squares would be a sufficient model form, although conditional autoregressive models were extensively considered. Other preliminary work examined issues of spatial autocorrelation and variable selection. The results indicate that the energy/productivity hypothesis consistently outperforms all other hypotheses in explaining species richness, across almost all spatial scales, geographic regions, and vertebrate classes. The performance of the climatic variability and habitat heterogeneity hypotheses varies for particular states or vertebrate classes. Vertebrate data quality was important; results for Colorado and Washington were frequently unusual, suggesting an incompatibility between their modeled vertebrate distributions and those of other states. Models of reptile richness also often showed substantially different characteristics than those for other vertebrates. Overall the results provide additional support to the energy/productivity hypothesis, from a more comprehensive methodological basis.