UMD Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/3

New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.

More information is available at Theses and Dissertations at University of Maryland Libraries.

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    EFFECTS OF THE INVASIVE PHRAGMITES AUSTRALIS ON THE PREDATION OF MOSQUITOES THROUGH CHANGES IN HABITAT COMPLEXITY
    (2019) Weeks, Virginia Lynn; Leisnham, Paul; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Ephemeral stormwater ponds in the eastern United States are often invaded by non-native Phragmites australis which has been associated with numerous negative impacts on resident systems, including changes in hydrology, displacement of native macrophytes, and degradation of wildlife habitat. Few studies have documented the impacts of invasive P.australis on macroinvertebrate communities. Vegetated edges of stormwater retention facilities are often important developmental habitat for medically significant mosquitoes and the invertebrate predators that regulate their abundances. The displacement of resident macrophytes by P.australis could alter the physical structure of pond vegetation and disrupt the interactions between mosquitoes and their visual predators. The overall goal of my thesis was to evaluate differences in habitat complexity between native macrophytes, T.latifolia and J.effuses, and P.australis, and explore how those differences may impact predation of mosquitoes. I addressed this goal by conducting a controlled laboratory predation experiment and field surveys of four stormwater ponds.
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    CRITICAL PATCH SIZES AND THE SPATIAL STRUCTURE OF SALT MARSH COMMUNITIES
    (2009) Martinson, Holly Marie; Fagan, William F; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The size, connectivity, and quality of habitat patches can have multifaceted impacts on species and communities. In this dissertation, I combined a multi-year field survey, manipulative field experiments, and a literature review to investigate how spatial structure influences species and their trophic interactions in fragmented habitats. For all empirical work, I used as a study system the arthropod assemblage found on patches of the salt marsh grass Spartina patens. In Chapter 1, I conducted seven surveys of habitat patches over three years to examine the effects of patch size, connectivity, and local environmental conditions on a guild of specialist sap-feeding herbivorous insects and their natural enemies. I found striking differences among species in the effects of both patch size and connectivity, which led to differences in species' relative abundances and trophic structure among these patches. In Chapter 2, I manipulated host plant quality and predator density to experimentally examine mechanisms that might structure this arthropod community. I found that positive responses of herbivores to experimentally-elevated patch quality were limited by dispersal constraints and that predation by abundant generalist spiders may constrain the spatial distribution of certain species. Investigating systems beyond the marsh, I conducted a literature review and analysis in Chapter 3 wherein I examined whether the spatial structure of habitats generally influences trophic interactions. From the literature, I identified 171 studies of trophic interactions in fragmented habitats and found that the influence of fragmentation and related variables on the occurrence or strength of trophic interactions was largely predictable based on the habitat affinity of interacting species. With this dataset, I also identified key gaps in the fragmentation literature, including a heavy bias towards the study of two-species interactions. Therefore, in Chapter 4 I took advantage of my data from the salt marsh to identify how, in addition to the two-species interactions of parasitism and egg predation, more complex food web interactions might depend on variation in the size of habitat patches. Overall, my findings show that variation in patch size can have varied, but predictable, effects on patch occupancy, population density, and interactions between species in fragmented habitats.
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    Predation by eastern mudminnows (Umbra pygmaea) on macroinvertebrates of temporary wetlands
    (2009) Lombardi, Susan Elizabeth; Lamp, William O.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Fish play a substantial role in aquatic food webs, yet the effect of feeding activities of small stream fish that enter seasonally-flooded temporary wetlands during periods of hydrologic connectivity is not well understood. In this study, eastern mudminnows (Umbra pygmaea) were introduced to a fishless wetland in Caroline County, Maryland, and the aquatic macroinvertebrate community did not significantly change within two weeks. Gut contents of mudminnows collected from the wetland and a stream consisted primarily of dipteran larvae; ostracods were also a common food source for wetland mudminnows. Common prey not found in gut contents but present in the wetland were tested as food, and all taxa were consumed in a no-choice predation experiment. Mudminnows have the potential to directly affect multiple trophic levels and subsequent ecosystem functioning through predatory interactions with sustained hydrologic connectivity between fish sources and temporary wetlands.
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    PREDATOR INFLUENCE ON GOLDEN LION TAMARIN NEST CHOICE AND PRESLEEP BEHAVIOR
    (2004-04-27) Franklin, Samuel Patrick; Dietz, James M; Behavior, Ecology, Evolution and Systematics
    Primate sleeping site choices and cryptic pre-retirement behaviors presumably aid survival by reducing a predator's ability to find and access prey. I examined presleep behaviors in a population of golden lion tamarins (Leontopithecus rosalia) that recently suffered heavy losses from predators. I analyzed existing sleeping site data to determine whether groups at higher risk of predation, as measured by the number of observed encounters with potential predators, changed den sites more frequently than groups at lower risk. Additionally, I evaluated scent marking data to resolve whether study individuals decreased scent marking just prior to retiring. The predator encounter interval was not a significant predictor of the rate with which social groups changed den sites and study individuals significantly increased scent marking just prior to retiring. Consequently, it appears that after multiple generations without exposure to heavy predation pressure the tamarins in this isolated population fail to alter their behavior appropriately to mitigate predation risk.