Theses and Dissertations from UMD

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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 give thesis/dissertation in DRUM

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

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    Plant-insect interactions in a shifting coastal ecosystem: Avicennia germinans and its associated arthropods
    (2020) Nathan, Mayda; Gruner, Daniel S; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The climate’s role in determining where species occur is increasingly well understood, but our ability to predict how biotic interactions both influence and respond to species’ range shifts remains poor. This is particularly important when considering climate-change-driven range shifts in habitat-forming species like mangroves, given their impact on ecosystem structure and function. In this dissertation, I consider the arthropods associated with the black mangrove, Avicennia germinans, to explore whether patterns of arthropod diversity affect the rate of a plant’s range expansion, and, in turn, how a range-expanding plant alters arthropod communities in habitats where it is invading. Among arthropods with the potential to influence plants’ range dynamics, pollinators can directly affect plant reproduction and ability to spread into new territory. Breeding system experiments reveal that A. germinans relies on pollinators for full fruit set, and surveys along the Florida coast show a substantial northward decline in the overall frequency of pollinator visits to A. germinans flowers. However, the decline in abundance of some common pollinator taxa is partly offset by an increase in the frequency of other highly effective taxa. Furthermore, range-edge A. germinans produce more flowers than southern individuals, contributing to high range-edge fecundity and enabling range expansion. As a woody plant with nectar-producing flowers, A. germinans is a novel resource for arthropods in the salt marshes where it is encroaching. To understand arthropod community assembly on these frontier mangroves, and how mangrove presence affects marsh arthropod community composition, I compare arthropod communities in these adjacent vegetation types. Arthropods form distinct communities on mangroves and marsh vegetation, with at least one A. germinans specialist already present in this range-edge population. However, neither mangrove proximity nor the abundance of mangrove flowers appears to influence salt marsh arthropod community structure, indicating that mangrove encroachment may lead to a net increase in arthropod diversity in coastal regions by increasing habitat heterogeneity. In sum, plants that rely on pollinators can avoid range-edge reproductive failure by attracting a diverse group of pollinating taxa, and range-expanding plants can rapidly alter invaded communities by shaping diversity at very local scales.
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    Nutrient enrichment effects on mangrove sediments from differing tree height zones in Bocas del Toro, Panama
    (2008-01-28) Borgatti, Aimee Rachel; O'Neil, Judith M; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Red mangrove (Rhizophora mangle L.) forests have distinct tree-height zones, with tall trees fringing the ocean and shorter trees in interior stands. A long-term nitrogen (N) and phosphorus (P) fertilization experiment in Almirante Bay, Bocas del Toro Province, Panama has shown that tree-height zonation is primarily related to nutrient limitation. This experiment was used to test the effects of in-situ nutrient additions and tree zonation on mangrove sediments. The sediments underlying the experimental R. mangle trees were sampled and N2 fixation, 15N, chlorophyll a, percent N and P, and percent organic biomass were quantified. Both N and P additions significantly affected almost every parameter measured in both zones within this experiment. These results are likely to have implications for management since N and P inputs are predicted to increase throughout the tropics and subtropics worldwide.
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    ASSESSMENT OF MANGROVE AND SALT MARSH MESOCOSM FUNCTIONAL VALUE USING PERIWINKLE SNAILS, LITTORARIA ANGULIFERA AND LITTORARIA IRRORATA, AS AN INDICATOR
    (2004-04-01) Swartwood, Stacy Lyn; Kangas, Patrick C; Marine-Estuarine-Environmental Sciences
    Although much research has been conducted on restoration techniques, questions about the functional value of restored and constructed ecosystems remain. Gastropods are a particularly useful indicator organism because they play a vital role at the detrital interface. This study addresses the question of whether the age structure, population density, and distribution of Littoraria angulifera in the Smithsonian Institution's Florida Everglades mesocosm in Washington, DC is analogous to that of wild populations. The second phase investigates these same factors, in populations of Littoraria irrorata at a reference site on Slaughter Creek and six mesocosm replicates at Horn Point Laboratory in Cambridge, Maryland. Neither the mangrove nor the salt marsh mesocosms were able to support healthy, reproducing populations of periwinkle snails. Salinity, humidity, territory requirements, habitat complexity, precipitation, photoperiod, and tidal variation were identified as potential causal factors for mortality and the absence of evidence of juvenile recruitment to mesocosm populations.