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

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Subject: search.filters.subject.plant-insect interactions

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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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    QUANTIFYING CONTEXT-DEPENDENT OUTCOMES OF THE INTERACTION BETWEEN SILENE STELLATA (CARYOPHYLLACEAE) AND ITS POLLINATING SEED PREDATOR, HADENA ECTYPA (NOCTUIDAE), A POTENTIAL MUTUALIST
    (2012) Kula, Abigail Rogers; Dudash, Michele R; Fenster, Charles B; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Interactions with variable outcomes are particularly useful in allowing for the exploration of ecological conditions that give rise to and allow persistence of mutualistic interactions. Understanding the context and conditions under which outcomes of mutualistic interactions vary is critical to understanding their ecology. Of insect-plant mutualisms, pollination by pollinating seed predators is a unique interaction in which flowers and fruits are food for the pollinator's young, and outcomes range from obligate (e.g., figs-fig wasps) to facultative (e.g., Silene-Hadena). The facultative nature of Silene-Hadena interactions makes them ideal for a study of the role of ecological conditions in determining interaction outcomes and consequently may inform us of the conditions promoting mutualisms. My goals were to explore variation in the interaction outcome between Silene stellata and its pollinating seed predator, Hadena ectypa, under different ecological conditions and, in addition, to understand the role of plant traits in attracting oviposition and the role of oviposition in determining interaction outcomes. My research demonstrates that plants with longer corolla tubes had higher oviposition rates in each year, and I observed significant positive relationships between oviposition and predation and oviposition and fruit initiation. Further, this interaction is antagonistic for spatially isolated plants because low pollination levels of isolated plants resulted in lowered seed set compared with non-isolated plants, and predation was significantly higher for isolated plants. Finally, the magnitude of phenological synchrony between S. stellata flowering and H. ectypa oviposition and the effect of synchrony on flower and fruit predation varied between seasons. This interannual variability in the effect of synchrony on predation may be attributed to significant differences in within season patterns of flowering and oviposition. My research demonstrates a link between oviposition and host plant traits, the role of oviposition in host plant reproduction and the identification of two ecological scenarios under which the interaction outcomes between S. stellata and H. ectypa vary. This variation under different ecological scenarios, along with positive relationships between oviposition and both predation and fruit initiation, demonstrates a mechanism for the persistence of this interaction and other facultative pollinating seed predator interactions.
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    Nutrient limitation and its consequences for performance and the homeostatic regulation of macronutrient composition in two phytophagous insects with divergent life-history strategies
    (2005-01-13) Huberty, Andrea; Denno, Robert F; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Insect herbivores have a decidedly higher nitrogen and phosphorus than their host plants, an elemental mismatch that places severe constraints on their ability to meet nutritional demands. This study examined the consequences of macronutrient (nitrogen and phosphorus) limitation for two wing-dimorphic, phloem-feeding planthoppers with very different life-history strategies: the sedentary <i>Prokelisia dolus</i> and the migratory <i>P. marginata</i>. As a consequence of the constraints dispersal imposes on ingestion capacity, I argue that species using dispersal as a strategy for acquiring limiting nutrients are unable to adequately obtain nutrients when dispersal is not an option. The effect of nitrogen and phosphorus limitation for planthopper performance (Chapter 1) and homeostatic regulation of macronutrient composition (Chapter 2) were determined, as were the constraints dispersal places on other traits (ingestion capability) used to cope with nutrient limitation (Chapter 3). The planthopper species responded differently to nutrient limitation. The survival, body size, and development rate of both species was adversely affected on nutrient-deficient host plants, but <i>P. marginata</i> was more negatively affected than <i>P. dolus</i>. Nitrogen was more limiting than phosphorus for both species. <i>Prokelisia marginata</i> was also less able to regulate its macronutrient composition (C:N:P) and incurred greater growth penalties than <i>P. dolus</i>. Overall, the migratory species was far more sensitive to nutrient limitation. Divergent life-history strategies (migratory versus sedentary) and the differential muscle allocation patterns associated with such strategies provide the mechanism underlying the consistently different performance responses of the two planthopper species on nutrient-deficient host plants. Morphometric and gravimetric measures of investment in flight versus feeding indicate that the sedentary <i>P. dolus</i> allocates more muscle mass to feeding whereas <i>P. marginata</i> invests more heavily in flight. Due to its greater investment in feeding musculature and associated enhanced ingestion rate, the immobile <i>P. dolus</i> is better equipped to meet macronutrient demands when faced with nutrient-poor food than the migratory <i>P. marginata</i>. Results of this research demonstrate the importance of considering life-history strategies, and associated constraints imposed on ingestion, when assessing how the macronutrient stoichiometry of plants (C:N:P content) interfaces with the nutritional requirements of phytophagous insects to affect their growth and performance.