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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    A GOOD NEIGHBORHOOD TO RAISE A BROOD: TREE SPECIES DIVERSITY DECREASES PERIODICAL CICADA OVIPOSITION AND TREE RESPONSE
    (2023) Jayd, Kristin; Burghardt, Karin; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Natural systems contain diverse assemblages of plants, providing a matrix of potential hosts that herbivores must navigate. Insect-plant host choice patterns are crucial to understanding both herbivore outbreaks and the consequences of outbreaks for plant hosts. Here, I follow the 2021 Brood X periodical cicada mass emergence event in the BiodiversiTREE forest diversity experiment at the Smithsonian Environmental Research Center (SERC) in Edgewater, MD, to uncover whether tree diversity influences cicada oviposition preferences or tree responses to oviposition (flagging), for 15 tree species grown in plots of single species or 12-species mixtures. While cicadas demonstrate clear tree species preferences, the diversity of the surrounding tree neighborhood plays at least as important a role in determining oviposition preference and tree flagging responses. Cicadas were threefold more likely to oviposit in trees grown in single species vs. mixed species plots. While overall, I find a concomitant decrease in tree flagging in diverse plots. I also document that species flag at different rates in response to the same oviposition scar density. Even when accounting for differential oviposition rates, surrounding tree diversity remains an essential additional predictor of tree flagging responses with trees in diverse plots less likely to flag at the same density of scars, suggesting a differential capacity of trees to tolerate damage when growing in single species plots. This study creates a richer understanding of the importance of tree context, specifically surrounding tree diversity, in shaping the ecological ramifications of a mass insect emergence event.
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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.