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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Item Ecological Restoration Drives Functional Composition and Diversity in Urban Forest Patches(2020) Do, Sara Miya; Johnson, Lea R; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Urbanization greatly alters environmental conditions, affecting biodiversity in cities and ecological processes. To restore processes and native biodiversity, land managers have turned to ecological restoration of urban forest patches. Urban forest patches, nested within urban ecosystems, are subject to urban influences during ecological succession. Building on a long-term study evaluating outcomes of ecological restoration in New York City, I examined the effects of urban conditions, restoration, and forest succession on functional composition and diversity of restored and unrestored urban forest patches after 15-20 years. Functional traits play an essential role in community assemblages and influence the resilience and ecosystem functioning of urban ecosystems. I found that restored plots had greater functional evenness. Differences in functional composition indicated direct influence from restoration, succession, urban conditions, and success in meeting restoration goals. These results demonstrate that ecological restoration drives changes in functional composition and diversity of urban forest patches.Item A BIODEGRADABLE POT TECHNIQUE, AND EMERGY ANALYSIS TO IMPROVE RESTORATION OUTCOMES OF POTAMOGETON PERFOLIATUS L.(2018) Zinecker, Elizabeth Kirsten; Kangas, P. C.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Potamogeton perfoliatus (L.) (P. perfoliatus), is a species of submersed aquatic vegetation (SAV) in mesohaline Chesapeake Bay that provides important ecosystem services but has been in decline. Efforts to restore its populations have met with mixed success. While the challenges to healthy SAV growth such as inadequate light for photosynthesis, poor water quality, and site disturbance have been well documented, studies using microcosms have failed to specifically examine other factors such as propagule type and seed storage duration, source population, plant growth response to a fully characterized substrate, and planting techniques, for the duration of an entire simulated growing season. Also, no studies have conducted an environmental cost accounting to assess the sustainability of a given restoration approach. This research investigated the growth and reproductive responses of P. perfoliatus propagules to various substrates and planting techniques; and conducted an emergy analysis case study, a type of environmental cost accounting, to compare two restoration techniques. P. perfoliatus net primary productivity and reproductive potential was highest when grown in sediment cores taken from SAV beds (~1.0gDW/m2/day, 18% stems with inflorescences), with peat/oyster shell being the next most desirable substrate choice for propagation (~0.86 gDW/m2/day, 4% stems with inflorescences). Seeds grown in biodegradable pots grew no differently than seeds grown in control polyethylene pots, or seeds planted by hand onto the bare sediment surface of the microcosm, (although hand-planting required multiple attempts to keep buoyant, germinated seeds in place). Seeds grown from harvests four years apart also showed no differences in yield (~0.56 gDW/m2/day). Biodegradable pots lost on average 60 percent of their mass over 12 weeks, and degraded more in brackish vs. fresh SAV bed sediments in the field. Emergy analysis indicated that planting seed-filled biodegradable pots resulted in 97% more area (m2) SAV bed restored than hand transplanting sods, and was more ecologically sustainable. These results indicate that appropriate substrates for propagation and restoration sites, and the ability to securely place propagules in the sediment, may be critical to P. perfoliatus establishment and success, thereby enhancing SAV habitat in Chesapeake Bay.Item NATURAL SELECTION, POPULATION GENETICS, AND TRAIT DIVERSIFICATION OF SILENE STELLATA AND ITS POLLINATING SEED PREDATOR HADENA ECTYPA(2017) Zhou, Juannan; Dudash, Michele R; Fenster, Charles B; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)My dissertation explores four aspects of the interaction system consisting of the hermaphroditic plant Silene stellata and its pollinating seed predator Hadena ectypa in a community context. My overarching goal is to deepen our understanding of the selection dynamics influencing floral evolution of hermaphroditic plants. First, I characterized the mating system of S. stellata to evaluate its role on floral evolution of S. stellata and the Silene-Hadena interaction. Second, I compared the spatial genetic structures of S. stellata and H. ectypa to evaluate any discrepancy in their dispersal abilities. Third, I addressed whether selection pressures on floral traits of S. stellata differ between sexual functions and between pollinator types. Last, I quantified the genetic basis of the Silene floral traits to predict evolutionary response under complex selection scenarios. In Chapter 1, I found the study S. stellata population to be predominantly outcrossing with short pollen dispersal distance. The lack of effect of pollinator types (specialized seed predator and other nocturnal copollinating moths) on S. stellata mating system parameters suggests that the dual pollinator type relationship with S. stellata is stable and perhaps contributes to the persistence of the plant species. In Chapter 2, I found no genetic differentiation among the Hadena populations, while the Silene populations showed strong spatial structure. This suggests that pollen flow between Silene populations rarely co-occurs with moth movement. This asynchrony in gene flow could potentially stabilize the interaction dynamics and prevent strict local coadaptation. In Chapter 3, I found conflicting selection pressures between male and female reproductive functions of S. stellata. Strong selection through female function was detected to avoid fruit predation, while competition for mates through male function provides a counterbalancing force potentially contributing to the long-term maintenance of this interaction. In Chapter 4, I found intermediate heritability and prevalent positive genetic correlations between Silene floral traits, suggesting the Silene population is capable of responding to phenotypic selection on its floral design, while the abundant genetic correlations could also pose certain constraints on trait divergence. My results suggest that floral evolution is governed by complex, interdependent processes and that the Silene-Hadena interaction could be maintained through the dynamical balance between various opposing evolutionary forces.Item EVALUATING THE EFFECTS OF POLLINATOR MEDIATED SELECTION ON PATTERNS OF FLORAL VARIATION(2016) Diller, Carolina; Fenster, Charles B; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Angiosperm flowers astonish for their high morphological diversity. More importantly, flower shape variation has a significant reproductive and evolutionary role. Here, I studied the relationship between flower shape and pollination precision, i.e. the precise transfer of pollen across flowers by pollinators. In the first two chapters, I studied the role of one floral trait, corolla chirality, in three species of Hypericum (Hypericaceae). Unfixed corolla chirality is the presence of pinwheel arrangement of petals, both right and left rotated, within an individual. Specifically, I evaluated whether corolla chirality promotes disassortative mating between flower morphs through directed movement of pollen and pollinators between flowers. This precise pollination mechanism could increase outcrossing rates by reducing geitonogamous pollinations. Nevertheless, pollinators were indifferent to corolla chirality and thus pollination for unfixed corolla chirality is similar to radially symmetric flowers with a generalized (non-precise) pollination system. In chapter 3, I performed a macroevolutionary analysis on multiple key flower traits. I hypothesized that flower traits with precise pollinations due to precise fit with their pollinators or due to increased pollination specialization will be under uniform directional selective pressures and thus be less variable than flowers with less precise pollination system. I found that flowers with lateral orientation or bilateral symmetry were significantly less variable than their alternative states (vertical and radial, respectively). Thus, I demonstrate that traits that restrict pollinator landing and movement play an important role in pollination precision. In chapter 4, I quantified patterns of genetic variation available for pollination precision to evolve in a male reproductive trait (i.e. stamen height) using fast-cycling Brassica rapa. The match of anthers and stigmas to the contact area on the pollinator body conveys precise pollen transfer. My results suggest that individual mean stamen height can evolve to match the population mean pistil height (presence of additive genetic variation), but that some level of imprecision will remain due to lack of additive genetic variation for within-individual stamen height variation. In summary, floral traits vary in their role in pollination precision and the evolution of pollination precision may be constrained by the types and amounts of genetic variation.Item Using a Combination of Phylogenetic Comparative and Paleobotanical Methods to Elucidate Patterns of Lineage Selection in Rosales (Plantae: Anthophyta)(2016) Simpson, Andrew Gordon; Fenster, Charles B.; Wing, Scott L.; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)An increasing focus in evolutionary biology is on the interplay between mesoscale ecological and evolutionary processes such as population demographics, habitat tolerance, and especially geographic distribution, as potential drivers responsible for patterns of diversification and extinction over geologic time. However, few studies to date connect organismal processes such as survival and reproduction through mesoscale patterns to long-term macroevolutionary trends. In my dissertation, I investigate how mechanism of seed dispersal, mediated through geographic range size, influences diversification rates in the Rosales (Plantae: Anthophyta). In my first chapter, I validate the phylogenetic comparative methods that I use in my second and third chapters. Available state speciation and extinction (SSE) models assumptions about evolution known to be false through fossil data. I show, however, that as long as net diversification rates remain positive – a condition likely true for the Rosales – these violations of SSE’s assumptions do not cause significantly biased results. With SSE methods validated, my second chapter reconstructs three associations that appear to increase diversification rate for Rosalean genera: (1) herbaceous habit; (2) a three-way interaction combining animal dispersal, high within-genus species richness, and geographic range on multiple continents; (3) a four-way interaction combining woody habit with the other three characteristics of (2). I suggest that the three- and four-way interactions represent colonization ability and resulting extinction resistance in the face of late Cenozoic climate change; however, there are other possibilities as well that I hope to investigate in future research. My third chapter reconstructs the phylogeographic history of the Rosales using both non-fossil-assisted SSE methods as well as fossil-informed traditional phylogeographic analysis. Ancestral state reconstructions indicate that the Rosaceae diversified in North America while the other Rosalean families diversified elsewhere, possibly in Eurasia. SSE is able to successfully identify groups of genera that were likely to have been ancestrally widespread, but has poorer taxonomic resolution than methods that use fossil data. In conclusion, these chapters together suggest several potential causal links between organismal, mesoscale, and geologic scale processes, but further work will be needed to test the hypotheses that I raise here.Item A study of the effect of certain factors on the size and composition of apples and the effect of fruiting on bud differentiation(1931) Haller, M. H.; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)Item A study of the factors influencing the red color on apples(1930) Fletcher, Lewis Arrowood; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)Item Sex expression in cucumbers(1933) Edmond, J. B.; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)Item A biochemical and physiological study of the insoluble pectic materials in vegetables and fruits(1925) Conrad, Carl Marcus; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)Item The relation of protoplasmic streaming in the Avena coleoptile to respiration and auxin transport(1939) Olson, Rodney Andreen; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)