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 The Ecological Velocity of Climate Change(2020) O'Leary, Donal Sean; Hurtt, George C; Geography; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Vegetation productivity and distributions are largely driven by climate, and increasing variability in seasonal and interannual climate is both changing the spatiotemporal patterns of resource availability across the landscape, and driving species’ migrations towards climate refugia. Climate and vegetation dynamics take place along the time dimension (e.g. earlier snowmelt and arrival of spring in temperate mountains), but they also occur throughout space, where changes in climate can be expressed as a movement across the landscape (e.g. warm temperatures and migratory animals moving uphill in spring, or tree species distributions moving uphill and towards the poles under climate change). Here, we present new methods to track the movement of climate and vegetation, quantifying the ecological velocity of climate change at the landscape scale. Our focus is on national parks of the USA, which are important study areas because of their great conservation and social value, protection from anthropogenic disturbances, and longstanding research and monitoring records. First, we explore the spatio-temporal relationships between snowmelt timing and vegetation phenology in Crater Lake National Park. We find that snowmelt timing is closely linked to spring greenup, but has far weaker influence on later season phenology, such as the senescence or growing season length. Second, we extend our comparison of snowmelt timing with vegetation phenology across space and time together as we track the speed and direction of receding seasonal snowpack (snowmelt velocity) with the ‘green wave velocity’ of spring greenness that follows. We find that snowmelt velocity has a moderate predictive power for green wave velocity in areas with steep slopes, where both phenomena are controlled by strong spatial gradients relating to elevation. Third, we extend our analysis into the future as we forecast the climate velocity of air temperature and precipitation in and surrounding national parks from 2019-2099. Here, we identify possible corridors and velocities of future climate migration across park boundaries, highlighting locations of ecological concern and climate vulnerability. Taken together, our analysis of the ecological velocity of climate change forms new connections among climate, conservation, and spatial sciences while prioritizing management-relevant deliverables.Item USING AN INDIVIDUAL BASED MODEL TO EVALUATE THE EFFECTS OF CLIMATE CHANGE ON THE REPRODUCTIVE PHENOLOGY OF EELGRASS (ZOSTERA MARINA L.) ALONG A LATITUDINAL GRADIENT(2017) Foley, Jessica Lynn; Harris, Lora A; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)I explored the effects of climate change on the reproductive biology of the clonal marine angiosperm Zostera marina L. (eelgrass) using an individual-based model. The model captures whole plant ontogeny, morphology, and ecophysiology from seed to reproductive adult to simulate the plasticity of eelgrass in response to environmental variables. Using a latitudinal gradient as a proxy for climate change, virtual seeding experiments were performed in three locations along the East coast of the United States. I simulated the impacts of increased temperatures on Z. marina’s biomass, reproductive phenology, and life history. Warmer temperatures resulted in a modeled decrease of Z. marina’s total biomass, as well as altered reproductive timing and strategy. These results have implications for long term predictions of Z. marina persistence in its traditional biogeographic range, and indicate adaptation via shifts in phenology and reproductive strategy may interact to dampen some negative consequences of increased temperatures.Item Assessing the influence of abiotic factors and leaf-level properties on the stability of growing-season canopy greenness in a deciduous forest(2016) Cunningham, Vanessa M.; Nelson, David M; Elmore, Andrew J; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Maps depicting spatial pattern in the stability of summer greenness could advance understanding of how forest ecosystems will respond to global changes such as a longer growing season. Declining summer greenness, or “greendown”, is spectrally related to declining near-infrared reflectance and is observed in most remote sensing time series to begin shortly after peak greenness at the end of spring and extend until the beginning of leaf coloration in autumn,. Understanding spatial patterns in the strength of greendown has recently become possible with the advancement of Landsat phenology products, which show that greendown patterns vary at scales appropriate for linking these patterns to proposed environmental forcing factors. This study tested two non-mutually exclusive hypotheses for how leaf measurements and environmental factors correlate with greendown and decreasing NIR reflectance across sites. At the landscape scale, we used linear regression to test the effects of maximum greenness, elevation, slope, aspect, solar irradiance and canopy rugosity on greendown. Secondly, we used leaf chemical traits and reflectance observations to test the effect of nitrogen availability and intrinsic water use efficiency on leaf-level greendown, and landscape-level greendown measured from Landsat. The study was conducted using Quercus alba canopies across 21 sites of an eastern deciduous forest in North America between June and August 2014. Our linear model explained greendown variance with an R2=0.47 with maximum greenness as the greatest model effect. Subsequent models excluding one model effect revealed elevation and aspect were the two topographic factors that explained the greatest amount of greendown variance. Regression results also demonstrated important interactions between all three variables, with the greatest interaction showing that aspect had greater influence on greendown at sites with steeper slopes. Leaf-level reflectance was correlated with foliar δ13C (proxy for intrinsic water use efficiency), but foliar δ13C did not translate into correlations with landscape-level variation in greendown from Landsat. Therefore, we conclude that Landsat greendown is primarily indicative of landscape position, with a small effect of canopy structure, and no measureable effect of leaf reflectance. With this understanding of Landsat greendown we can better explain the effects of landscape factors on vegetation reflectance and perhaps on phenology, which would be very useful for studying phenology in the context of global climate changeItem COMPETITIVE RESPONSE OF INVASIVE PLANT SPECIES TO NEIGHBOR PRESENCE, IDENTITY, AND PHENOLOGY ACROSS TWO GROWING SEASONS(2013) Barry, Kevin; Dudash, Michele; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Exotic plant species invade many native communities, yet some communities are less susceptible than others. Community properties that determine resistance to or influence on invasive species performance are less studied. The target-neighbor experimental design, originally used for studies of root and shoot competition (Chapter 1), is now commonly used to determine effects of communities of species on a target plant of interest. However, intensity of competition varies between species both within and across seasons, therefore interactions between species are not static. Thus I compared the competitive response of two widespread but relatively little studied invasive species, early flowering Hesperis matronalis and later flowering Nepeta cataria. Both invasives were introduced into native species neighbor communities composed of either early, late, or a mixture of early and late growth and flowering phenologies and measured over the course of two years (Chapter 2). Additionally, invasive species introduction time into native communities was manipulated by either coestablishing the invasive with the neighbors, or introducing the invasive into established neighbor communities (Chapter 3). I predicted that target invasives would experience the most intense competition (1) when sharing the same growth and flowering phenology as their surrounding native community, due to temporal niche overlap (2) when introduced into an established native community versus when coestablished with native neighbors, and also that (3) the overall effect of neighbor presence and neighbor identity would vary with the age of the competitors. Finally, I utilized field soil probes and greenhouse plants labeled with 15N isotopes to determine the relationship between phenology and nitrogen uptake to provide a mechanistic basis for temporal niche overlap (Chapter 4). The competitive response of both invasive species' performance was dependent on plant trait measured, community age, and native neighbor phenology treatment. I found evidence for a negative effect of temporal niche overlap, but resource pre-emption by the early phenology neighbors was more prevalent than stronger competition due to a shared phenology. Despite this, field nitrogen levels were still correlated with species phenology. This body of work supports the need for more research on the factors associated with native communities' ability to resist invasion.Item 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.