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.population dynamics

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Now showing 1 - 6 of 6
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    EFFECTS OF ENVIRONMENTAL VARIABLES AND CHANGES IN SEASONAL PATTERNS ON SPATIAL DISTRIBUTIONS OF JONAH CRABS (CANCER BOREALIS) AND ATLANTIC ROCK CRABS (CANCER IRRORATUS) IN GEORGES BANK AND THE MID-ATLANTIC BIGHT, USA
    (2023) Wade, Kaitlynn Jean; Wilberg, Michael J; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The economic and commercial importance of Jonah crabs (Cancer borealis) and Atlantic rock crabs (Cancer irroratus) has increased greatly in the USA. The objectives of my research were to determine spatial distributions, habitat preferences, and potential seasonal movements of both species. Data were obtained from the offshore Northeast Fishery Science Center bottom trawl surveys. Analyses included kernel density estimates, generalized additive models, empirical cumulative distribution functions, and ANOVAs. The spatial distributions of Jonah and Atlantic rock crabs changed over time during the 1970s – 2000s. Compared to Atlantic rock crabs, Jonah crabs preferred slightly warmer temperatures, deeper depths, and muddier sediments. Seasonally, Jonah crabs were found farther offshore in the winter and closer to shore in the fall and spring. Atlantic rock crabs were found closer inshore in the winter and spring and more offshore in the fall. Both species were found to have different seasonal patterns in the Mid-Atlantic Bight
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    INTEGRATING BIOTELEMETRY AND HYDROACOUSTIC DATA TO ESTIMATE THE ABUNDANCE OF THE FALL SPAWNING RUN OF ATLANTIC STURGEON IN THE MARSHYHOPE CREEK-NANTICOKE RIVER SYSTEM
    (2022) Coleman, Nicholas; Secor, Dr. David H; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Once thought to be extirpated, fall spawning runs of Atlantic sturgeon (Acipenser oxyrinchus) have been rediscovered in the Nanticoke River-Marshyhope Creek system in Maryland and are currently listed as an endangered species within the Chesapeake Distinct Population Segment. Previously tagged adults predominate survey captures, suggesting a very small population size. A key challenge is to estimate abundance for such a small population distributed between presumed spawning reaches of the connected Nanticoke River and Marshyhope Creek. This study leverages data collected from a dense telemetry receiver array and multiple side-scan sonar surveys conducted from August to October to estimate reach specific and superpopulation abundances in 2020 and 2021. I modified an approach that integrates mobile hydroacoustic data with biotelemetry, here applying for stationary telemetry receiver data. In 2020 and 2021, I estimated that 36 (95% confidence interval: 25-55) and 74 (95% confidence interval: 52-109) sturgeon used the Nanticoke River-Marshyhope Creek system, respectively. The higher estimate in 2021 coincided with higher sonar count data and low and stable river flows and temperature. Still, this large difference has no clear cause. Overall, run estimates support previous hypotheses that the Nanticoke system supports a very small population and that both the Marshyhope Creek and upper Nanticoke River serve as important areas for spawning activity. Going forward, enhanced sampling of the Upper Nanticoke River and targeted analysis assessing the relationship between phenology and environmental conditions would further develop our understanding of interannual changes in spawning run abundance.
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    Mathematical Models for Ovarian Cancer
    (2017) Botesteanu, Dana-Adriana; Levy, Doron; Applied Mathematics and Scientific Computation; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Ovarian cancer is the most fatal cancer of the female reproductive system. High-grade serous ovarian cancer (HGSOC) represent the majority of ovarian cancers and accounts for the largest proportion of deaths from the disease. From a clinical perspective, the complex, heterogeneous behaviors of this women's cancer pose questions that cannot always be answered with contemporary clinical and experimental tools. Studying the growth, progression, and dynamic response to treatment of ovarian cancers in an integrated systems biology/mathematical framework offers an innovative tool at the disposal of the oncological community to further exploit readily available clinical data and generate novel testable hypotheses. Developing novel physiologically structured mathematical models to study the heterogeneous behavior of this malignancy would help us to better understand patient therapeutic responses and devise novel combination therapies. As a first step, we developed a mathematical model for a quantitative explanation why transvaginal ultrasound-based (TVU) screening fails to improve low-volume detectability and overall survival (OS) of HGSOC. This mathematical model can accurately estimate the efficacy of screening for this cancer subtype. The model also explains the observed heterogeneity in cancer progression and duration of the pre-diagnosis stage. Our mathematical model is consistent with recent case reports and prospective TVU screening population studies, and provides support to the empirical recommendation against frequent HGSOC screening. At the cell population level, we have quantitatively investigated the role of cell heterogeneity emerging from variations in cell-cycle parameters and cell-death. Many commonly used chemotherapeutic agents in treating ovarian cancers target only dividing cancer cells. We recently demonstrated in a mathematical model, calibrated against published in vitro cell culture data, that resistance to chemotherapeutic treatment may arise from a dynamic, oscillatory balance between the dividing and non-dividing cancer cells, which is conserved through time despite high long-term drug dosages. At the single cell level, we developed a mathematical model to explain the emerging heterogeneity in individual cancer cell responses to drugs targeting the cell-cycle, which have a broad spectrum of anti-tumor activity in ovarian cancers. This emerging heterogeneity remains a poorly understood mechanism that plays a significant role in mediating drug response, and predicts the existence of an intrinsic resistance mechanism to drug therapy. The model incorporates an intrinsic form of heterogeneity via the duration of time single cells spend in mitosis. It uses published single cell in vitro experimental data for calibration. Herein, the goal is to better understand why, within a distinct cell line, cells treated with identical drugs exhibit a considerable degree of heterogeneity in response to prolonged drug exposure. The model can serve as a basis for future studies of the heterogeneity observed in vitro of more complex responses to anti-mitotic drugs of different cell lines. Studying the natural history, growth, and progression of ovarian cancers in an integrated systems biology/mathematical framework represents a complementary tool that can be used to provide valuable insights into the treatment of HGSOC. My work focuses on developing and applying quantitative, integrated mathematical modeling frameworks to pre-clinical and clinical data, in order to better understand ovarian cancer dynamics and develop new therapeutics.
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    An evaluation of the synchronization in the dynamics of blue crab (Callinectes sapidus) populations in the western Atlantic
    (2011) Colton, Amanda Rae; Miller, Thomas J; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Blue crab populations along the east coast of the United States are known to fluctuate in size annually. Previously, the degree of coherence in abundance between these populations was unknown. My research used a combination of fishery-dependent and fishery-independent data to quantify the amount of synchrony among blue crab populations and to determine the mechanisms that drive abundance fluctuations. This was done by first fitting catch-survey models to time series of survey abundance and catch to obtain absolute abundance estimates. Subsequently, I used multivariate techniques to quantify the extent and pattern of synchronization. I found that a latitudinal pattern among blue crab populations exists among all the regions except Chesapeake Bay, which appeared to be anomalous. A combination of larval mixing in the coastal ocean and a Moran effect appear to be drivers of the synchrony among blue crab populations although more investigation into these mechanisms is needed.
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    Ecological interactions of the cadmium- and zinc-hyperaccumulating plant, Thlaspi caerulescens, and their implications for phytoremediation
    (2011) Che-Castaldo, Judy P; Inouye, David W; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The success of invasive species can be attributed to a combination of abiotic factors, such as abundant resources and favorable climate, and biotic factors, such as low levels of competition and predation or herbivory, at the introduced location. While studies have demonstrated the effects of these factors on known invasive species, the degree to which these factors affect a non-native species can be used to predict its likelihood of becoming invasive. The metal-hyperaccumulating plant Thlaspi caerulescens (Brassicaceae) is potentially useful for remediating soils that are moderately contaminated with Cd and Zn, and has been experimentally introduced to contaminated sites outside of its native range for phytoremediation. To assess the ecological risks involved in introducing metal-hyperaccumulating plants for phytoremediation, including their potential invasiveness, I have performed three studies to examine the abiotic and biotic factors that could influence the establishment of T. caerulescens at three contaminated sites near the Rocky Mountain Biological Laboratory in Gothic, Colorado. In the first two studies, I test the effects of soil metal concentrations and interspecific competition on plant performance, and in the third study I examine the strength of herbivore pressure on this plant. Results from these studies show that the growth rate of T. caerulescens in field conditions is generally low, but higher where there are high concentrations of soil Zn and low concentrations of soil Cu. Interspecific competition between T. caerulescens and a native congener is weak overall, and herbivory pressure from a native Lepidopteran herbivore is also low. Therefore, abiotic conditions are more limiting to T. caerulescens than biotic interactions, and would likely prevent T. caerulescens from becoming invasive or spreading outside of contaminated soils at these sites. In the fourth chapter, I use a long-term dataset to describe the demography of Frasera speciosa (Gentianaceae), a long-lived monocarpic plant. Results show that the population is stable, and despite the low elasticity values for the reproductive stages, masting events must be observed to describe accurately the population dynamics of this species.
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    Cause, consequence, and prevalence of spatial structure of white perch (Morone americana) populations in the Chesapeake Bay
    (2008-12-11) Kerr, Lisa A.; Secor, David H.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Partial migration defines the simultaneous occurrence of migratory and resident groups within populations. Using otolith chemistry (strontium:calcium measures), I documented partial migration for an estuarine-dependent white perch (Morone americana) population in the Patuxent River estuary (Chesapeake Bay, MD). Previous research indicated that as juveniles, a portion of the population remained resident in freshwater natal habitats and another portion dispersed down-estuary into brackish water habitats. I established these behaviors are alternative life history tactics that persist over the lifetime of individuals. Through back-calculation of hatch-dates, juvenile contingents were associated with their respective larval cohorts, indicating that spatial structuring was influenced by time of spawning, and temperature and prey conditions experienced during early life history. Dispersive individuals originated primarily from earlier spawned larval cohorts, characterized by slower growth and higher mortality rates compared to later spawned cohorts, which contributed disproportionately to the resident contingent. Laboratory experiments revealed that partial migration was associated with varying energetic tactics, with dispersive contingent fish exhibiting higher consumption and faster growth rates subsequent to migration. The prevalence of contingent behavior within other white perch populations in Chesapeake Bay was explored using otolith stable isotope (δ18O) values, which had a positive relationship with salinity and together with otolith δ13C serve as a proxy for regional habitats distributed along an estuarine salinity gradient. Resident contingent fish dominated Upper Bay and Potomac River populations, whereas the dispersive contingent dominated within the Choptank, Nanticoke, James, and York Rivers. The consequences of spatial structuring to productivity (spawning stock biomass), stability (variance in spawning stock biomass), and resilience (years to rebuild the population) of white perch populations were examined using an age-structured simulation model. Increased representation of migratory fish resulted in increased population productivity and resilience, whereas presence of the resident contingent within the population contributed to stability. Increased population stability and productivity also occurred when the abundance of the two contingents varied inversely to one another over time (i.e., asynchronous dynamics). The different roles contingents play in mediating population dynamics and long-term persistence highlights the importance of managing for conservation of spatial structure within fish populations.