UMD Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/3

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 given thesis/dissertation in DRUM.

More information is available at Theses and Dissertations at University of Maryland Libraries.

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    REFINING METAGENETIC ENVIRONMENTAL DNA TECHNIQUES FOR SENSITIVE BEE COMMUNITY MONITORING
    (2023) Avalos, Grace; Richardson, Rodney T; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Molecular taxonomic detection is now widespread across the sciences, because of advances in direct PCR, improved marker selection, and increases in sequencing throughput. Facilitated by these advances in sequencing, methodological sensitivity of sample identification has improved substantially. Metagenetic techniques to infer what species are present in a sample by sequencing unknown samples and comparing them to known references has the potential to advance our understanding of biodiversity. Metagenetic analysis of environmental DNA (eDNA) represents a novel, non-lethal method for characterizing floral-associated arthropod communities. Diverse arthropod assemblages interact with flowers, and floral surfaces have been shown to harbor arthropod DNA. We performed metagenetic sequencing on eDNA isolated from flower samples and honey bee-collected pollen samples using multiple markers and compared the frequency and taxonomic breadth of eDNA detections across these genetic markers and substrate types. Understanding which markers and substrates are most effective for eDNA characterization of floral-associated arthropod communities will guide future research and enable low-risk detection of threatened or endangered arthropods.
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    Marine Community Assembly in a Dynamic Ecotone
    (2016) Johnston, Cora Ann; Gruner, Daniel S; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Species distributions are shifting with climate change. By altering the presence and distribution of biogenic foundation species, climate change effectively modifies habitat. Where biogenic habitats meet, a patchy ecotone landscape forms. The impacts that range shifts and habitat modification have on broader ecological communities will depend in part on how communities assemble in frontier landscapes of patchy habitat. Here, as a case study, I investigate marine fauna community formation and habitat associations along a wetland ecotone in which tropical mangroves invade temperate saltmarsh. When foundation species shift ranges, resulting changes in geographic context and local conditions will affect the contributions of dispersal limitation and species sorting to assembly. By evaluating the presence of community structure – grouping of species – in larval supply and settlers in each pure landscape and into the ecotone, I determine that ecotone marine communities are shaped by habitat-based sorting but not dispersal limitation. Where inhabitant species can access the ecotone, the attributes that inform habitat use and the scale(s) at which inhabitants distinguish between habitat types within an ecotone should determine the apparency of emerging patches along the range edge, affecting the precision with which inhabitants occupy them. I monitored marine fauna within an experimental array that isolated physical structure from broader habitat patch attributes, revealing that nested scales of habitat sensitivity should result in increasing community divergence as habitat patches expand along the range edge. Finally, habitat associations at settlement may be driven by preference or survival. I determine habitat-specific recruitment patterns of Callinectes spp. (Decapoda: Portunidae) crabs in the ecotone and use lab trials to determine that associations are driven by preference for and superior survival in vegetation with branched architecture. Together, these results demonstrate that marine fauna are sensitive to changes in structural attributes and fine-scale emergence of mangrove habitat within marshes, which do not provide equivalent habitat. This work also contributes to our understanding of community formation in a transitional landscape, illuminating the influence of patchy foundation species expansion on community-structuring ecological processes.
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    Influences of the biotic and structural components of Crassostrea virginica on the oyster reef community.
    (2015) Kesler, Karen Elizabeth; Paynter, Kennedy T; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The hard, complex reef structure created by the eastern oyster, Crassostrea virginica, provides refuge and habitat that protects many organisms, allowing them to settle, survive, and spawn. In addition, oysters create copious amounts of biodeposits, which potentially serve as a basal nutrient resource for the reef ecosystem. I investigated the influence of oyster reef structure and oyster biodeposits on the reef community through a series of field experiments and mesocosm studies. Initially, the communities that colonized live oyster reefs were compared to communities that colonized empty oyster shell reefs, to evaluate the potential influence of live oysters that were actively feeding and creating biodeposits. Community assemblages on the two reef types were similar and no differences were seen with species level comparisons of abundance or biomass between the two treatments. The impact of oyster shell structure on energy transfer up the food chain from the basal resource of oyster biodeposits to the predator, Gobiosoma bosc, through the amphipod, Melita nitida was then investigated. Oyster shell structure effectively provided protection to amphipods, with reduction of predation impacts in high complexity habitats when a predator was present. Next, stable isotope signatures (d13C and d15N) of dominant reef species and basal resources, including oyster biodeposits, were measured seasonally to evaluate the major resource contributors to the reef. Overall, most carbon sources appeared to be pelagic in nature and an additional unidentified carbon source from outside of the oyster reef was incorporated into the food web. Finally, a d15N tracer study, utilizing biodeposits labeled with elevated d15N values, indicated that both Melita nitida and Neanthes succinea could incorporate Crassostrea virginica biodeposits and pass these nutrients to higher trophic levels. These studies suggested that oyster structure played a prominent role in defining the oyster reef community by providing habitat and protection for reef organisms. Mesocosm studies and isotopic analysis indicated that while some deposit feeders could consume oyster biodeposits, biodeposits were likely not a large component of their diet. Overall, these results suggest that structure was the dominant factor driving community organization on the reef, with minimal influence from oyster biodeposits.
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    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.
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    Ecological dynamics of macrolepidoptera feeding on box elder (Acer negundo L.)
    (2008-08-29) Lind, Eric; Barbosa, Pedro; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Understanding species abundances and distributions is a major goal of ecology. Although manipulative experiments can reveal mechanistic properties of interactions among a small number of species, and macroecological studies can draw fundamental insights from patterns at a large scale, inference about local communities as a whole requires a combination of these approaches. I used a suite of techniques to better understand the ecological dynamics of a group of insect herbivores, the assemblage of moth caterpillars feeding on box elder, a common riparian tree. I examined the landscape ecology of the assemblage to determine the degree of turnover at multiple scales, and how diversity of the assemblage depended on host plant context. I found apparent homogeneity of caterpillar diversity masked important differences in co-occurrence even at small scales, though the expected influence of host plant diversity was not observed. Examining the species through time, I investigated how species abundance was related to body size, intrinsic population growth rate, and diet breadth. Whereas body size did not scale significantly with abundance in this group of species, and diet breadth had a complex relationship with abundance, the population growth rate developed in association with the host plant explained the differential abundance of species on the plant quite well. Finally, I quantified elemental content of species in the group, to determine how stoichiometric constraints related to size and growth rates of caterpillars in the assemblage. I found some support for a theory connecting elemental composition to ecological interactions, though the results were species-dependent. Throughout these investigations I explicitly considered the evolutionary relatedness of co-occurring species using phylogenetic methods. By merging ecological and phylogenetic data, a more unified picture of the important mechanisms underlying species properties can be obtained. Through tests of theory at the landscape, community, and individual level, I have presented a clearer picture of the forces structuring this assemblage of caterpillars, and provided a template for investigations of community dynamics at a similar scale.