Biology Theses and Dissertations

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    BIRD COMMUNITY RESPONSE TO CONSERVATION RESERVE PROGRAM HABITAT IN MARYLAND
    (2010) Blank, Peter Joshua; Dively, Galen P.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The populations of many bird species in the United States that use early-successional habitats have been substantially declining over the last 40 years. The main reason for these declines is habitat loss. Land enrolled in the U.S. Department of Agriculture's Conservation Reserve Program (CRP) often represents the only uncultivated herbaceous areas on farmland in the mid-Atlantic and therefore may be important habitat for early-successional bird species. CRP filter strips are strips of herbaceous vegetation that are planted along agricultural field margins and are usually planted with native warm-season grasses or introduced cool-season grasses. We studied the breeding and wintering bird use of CRP filter strips adjacent to wooded edges in Maryland from 2004-2007. We conducted bird and vegetation surveys in filter strips and measured landscape attributes around CRP plantings. We used 5 bird community metrics (total bird density, species richness, scrub-shrub bird density, grassland bird density, and total avian conservation value), species-specific densities and abundances, nest densities, and nest survival estimates to assess the habitat value of filter strips for birds. Bird community metrics were greater in filter strips than in field margins without filter strips, but did not differ between cool-season and warm-season grass filter strips. Most breeding bird community metrics were negatively related to the percent cover of orchardgrass (Dactylis glomerata). Several grassland birds were more common in wide filter strips (>60 m) compared to narrower filter strips (<30 m). The density of early-successional bird species was greater in filter strips with higher plant species richness and shorter and less dense grasses. Wintering bird use was significantly less in filter strips mowed in the fall than in unmowed filter strips. The abundance of northern bobwhite (Colinus virginianus), an important game bird and species of conservation concern, was positively associated with the percent cover of CRP land in the surrounding landscape. These results suggest that the CRP has created additional habitat for many early-successional bird species, but changes in the planning and management of CRP plantings may improve their habitat value for breeding and wintering birds.
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    Investigating the role of the Mid-Atlantic inner continental shelf as a marine finfish nursery: a comparative approach
    (2010) Woodland, Ryan Jordan; Secor, David H; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The paradigm of estuarine-dependence in marine fishes has been challenged by evidence of facultative recruitment by juveniles to both estuarine and inner continental shelf (ICS) nursery habitats. This ecological flexibility suggests that the potential nursery area for marine fishes may be more expansive than previously considered. Two lines of investigation were undertaken to evaluate the overarching hypothesis that ICS habitats serve a nursery function for finfish that also use estuarine nurseries: 1) a direct comparison of seasonal, annual and compositional assemblage structure between an ICS habitat of the Middle Atlantic Bight (Delmarva Peninsula) and an adjacent estuary (lower Chesapeake Bay); and 2) an investigation of trophic structuring within an ICS demersal finfish assemblage with an emphasis on ontogenetic niche. In comparisons between nursery types, there was a strong seasonal similarity in assemblage structure between the estuary and ICS despite significant differences in abundance estimates at the species level. Juvenile trophic niche of two indicator species, bluefish and bay anchovy, was wider and more diverse in the estuary yet physiological condition was similar or higher in the ICS. In focused studies on the ICS food web, diet overlap was common among consumers, yet stable isotope evidence indicated prey resources were partitioned along vertical (trophic position) and horizontal (pelagic-benthic pathway) trophic axes. Benthic and pelagic food webs were tightly coupled in most juvenile phase finfish; yet, this relationship showed signs of decoupling in older age classes, suggesting an increased reliance on benthic trophic pathways with age and size. Several prey species that link pelagic and benthic food webs were shown to be important in the diets of demersal finfish, particularly mysid shrimp. Comparative assemblage and food web studies demonstrated that the ICS functions as summer nursery habitat for a wide variety of temperate marine finfish that also use proximal estuarine nurseries. The contribution of ICS nurseries to annual juvenile production represents a critical, but unknown component of population demographics for many marine species and must be considered to conserve essential fish habitats and account for recruitment variability in fisheries stock assessments.
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    Stable nitrogen isotopes (&delta15N) in the eastern oyster (Crassostrea virginica) as an indicator of nitrogen source
    (2010) Fertig, Benjamin Meir; Dennison, William C; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This dissertation demonstrates that stable nitrogen isotope signatures (δ15N) in oysters (Crassostrea virginica) can identify anthropogenic nitrogen sources (a cause of degraded water quality) at multiple spatial scales in Chesapeake Bay and Maryland's Coastal Bays. Fieldwork, monitoring and land use data, spatial analyses, and modeling techniques were employed. Due to minimal tissue &delta15N variations between individuals as replicates (standard error < 0.5 /), a sample size of five individuals optimally balanced error with effort. Transplantation verified convergence of oyster &delta15N after changes in nitrogen source while modeling quantified temporal integration (four months for muscle, two to three months for gill and mantle) and measurements over two years demonstrated seasonal &delta15N increases in seston (summer) and oysters (winter). At the small scale (10s of km2), oyster tissues in Monie Bay's creeks (varying by watershed land use) were dominated by anthropogenic nitrogen transported to Monie Bay from Wicomico River whose watershed inputs were predominantly manures (6.8 x 104 to 2.4 x 106 kg N yr-1), not sewage (2.0 x 105 kg N yr-1) or septic (1.1 x 105 kg N yr-1). This has large implications for Delmarva Peninsula: home to 4,630 poultry feeding houses (generating 3.9 x 106 to 1.3 x 108 kg N yr-1) and 1.2 x 106 people (combined sewage and septic generating 3.7 x 106 kg N yr-1), thus a poultry:human nitrogen generation ratio of 1:1 to 91:1. At the medium spatial scale (100s of km2), water quality in Maryland's Coastal Bays was susceptible to runoff. Macroalgae &delta15N (Gracilaria sp.) responded rapidly (4 days) over 100s of km2, while oyster &delta15N responded slowly (2 months) over 10s of km2. Broadly, in Chesapeake Bay (large scale, 10,000s of km2), oyster &delta15N was correlated to land use, stream and tributary water quality, and it reflected tributary wastewater plumes. The overall oyster &delta15N gradient (16.0 / in Eastern Bay, 8.3 / in Lynnhaven River) decreased with flushing time, with increased salinity, and with increased shell height. Denitrification remains potentially confounding as it elevates nitrate &delta15N signals, potentially before oyster assimilation (via plankton). Nevertheless, oyster &delta15N is a powerful tool for indicating nitrogen sources across spatial and temporal scales.
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    ECOLOGY AND DEMOGRAPHY OF GOLDEN-HEADED LION TAMARINS (Leontopithecus chrysomelas) IN CABRUCA AGROFOREST, BAHIA STATE, BRAZIL.
    (2010) Oliveira, Leonardo de Carvalho; Dietz, James M; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Understanding how species use the matrix of habitat that surrounds forest fragments can contribute to conservation strategies in fragmented landscapes. In this dissertation, I evaluate the effects of habitat structure and resource availability on group characteristics, use of space, and predation risk for the endangered golden-headed-lion tamarins in shaded cocoa plantations locally known as cabruca agroforest. In the first chapter I present a list of tree species that provide key foods and sleeping sites used by lion tamarins. Families Myrtaceae and Sapotaceae are the most commonly used by lion tamarins for both food and sleeping sites. Fifty-five tree species were ranked as extremely valuable for the tamarins. Cabruca management that retains the species listed in this study may improve the long-term survival of lion tamarins. In the second chapter, I compare ecological and demographic data of lion tamarins in cabruca and other vegetation types. In contrast with my prediction that food resources would be scarce in cabruca, the exotic and invasive jackfruit (Artocarpus heterophyllus) was an abundant food resource for tamarins in cabruca while bromeliads were the favorite substrate for animal prey foraging. Group size and composition were similar in all vegetation types. Males in cabruca were heavier than those in primary forest. Density of lion tamarins in cabruca was the highest and home range size the smallest reported for the species. This is the first study to show that lion tamarins can live and reproduce exclusively in cabruca and has important implications for conservation of the species. In my third chapter, I test two hypotheses explaining the association between lion tamarins and Wied's marmoset (Callithrix kuhlii): foraging benefits and predation avoidance. I found no evidence to support the hypothesis that interspecific associations provide foraging benefits for lion tamarins. However, several findings support the predation avoidance hypothesis: associations occurred in areas where predation risk was higher, and during the part of the day in which predation risk was highest, and following birth events when the tamarins were more susceptible to predation. Despite the importance of cabruca to lion tamarins, they are more exposed to predation in this habitat.
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    GRAZING AS A MANAGEMENT TOOL FOR CONTROLLING PHRAGMITES AUSTRALIS AND RESTORING NATIVE PLANT BIODIVERSITY IN WETLANDS
    (2010) Brundage, Jennifer Emilienne; Baldwin, Andrew H; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This study examined the feasibility of grazing as a sustainable and low-impact means of controlling Phragmites. In addition, this study examined whether grazing of Phragmites by large herbivores (goats) in a wetland affects soil and soil water nutrient pools, and thus how grazing might affect nutrient export from the wetland. An isolated, created wetland at USDA's Beltsville Agricultural Research Center (BARC) in Beltsville, MD was divided into four grazed and four ungrazed plots. Two rounds of grazing significantly reduced Phragmites height, stem count, and biomass and increased some measures of plant diversity. Grazing significantly elevated soil water total nitrogen and total phosphorus levels and reduced soil water-soluble phosphorus levels. The nutrient pool analysis indicates that grazing reduced the fertility of the system. The results of this study will inform the development of an alternative, sustainable approach to controlling Phragmites that integrates the local agricultural community while benefiting the local ecology.
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    Interregional differences in stream ecosystem responses to urbanization: causes and consequences
    (2010) Utz, Ryan Michael; Hilderbrand, Robert H; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Stream ecosystems are profoundly degraded by watershed urbanization. Hydrologic, geomorphic, chemical and thermal adjustment following urban development contributes to substantial biodiversity loss in impacted streams. However, the extent of degradation along an urban gradient may not be uniform among regions. The hydrogeologic and climatic setting in which a stream is located may influence the severity of abiotic and biotic impact induced by urban development. I explored and compared differences in stream ecosystem responses to urbanization between the Coastal Plain and Piedmont physiographic regions of the eastern United States. Taxon-specific responses of fishes and macroinvertebrates as well as the coherence of benthic invertebrate communities along gradients of landscape stressors were quantified. Hydrologic, chemical and thermal impact induced by watershed urbanization was compared between the two physiographic provinces using existent large datasets collected by various governmental entities. I also compared the severity geomorphic and sediment regime alteration in urban streams between regions using direct measurements of channel morphometry and in situ natural experiments within selected watersheds. Biotic sensitivity to urbanization was consistently found to be heightened in Piedmont streams relative to those in the Coastal Plain. Such trends were consistently observed for fish and macroinvertebrate taxa as well as for invertebrate community coherence. The most tolerant macroinvertebrate communities were associated with low channel slopes, effective soil permeability and high levels of wetland cover. Rural Coastal Plain streams exhibited fewer flood events that were longer in duration; however, flood hydrology was more impacted by urbanization in Coastal Plain streams relative to those of the Piedmont. Conversely, thermal impact induced by urbanization was greater in Piedmont streams. Experimental observations concluded that benthic sediment size structure, deposition and transport were more impacted by urban development in Piedmont streams relative to those of the Coastal Plain. My findings highlight interregional heterogeneity in stream ecosystem responses to landscape change, suggesting that effective watershed management decisions may need to consider the physiographic setting in order to improve efficacy. Furthermore, results suggest that watersheds characteristic of hydrogeomorphic attributes that effectively transfer water to channels during precipitation events may be acutely vulnerable to urban development.
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    A comparative analysis of sperm storage in six brachyuran superfamilies: mating behavior, ecological variation and phylogenetic patterns
    (2010) Rodgers, Paula Jane; Reaka, Marjorie L; Hines, Anson H; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    While life history traits are shaped by allometric, phylogenetic, environmental and behavioral factors, few comparative studies of brachyuran life history patterns have considered sperm storage traits as important components of reproductive strategies. To understand the evolutionary forces selecting for sperm storage and their interactions with other life history traits, I (1) used controlled laboratory experiments and field mating observations to examine variation in male sperm transfer patterns, (2) sampled variation in female reproductive output and sperm storage for two species across a latitudinal gradient, (3) conducted a survey of life history traits across a broad range of brachyuran taxa, and (4) used phylogenetic analyses to identify patterns in the evolution of life history traits in brachyurans. From mating experiments and observations on five species, I found that males transfer more sperm with longer than shorter copulation durations and that variation in copulation duration was shaped by differences in the species' ecologies. Latitudinal surveys of two species with contrasting mating systems identified seasonal and geographical variation in female reproductive output. While the variation in most reproductive traits could best be explained at smaller spatial scales, a sperm storing species, Callinectes sapidus became sperm limited at low latitudes. From a comparative survey of male and female life history traits across 61 species of brachyurans, I found that allometry, phylogeny and mating strategies explained much of the variation in life history traits. Using rigorous phylogenetic techniques, male life history traits showed more plasticity across the phylogeny than female traits suggesting male traits may be influenced more by behavioral and environmental factors. After correcting for phylogenetic signals, species with larger male sperm stores had larger amounts of sperm stored by the female. In summary this dissertation illustrates the importance of partitioning variation in mating behavior, phylogeny, environmental factors and allometry when examining the evolution of life history traits in brachyurans.
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    Nitrogen saturation in streams and forests of the Maryland Piedmont
    (2009) Craig, Laura Shawn; Palmer, Margaret A; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Human activities have dramatically increased nitrogen (N) inputs to the landscape. Consequently, delivery of N to coastal waters, largely as nitrate (NO3-N), has increased, resulting in widespread eutrophication and harmful hypoxic conditions. The ability to mitigate the downstream effects of elevated N inputs requires a clear understanding of the transport and transformation of N in stream ecosystems. Here, I examine N processing in urban and forested watersheds of the Maryland Piedmont. I provide extensive evidence that three high-N streams draining urban and forested watersheds of the Maryland Piedmont are unable to remove NO3-N as a result of both N saturation and phosphorus limitation. My findings illustrate that when elevated NO3-N concentrations occur in the absence of other stressors that stimulate autotrophic activity (e.g. reduced canopy cover, increased nutrients) uptake cannot compensate for increased N loads. A review of the literature indicates that systems that are similarly unable to remove NO3-N vary widely in terms of land use and background N concentrations, highlighting the limitations of our understanding of N saturation in stream ecosystems. I also provide the first documentation of N saturation in both the aquatic and terrestrial components of an un-manipulated forested watershed. Detailed examination of N dynamics within the forested watershed reveals that the forest is severely N-saturated despite receiving atmospheric N inputs that are small relative to other parts of the Northeast and Mid-Atlantic. Because groundwater delivers a disproportionate fraction of the N load to the channel, in-stream N concentrations are elevated when deep groundwater flowpaths dominate, and the watershed is a source of N during dry periods, I hypothesize that hydrogeologic factors that control groundwater susceptibility to NO3-N contamination and promote delivery of NO3-N via subsurface flowpaths may exacerbate N-saturation response. My results suggest that we cannot rely on in-stream processing to reduce N loads even in minimally impacted watersheds. As a result, it is critical that management efforts reduce N loading to streams and take advantage of opportunities for increasing N removal in impaired systems only after other options have been exhausted.
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    MATRIX EFFECTS ON INDIVIDUAL AND COMMUNITY-LEVEL RESPONSES OF BIRDS TO FOREST FRAGMENTATION IN JAMAICA
    (2009) KENNEDY, CHRISTINA MARIE; Neel, Maile C; Fagan, William F; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Land cover between habitat patches ("matrix") can impact species persistence in fragmented landscapes by altering resource availability, edge effects, or inter-patch movement. This thesis examines how the matrix affects the Neotropical bird community in central Jamaica in landscapes where forest is embedded in three human-dominated matrix types (agriculture, peri-urban development, and bauxite mining) and one natural "matrix" (continuous forest). First, I examine whether richness, community composition, and abundances of resident birds differ in ~100 forest patches within the four matrix types, and relate species responses to traits influencing dispersal, resource acquisition, and/or population growth. Agricultural landscapes were found to retain avian diversity and community assemblages most similar to intact forest relative to peri-urban and bauxite landscapes. Traits related to resource acquisition best predicted species responses, indicating that resource limitation driven by the matrix may be a primary factor driving bird responses to fragmentation. Next, I determine the relative influence of patch area, isolation, vegetation structure, and matrix type on the occupancy dynamics of resident insectivorous birds. Within-patch vegetation and matrix type were the most important determinants of colonization and extinction, but the effects of patch area, isolation, and vegetation on occupancy dynamics were matrix- and species-dependent. Across the community, the matrix influenced extinction probabilities more than colonization, indicating that extinction processes likely drive population dynamics. Finally, I examine the relative permeability of peri-urban, bauxite, and forested landscapes on the movement of the migrant American Redstart (Setophaga ruticilla) and the resident Jamaican Tody (Todus todus) by experimentally translocating > 140 birds 0.6-4 km from their territories across landscape treatments. Redstarts returned with greater success and faster speed than Todies. Return success was not impacted by landscape treatment, but both species returned more rapidly in forest relative to bauxite matrix, with return times intermediate in a peri-urban matrix. These findings indicate that bird mobility in fragmented landscapes is mediated by the landscape matrix. This research is among few empirical studies to discern the impacts of different matrix types on species patterns and processes. These results inform theory on fragmentation as well as bird conservation in an understudied system.
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    CRITICAL PATCH SIZES AND THE SPATIAL STRUCTURE OF SALT MARSH COMMUNITIES
    (2009) Martinson, Holly Marie; Fagan, William F; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The size, connectivity, and quality of habitat patches can have multifaceted impacts on species and communities. In this dissertation, I combined a multi-year field survey, manipulative field experiments, and a literature review to investigate how spatial structure influences species and their trophic interactions in fragmented habitats. For all empirical work, I used as a study system the arthropod assemblage found on patches of the salt marsh grass Spartina patens. In Chapter 1, I conducted seven surveys of habitat patches over three years to examine the effects of patch size, connectivity, and local environmental conditions on a guild of specialist sap-feeding herbivorous insects and their natural enemies. I found striking differences among species in the effects of both patch size and connectivity, which led to differences in species' relative abundances and trophic structure among these patches. In Chapter 2, I manipulated host plant quality and predator density to experimentally examine mechanisms that might structure this arthropod community. I found that positive responses of herbivores to experimentally-elevated patch quality were limited by dispersal constraints and that predation by abundant generalist spiders may constrain the spatial distribution of certain species. Investigating systems beyond the marsh, I conducted a literature review and analysis in Chapter 3 wherein I examined whether the spatial structure of habitats generally influences trophic interactions. From the literature, I identified 171 studies of trophic interactions in fragmented habitats and found that the influence of fragmentation and related variables on the occurrence or strength of trophic interactions was largely predictable based on the habitat affinity of interacting species. With this dataset, I also identified key gaps in the fragmentation literature, including a heavy bias towards the study of two-species interactions. Therefore, in Chapter 4 I took advantage of my data from the salt marsh to identify how, in addition to the two-species interactions of parasitism and egg predation, more complex food web interactions might depend on variation in the size of habitat patches. Overall, my findings show that variation in patch size can have varied, but predictable, effects on patch occupancy, population density, and interactions between species in fragmented habitats.