Biology Theses and Dissertations
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Item 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.Item 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.Item 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.Item Interactions between an estuarine submersed plant bed and its physical and biogeochemical environment: Seasonal and spatial variation(2009) Gruber, Renee Kirstin; Kemp, William M; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Annual cycles of growth and morphology were analyzed in a bed of the canopy-forming submersed aquatic vegetation (SAV) species, Stuckenia pectinata, in relation to seasonal water quality conditions in a Chesapeake Bay tributary. A rapid accumulation of aboveground plant material occurred during the spring period of high water clarity, which aided plants in circumventing light limitation during the summer period of low water clarity. During summer, this SAV bed strongly attenuated wave energy, which contributed to growth-promoting feedback effects that improved light and nutrient availability for plants. Modification of hydrodynamic conditions also resulted in several negative feedback effects on SAV growth. Feedbacks were regulated by plant stand size and density and seasonal changes in plant canopy architecture. The findings of this study illustrate the significant impacts SAV beds can have on their local environment, improving conditions and resulting in plant growth that could not otherwise occur in this degraded system.Item Organic nitrogen and carbon transformations in a stream network of Chesapeake Bay watershed(2009) Delaney, Katie M.; Kaushal, Sujay S; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Increased export of anthropogenically-derived nitrogen in streams has contributed to increased water quality problems. I investigated in-stream transformations of nitrogen and carbon at the benthic habitat and reach network scale. Both indicated large transformations of dissolved organic nitrogen (DON) and dissolved organic carbon (DOC) along the Gwynns Falls urban stream network. In-stream transformation of DON and DOC declined from headwaters to outflow, with a mean 23% removal of DOC and 57% removal of DON. Transformation rates ranged from in-stream internal loading of 28 g/m2/day to in-stream removal of 740 g/m2/day for DOC (mean: uptake 64 g/m2/day) and in-stream internal loading of 4.8 g/m2/day to in-stream removal of 74 g/m2/day for DON (mean: uptake 3.5 g/m2/day). Urban stream networks may act as both "transporters" and "transformers" of nitrogen and knowledge regarding in-stream N transformations is critical in predicting the sources and removal of nitrogen en route to adjacent tidal waters.Item Predation by eastern mudminnows (Umbra pygmaea) on macroinvertebrates of temporary wetlands(2009) Lombardi, Susan Elizabeth; Lamp, William O.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Fish play a substantial role in aquatic food webs, yet the effect of feeding activities of small stream fish that enter seasonally-flooded temporary wetlands during periods of hydrologic connectivity is not well understood. In this study, eastern mudminnows (Umbra pygmaea) were introduced to a fishless wetland in Caroline County, Maryland, and the aquatic macroinvertebrate community did not significantly change within two weeks. Gut contents of mudminnows collected from the wetland and a stream consisted primarily of dipteran larvae; ostracods were also a common food source for wetland mudminnows. Common prey not found in gut contents but present in the wetland were tested as food, and all taxa were consumed in a no-choice predation experiment. Mudminnows have the potential to directly affect multiple trophic levels and subsequent ecosystem functioning through predatory interactions with sustained hydrologic connectivity between fish sources and temporary wetlands.Item An RNA:DNA-based index of growth in juvenile Atlantic menhaden (Brevoortia tyrannus): laboratory calibration and field assessment(2009) Edwards, Jason Lee; Miller, Thomas J; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Atlantic menhaden (Brevoortia tyrannus) is an ecologically and economically important species in the mid-Atlantic coastal ecosystem. Its population dynamics are influenced by growth and survival during juvenile occupancy in estuarine nursery habitats. Therefore, quantifying production of potential nursery areas is important to understanding population processes and defining essential fish habitat for this species. Based on laboratory growth experiments, an RNA:DNA-based growth model was developed for young-of-the-year menhaden. The temporal response of RNA:DNA to changes in feeding condition was also quantified in the laboratory. Results of these investigations indicate RNA:DNA as a reliable tool for estimating recent growth and condition in relation to habitat residency. RNA:DNA-based estimates of growth were combined with site-specific abundance estimates to evaluate the spatiotemporal variability in production of potential menhaden nursery habitats. Site-specific production estimates exhibited high spatiotemporal variability suggesting menhaden utilize a mosaic of habitats to promote production, rather than specific sites consistently generating high levels of production.Item COSTS AND BENEFITS OF COOPERATIVE INFANT CARE IN WILD GOLDEN LION TAMARINS (LEONTOPITHECUS ROSALIA)(2009) Siani, Jennifer Marie; Dietz, James M.; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In cooperative breeding species, nonbreeding individuals typically delay dispersal, forego reproduction and provide care to infants that are not their own. All caregivers must therefore balance infant demands against their own self-interests. In this dissertation I investigate the costs and benefits of cooperative infant care in wild golden lion tamarins (Leontopithecus rosalia) . In chapter 1, I examine what factors influence the distribution of infant care to clarify why helpers contribute care to infants. I find that reproductive status strongly influences infant caretaking patterns, with parents contributing significantly more infant carrying and food provisioning than helpers. Parental dominance in caretaking and the lack of variation in infant carrying or food transfers with caregiver age, sex or condition suggests that genetic relatedness dictates these caretaking decisions, with infant behavior also influencing food provisioning. In chapter 2, I investigate the effects of gestation and infant care on activity budgets and body mass to determine if infant care results in detectable short-term costs to caretakers. Tamarins are hypothesized to require assistance from nonreproductive helpers in raising offspring due to ecological (e.g. predation risk, foraging) and energetic costs of gestation and care of infants, usually twins. During gestation, reproductive females do not make behavioral changes that suggest an energy conservation strategy; however, all caregivers make behavioral changes while carrying infants to increase predator awareness and decrease energetic expenditure and are able to maintain a stable body mass throughout infant care. Cooperative infant carrying may allow individuals to balance energetic demands and mitigate predation risk, thus supporting the hypothesis that energetic costs have driven the evolution of cooperative caretaking. In chapter 3, I present the results of an acoustic playback experiment to determine the frequency and intensity of caregiver responses to infant begging vocalizations. Caregiver responses were influenced by reproductive status, sex, condition, experience, group size and activity level, but not familiarity or genetic relatedness. The variation in caregiver responses to infant vocalizations suggests that these responses are flexible and dynamic, shifting with changes in group composition and context and with individual reproductive status and physical condition.Item USE OF MOLECULAR TECHNIQUES TO ADDRESS THE EVOLUTION OF DISPLAY TRAITS IN THE PTILONORHYNCHIDAE AND OTHER PASSERIFORM SPECIES(2009) Zwiers, Paul; Borgia, Gerald; Fleischer, Robert; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Tests of hypotheses addressing the evolution of complex traits have greatly benefited from advances in the field of molecular genetics. Current molecular techniques allow for the identification of genetic variability, useful in estimating genetic relatedness and potentially explaining phenotypic variation. Here I use molecular data to address the evolution of complex traits within the Ptilonorhynchidae and other Passeriformes. My estimation of a bowerbird molecular phylogeny suggests two highly unlikely scenarios of complex trait evolution (i.e. polygyny, bower construction, decoration use, etc.); either polygyny and complex display traits evolved in parallel, or monogamy evolved from non-resource based polygyny, a transition for which no unambiguous examples could be found, and complex traits evolved once and were lost. Molecular evidence also supports the existence of four Sericulus species, dating the radiation to coincide with the upheaval of the central New Guinea mountain range, and suggests plumage coloration may be a labile trait within this group and therefore a poor indicator of species relatedness. Use of ultraviolet (UV) signals in birds is hypothesized to associate with the ability to see UV wavelengths, a trait with a well-documented genetic basis (replacements at key amino acid positions in the short-wavelength-sensitive 1 (SWS1) opsin pigment influence pigment sensitivity and potentially color discrimination). UV signal use may alternatively evolve to match the local light environment. Results from bowerbirds suggest extreme differences in UV reflectance are due to light availability and not differences in UV vision because amino acid sequences in the bowerbirds were nearly identical. Expanding upon this study, I compared SWS1 opsin gene sequences from 134 passeriform species and plumage UV reflectance measurements from 91 of these species. Results from the molecular data are unprecedented; replacements at five amino acid positions are predicted to have occurred nearly simultaneously, suggesting a constraint on UV vision evolution. Additionally, species reflect most intensely in wavelengths to which they are predicted to be sensitive. These results suggest a constraint on UV vision may also constrain the evolution of UV signals in the Passeriformes. These studies highlight the usefulness of molecular data when testing hypothesis of species and trait evolution.Item CRYPTIC DIVERSITY, ECOLOGICAL DIFFERENTIATION AND POPULATION GENETICS OF AN ESTUARINE COPEPOD, ACARTIA TONSA DANA 1849 (COPEPODA: CALANOIDA)(2009) Chen, Gang; Hare, Matthew P; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Surprising genetic diversity has been discovered in marine holoplankton, organisms that "drift" in water currents throughout their life cycle. This discovery challenges our assumptions and suggests that holoplankton species may have limited dispersal and/or have adapted to small-scale oceanographic features. In this study, I investigated population genetics of Acartia tonsa, a holoplanktonic estuarine copepod containing deeply-diverged mitochondrial lineages, on the United States Atlantic coast. The study goals include: 1) assessing its cryptic species/genetic diversity; 2) inferring evolutionary and geographic origins of its cryptic lineages; 3) testing environmental associations of cryptic lineages; 4) inferring evolutionary and ecological processes/mechanisms underlying population diversification of A. tonsa. Phylogenetic analyses of DNA sequences from two gene loci, mitochondrial cytochrome c oxidase subunit I (mtCOI) and nuclear ribosomal internal transcribed spacer (nITS), resolved five morphologically cryptic, genetically diverged lineages that were reproductively isolated species based on genealogical concordance principle. Three co-distributed, deeply-diverged mtCOI lineages (X, S, F) showed significant population differentiation within lineages and contrasting phylogeographic patterns among lineages. Population structures and isolation by distance patterns detected for all lineages suggested that dispersal of Acartia lineages was more or less limited to adjacent estuaries; geographic isolation was a key mechanism underlying population diversification of A. tonsa. The highly diversified, relatively recent lineage F demonstrated a southern center of origin in Florida with northward stepwise diversification. Its distinct localized population structure and strong association with low-salinity environments suggested that environmental stressors (such as salinity) could act as physiological barriers to gene flow, facilitating diversification of Acartia populations. Co-existing Acartia lineages were parapatrically distributed along the estuarine gradient across systems on the US Atlantic coast. Genetic, morphological and ecological evidence indicated niche partitioning and ecological differentiation of A. tonsa within estuaries. Multiple factors may have contributed to the observed parapatric distribution and niche partitioning, including selection by salinity, biological competition, and/or local adaptation. These findings in one of the best known estuarine copepods reinforce the general conclusion that marine biodiversity is substantially underestimated, not only in terms of species numbers, but also with respect to niche partitioning and the potential importance of ecological divergence in marine holoplankton.