Biology Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/2749

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Start date: 2000End date: 2009

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    Interannual and Regional Patterns of Abundance, Growth, and Feeding Ecology of Larval Bay Anchovy (Anchoa Mitchilli) in Chesapeake Bay
    (2003) Auth, Toby D.; Houde, Edward D.; Marine Estaurine and Environmental Science Program; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
    Patterns in abundance, growth , and feeding by larval bay anchovy were examined in Chesapeake Bay from 1995-1999 to evaluate factors that contribute to variable recruitments of this abundant fish. The patterns were examined in relation to environmental factors, including hydrography and distributions of prey (zooplankton) and a probable predator (ctenophore). Larval abundances, sizes, feeding incidences, and growth rates varied annually and regionally. Averaged over five years, mean abundances in July decreased by almost two orders of magnitude from the mouth (38.l/m2) to the head (0.6/m) of the Bay, a long a declining salinity gradient. Yearly survey, bay-wide mean abundance varied nearly 10-fold; it was highest in 1998 (42. 7 /m2) and lowest in 1996 (4.6/m2). Feeding incidence was highest in 1998 (23%) and lowest in 1996 (9%), and varied regionally from 27% in the upper Bay to 13% in the mid Bay. Larvae fed predominantly during daylight. The most common prey ingested were copepod eggs and various life stages of calanoid copepods (primarily Acarlia Lonsa). Growth rates of larvae also differed annually and regionally. Mean growth rate was highest in 1998 (0.81 mm/d) and lowest in 1999 (0.68 mm/d), and varied regionally from 0.83 mm/d in the upper Bay to 0.71 mm/din the mid Bay. Zooplankton concentration was positively correlated with larval feeding incidence (r = +0.66) and growth rate (r = +0. 72). Larval feeding incidence was strongly correlated (r = +0.93) and summer larval abundance significantly correlated (r = +0.86) with fall recruitment of young-of-the-year bay anchovy.
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    Understanding Maternal Effects as a Recruitment Mechanism in Lake Michigan Yellow Perch (Perca flavescens)
    (2000) Heyer, Christopher James; Miller, Thomas J.; Biology; Marine - Estuarine - Environmental Sciences Program; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
    Changes that have occurred in the abundance and trait distribution of adult Lake Michigan yellow perch (Perca flavescens) suggest that maternal effects on larval traits may be substantially influencing the recruitment of this heavily exploited species. Maternal effects on yellow perch larvae at hatching and through 32 days post hatch (dph) were investigated in ten maternal lines to test the null hypotheses of no effect of maternal condition on offspring condition at hatching, no persistence of maternal effects under conditions of starvation and high food availability, and no difference in offspring survival under conditions of starvation and high food availability. Maternal effects were detectable at hatching and likely result in differences among females in size, age, gonadal somatic index, and egg production. Maternal effects at hatching were expressed by differences in larval total length, yolk volume, dry weight, and DNA quantity. Maternal effects persisted under conditions of starvation to 6 dph, after which point virtually all larvae had perished. Maternal effects resulted in a twofold difference in resistance to starvation among the maternal lines. Larvae that exhibited the lowest resistance to starvation were long with small yolk volumes, while those exhibiting the highest resistance to starvation were short with large yolk volumes. Under high food availability maternal effects persisted to 32 dph, and resulted in threefold differences in survival among the maternal lines. No clear mechanism was identified to account for these survival differences. The observed maternal effects in Lake Michigan yellow perch may have substantial implications on recruitment.
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    Morphology in Urbanized Streams of the Puget Sound Lowland Region
    (2004) Boyle, Pamela; Prestegaard, Karen; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The purpose of this research is to evaluate the effects of urbanization on channel morphology. Three hypotheses are tested: 1) Channel morphology measured from one cross section is not similar to reach-averaged values, 2) Channel shear stress ratios and erosivity increase with urbanization, and 3) Channel morphological complexity decreases with urbanization increases. Results indicate that single cross-section data do not adequately describe channel morphology. Shear stress and bed mobility did not increase with urbanization, perhaps due to the presence of large bed grain sizes that adjust to increases in flow. Similarly, channel complexity did not decrease with increased urbanization. These data indicate that channel changes resulting from urbanization are influenced by sediment supply as well as discharge, and that this should be taken into consideration in restoration design.
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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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    RELATIONSHIPS BETWEEN LARVAL MORPHOMETRICS AND SETTING EFFICIENCY IN THE EASTERN OYSTER, CRASSOSTREA VIRGINICA
    (2009) Vlahovich, Emily Ann; Meritt, Donald W; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    In oyster hatcheries, the decision to move larvae from rearing tanks to setting tanks is based on physical and behavioral characteristics. These criteria can suggest conflicting action and a more reliable method may result in higher spat production. I observed hatchery reared Crassostrea virginica larvae, beginning with larvae retained on a 200 µm sieve. Aliquots of larvae were measured or placed in a setting vessel, and the remaining were returned to the culture cone daily. Each day had an associated setting efficiency, loss, and set of larval morphometrics, including shell height and length and eyespot diameter. Day was most strongly correlated with setting efficiency. Eyespot diameter was moderately correlated with setting efficiency, and shell morphometrics were weakly correlated with setting efficiency. I estimated daily spat production, which peaked on day 2. These results suggest spat production may be increased by altering current hatchery methods to consider eyespot diameter or days past retention on a 200 µm sieve when deciding to place larvae in setting tanks.
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    Benthic Oxygen Production in the Choptank Estuary
    (2009) Chick, Christopher Roberts; Cornwell, Jeffrey C; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Microphytobenthos (MPB) represent an important component of primary production in many coastal estuarine systems. The aim of this study is to determine which variables in the Chesapeake Bay are positively correlated with MPB oxygen production, and based on this correlation to develop a predictive relationship for estimating benthic primary production. Furthermore, this study estimates the proportion of MPB primary production to total primary production in the Chesapeake Bay. Oxygen flux rates were measured in the dark and in the light from sediment cores taken from three sites on the Chesapeake Bay. Flux rates ranged from 6000 mol O2 m-2 h-1 in the light to -3800 mol O2 m-2 h-1 in the dark treatment. From these rates and other measurements, we developed multiple linear regressions using sediment grain type and depth to predict oxygen production seasonally. We applied these relationships to sediment grain-size and bathymetry data using ArcMap software to create a spatial dimension to our predictive relationships. Based on our derived relationship, we estimated summer average benthic daily net production to be 123 ± 962 mg O2 m-2 d-1 between 0-3 meters. For the winter, we estimated the rate to be 152 ± 413 mg O2 m-2 d-1. For spring we had a weaker relationship, but we estimated benthic production to be -257 ± 123 mg O2 m-2 d-1. Using published pelagic data, we created a proportion of benthic to pelagic primary production, and we estimate that MPB provide approximately 12% of total primary production in the mid-bay region. Shallower depths contained a higher proportion of benthic O2 productivity to pelagic O2 production with the contrast peaking during the summer months.
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    CHEMICAL INDUCTION OF SETTLEMENT IN LARVAE OF THE EASTERN OYSTER CRASSOSTREA VIRGINICA (GMELIN)
    (2009) Grant, Melissa; Meritt, Donald W.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Although numerous studies have been conducted to examine the effects of neuroactive compounds on bivalve larvae, few have identified chemicals capable of inducing settlement behavior in the eastern oyster Crassostrea virginica. In this study, I treated competent C. virginica larvae with select chemicals to identify those which are capable of inducing settlement behavior at an average salinity of 9.6 (±0.1). The compounds γ-aminobutyric acid and acetylcholine chloride, both at 10-4M, did not significantly increase the percentage of larvae exhibiting settlement behavior. As compared with the control, a significant increase in settlement behavior was induced by treatment with 3-isobutyl-1-methylxanthine, 5-hydroxytryptamine, and L-3, 4-dihydroxyphenylalanine all at 10-4M, as well as ammonia as a solution of 7.9mM NH4Cl (pH=8.0). These findings differ somewhat from the results of similar studies involving other species in the Crassostrea genus and may be of value to hatchery personnel or researchers interested in the chemical induction of settlement behavior in the eastern oyster.
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    Genetic Differentiation of Selected Eastern Box Turtle (Terrapene carolina) Populations in Fragmented Habitats, and a Comparison of Road-based Mortality Rates to Population Size
    (2009) Hagood, Susan; Adams, Lowell; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The decline of eastern box turtle populations is associated with habitat loss and fragmentation, lack of recruitment into breeding populations, removal of individuals from the wild for pets, and road mortality. Box turtle populations in many areas of the eastern United States may effectively be isolated as high traffic volumes on roads adjacent to turtle habitats prevent successful dispersal. If so, populations surrounded by heavily used roads may be less genetically diverse than those in relatively intact habitats. I investigated whether populations in three Montgomery County, Maryland parks that were surrounded by roads were genetically differentiated relative to populations in two larger habitats in Maryland's Prince George's and Anne Arundel counties. Sampling was conducted between 2005 and 2008. I used 10 microsatellite markers to compare these populations, and sampled in an additional five sites (two in Maryland, and one each in Pennsylvania, the District of Columbia, and Florida), to better assess population structure. I found little evidence of genetic differentiation among central Maryland populations regardless of the extent of isolation. I attribute these findings to the slow rate of change in turtle evolution; the observed similarities in genetic diversity may reflect past rather than present gene flow. I found moderate to great differentiation in populations separated by substantial distances. To determine whether road mortality exceeds additive mortality levels believed to be a threat to population persistence, I estimated population size in the three Montgomery County, Maryland, parks using mark-recapture techniques, and compared these estimates to the number of dead, injured, and live turtles in or very near roads observed during walking and driving surveys conducted in 2006. Road-based morality rates fell within the range estimated to be inconsistent with population growth in one of the parks. Road mortality appeared to affect females out of proportion to their abundance in the population. Suggestions for reducing box turtle mortality in areas associated with high mortality rates are included.
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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.