Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 92 for “"trophic level"”.
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Trophic Level Changes and Alewife Predation on Conesus Lake
… has gone through a series of changes within its trophic levels. Walleye have been declining in numbers since the early 1970's. The introduction of an obligate planktivore, the alewife, in the late 1970's resulted in a rapidly expanding planktivore population and poorer water quality. Attempts at …
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Development of a three-trophic level toxicity test utilizing an alga (Chlorella vulgaris), rotifer (Brachinous calyciflorus), and fish (Pimephales promelas)
… The system developed is a linear three-trophic level food chain consisting of an alga (Ch/ore/la vulgaris), rotifer (Brachionus calyciflorus), and fish (Pimephales promelas). The chemostat design used for the lower two trophic levels was crucial in being able to supply the top trophic …
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Bioaccumulation of persistent organic pollutants and trace metals in Scottish marine food webs and their relationship with trophic level and fatty acid signatures.
… be more difficult to sample, with generic trophic level values obtained from literature and databases adding additional uncertainty to assessments. Currently, assessment criteria for organic and inorganic contaminants either do not account for secondary poisoning as a route of exposure, or …
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Naturalization of Salt Marsh Restoration Sites in the Elizabeth River, Virginia, Assessed by Feeding Activity and Trophic Level of Mummichogs (<i>Fundulus Heteroclitus</i>)
… marshes had not reached the same functional level as the reference marshes.</p>
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Evaluation, assessment, and determination of risk to high trophic level piscivores in the Mid-Atlantic: A spatial, biological, and comparative case study of mercury in Virginia bald eagle populations
This research is focused on explaining the concentrations of mercury found in juvenile bald eagles (Halieattus leucocephallus) as a function of the physical and anthropogenic landscape. Due to it's location in the food chain this species is susceptible to a wide range of contaminants (xenobiotics), …
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Reproductive biology, morphology and diet of Raja straeleni (spotted skate) in South Africa
… Annelida (1.9%), and Nemertea (1.9%). The trophic level of R. straeleni was 3.98 ±0.05 SE. The trophic level was previously calculated as 3.74 (n = 421) (Ebert and Bazzarro 2007). The difference in findings is a result of a higher incidence of squid in the diet of skates examined in this …
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Investigation of possible dietary differences between the inhabitants of the Robberg/Plettenberg Bay and Matjes River Rock Shelter in the later Stone Age : an isotopic approach
… Fur seals), representing the lower and higher trophic level marine foods important in prehistoric diets along the coast.
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Movement Ecology and Trophic Dynamics in the northern Gulf of Mexico: Implications for Fisheries Management
… and recreational fisheries ranging from low-trophic-level species, such as penaeid shrimps and forage fishes, to high-trophic-level predators (e.g. Yellowfin Tuna). This thesis contributes to the region’s ecological knowledge, with the primary aim of enhancing management efforts and providing …
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Stable carbon isotopes in deep time : the diets of fossil fauna and hominids
… between collagen and apatite changes with trophic level.
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Interannual variability in Indian Ocean surface waters and tuna-environment relationships : filling the gaps with a coupled bio-physical ocean model
… basin-scale controls on productivity and higher trophic levels. A lack of in situ data, especially for mid and upper trophic-level organisms, has commonly limited to small spatiotemporal scales, investigations into environmental control of biological systems. These data gaps are increasingly …
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Mercury Concentrations in Fish from the Guadalupe River, Texas: Relationships with Body Length and Trophic Position
… the concentration of Hg in muscle tissue from 41 trophically diverse species (n = 1,772) in relation to body length and trophic position at five sites on the Guadalupe River in South Central Texas using a direct mercury analyzer and stable isotope analysis (δ13C, δ15N). The majority of fishes …
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Ecological evaluation of coral reef resources at Kahaluʻu Bay, Hawaiʻi
… and numerical abundance (total fish and by trophic level). The impacts of abiotic factors are based on species thresholds. Individual biotic requirements of all fish and by trophic level are influenced by space or shelter availability and food. Differences in abiotic and biotic preferences …
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Predicting ecological impacts of climate change and species introductions on a temperate chalk stream in Southern Britain - a dynamic food web model approach.
… the loss of a keystone species causes a catastrophic change in community composition. Therefore, the identification of keystone species could help to target conservation efforts more effciently. A dynamical food web model, representative for a chalk stream (the River Frome, Dorset) was …
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Of fish, pigs and cesspits : a comparative study of stable carbon and nitrogen isotope analyses on animal bone and soil samples from five medieval sites in Belguim
… yielded the lowest δ¹⁵N values, indicating a low trophic level diet with little influence from fish. The highest trophic level diet was recorded in the cesspit at Aalst. At Walraversijde, the low representation of marine foods was very surprising, apparently contradicting the abundance of fish …
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Effects of competition, disturbance and productivity on the dynamics of inducible trophic polymorphism in tetrahymena vorax
Inducible trophic polymorphism enables organisms to alter their trophic level when facing environmental changes, and therefore can ameliorate the intensity of competition. The freshwater ciliated protist Tetrahymena vorax was found to have three distinct phenotypic morphs with two trophic levels. …
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Permanent Coexistence for Omnivory Models
… the consumption of resources from more than one trophic level. In this work, we investigate three omnivory models of increasing complexity. We use the notion of permanent coexistence, or permanence, to study the long-term survival of three interacting species governed by a mixture of competition …
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Are PCBS in phytoplankton and zooplankton at equilibrium with the water in which they live?
… result in harmful concentrations within higher trophic level organisms such as fish and humans. It is important to consider how the concentrations of PCBs in phytoplankton and zooplankton affect higher trophic organisms. It was hypothesized that polychlorinated biphenyl (PCB) concentrations …
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Effects of selected pollutants on grazer utilization of Aufwuchs
The trophic level impact of structural changes in Aufwuchs communities resulting from low levels of stress can be assessed through analyses of the nutritive value of the microfloral community in conjunction with measurements of grazer consumption rates and assimilation efficiencies. Artificial …
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FACTORS AFFECTING MERCURY BIOMAGNIFICATION IN RIVERINE FOOD WEBS IN THE ROCKY MOUNTAINS: CLARK FORK RIVER BASIN, MONTANA, U.S.A.
… in mercury concentration in three riverine trophic levels (aquatic invertebrates, fish, and osprey). I find that the mercury concentrations of low trophically positioned species, like aquatic invertebrates, are extremely dependent on mercury source concentrations (p=0.0143). While, species …
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FACTORS AFFECTING MERCURY BIOMAGNIFICATION IN RIVERINE FOOD WEBS IN THE ROCKY MOUNTAINS: CLARK FORK RIVER BASIN, MONTANA, U.S.A.
… in mercury concentration in three riverine trophic levels (aquatic invertebrates, fish, and osprey). I find that the mercury concentrations of low trophically positioned species, like aquatic invertebrates, are extremely dependent on mercury source concentrations (p=0.0143). While, species …
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