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Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1990. / Vita. Abstract. Includes bibliographical references (leaves 89-99). Also available via the Internet.

Thesis (M.S.)--Oregon State University, 1989. / Typescript (photocopy). Includes bibliographical references. Also available via the World Wide Web.

Thesis (M.S.)--University of Wisconsin--Madison, 1984. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (M.S.)--University of Wisconsin--Madison, 1981. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

No description available.

No description available.

No description available.

Understanding how energy flows through ecosystems reveals underlying ecological patterns that can drive processes such as growth and survival of organisms. To understand how energy is transferred through organisms, the energy content or energy density (ED) of both consumers and prey must be determined. To facilitate the ease of ED measurement across taxa, I developed a model to estimate the ED of organisms using percent ash-free dry weight (AFDW). Using data obtained from 11 studies with broad taxonomic, temporal and spatial coverage, I compared common predictors of ED using linear models. AFDW was determined to be the superior predictor of ED relative to previous metrics and was predictive for a broad range of taxonomic groups including aquatic invertebrates, aquatic vertebrates, aquatic plants and terrestrial invertebrates. This AFDW model enables measurement of ED with minimal cost and time investment, which allows ED to be more readily determined for diverse taxa. Next, I applied the AFDW method to the diet of a pelagic consumer, juvenile Chinook Salmon, to determine the effect of variable prey ED on growth. In 2017, I collected monthly zooplankton and fish samples of known importance in the diet of juvenile Chinook Salmon to look for fine-scale taxonomic, temporal and spatial differences in ED. Decapod zoeae and megalopae differed significantly from each other and showed family level variability in ED. Amphipods also showed significant species-level variability in ED. Temporal differences were observed, but did not reveal a consistent pattern among groups. Spatial variability was not significant. Using bioenergetics models, growth of juvenile Chinook Salmon was predicted to be greater when using fine-scale ED estimates. This difference was not substantial on average, but in some cases represented more than a two-fold difference in growth between coarse- and fine-scale estimates. These results suggest the need for higher resolution diet ED data when determining growth projections for juvenile Chinook Salmon. With the aid of the AFDW model presented in this thesis, the effort required to obtain these data is greatly reduced. / Graduate / 2020-03-25

Turbidity has generally been viewed as having detrimental effects on fish; yet, many turbid habitats in the world are also abundant with fish. This phenomenon is often explained as fish enjoying reduced predation pressure in turbid habitats. This represents a trade-off situation where fish should select clear or turbid habitats that provide maximum net benefits. Because turbidity reduces light penetration, both predator and prey visual ranges are reduced, rendering both less efficient foragers. For this reason, I suspected that the benefits of a turbid environment would be greatest in the presence of predators and hypothesized that when predation risk is high, prey should prefer turbid water. Laboratory experiments showed that regardless of predation risk, fathead minnows (Pimephales promelas) preferred feeding in a turbid habitat. The presence of a predator, yellow perch (Perca flavescens) or black bullhead (Ameiurus melas), caused minnows to reduce feeding. There was on interaction between water clarity and predation risk, water clarity and predation risk, thus, appeared to affect the minnows’ habitat selection independently. The predator’s effect on the prey was the same whether in turbid or clear water. Using the prey distributions established in the lab experiment, key parameters and assumptions were identified for a computer model which simulated both prey and predator responses to turbid water and their interactions. The model predicted that prey would always prefer the turbid habitat when one was available. Predators generally used both clear and turbid habitats. Only when its foraging efficiency was reduced significantly did the predator show strong avoidance of turbid water. As the number of predators increased, predators used both clear and turbid habitat more evenly. Turbid environments seem to provide important habitats for small and juvenile fish. It may benefit small fish by reducing predator efficiency or reduce prey energy expenditure. / October 2006