Thesis (M.S.)--Oregon State University, 2002. / Typescript (photocopy). Includes bibliographical references (leaves 41-44). Also available via the World Wide Web.

No description available.

I investigated how competitor species respond to chemical cues released from the red tide dinoflagellate Karenia brevis. K. brevis produces a mix of unstable, relatively polar, allelopathic organic molecules that are produced and released at low concentrations. The production of these compounds also varies greatly within and among strains of K. brevis. The majority of these compounds caused sublethal reductions in competitor growth. In laboratory experiments, these compounds inhibited the growth of competitors Asterionellopsis glacialis, Skeletonema grethae, Prorocentrum minimum, and Akashiwo sanguinea, although each species was susceptible to a different sub-set of K. brevis compounds. Cell physiological state and population densities were important in dictating the susceptibility of competitors to allelopathy: phytoplankton were most susceptible to K. brevis allelopathy when in earlier growth stages (rather than later stages) and in lower cell concentrations. However, these compounds have limited negative effects on natural, mixed populations of competitors from both near and offshore environments, and competitors from inshore and offshore environments appear to respond similarly to K. brevis allelopathy. In the sensitive competitor, Thalassiosira pseudonana, allelopathic compounds ultimately caused a reshuffling of cellular nitrogen pools, altered carbon storage and impaired osmotic regulation as determined using a nuclear magnetic resonance (NMR) based metabolomics approach. By characterizing the pool of primary metabolites present in the cell after exposure to K. brevis cues, we inferred which metabolic pathways may be affected by allelopathy. For instance, concentrations of betaine and the aromatic metabolite homarine were suppressed, indicating that K. brevis allelopathy may disrupt this competitor’s ability to osmoregulate. Exposure to K. brevis cues enhanced the concentrations of glutamate and the fatty acid caprylate/caprate in T. pseudonana, suggesting that protein degradation was enhanced and that energy metabolism was altered. This contrasts with the response to K. brevis allelopathy of the diatom Asterionellopsis glacialis, which was much more resistant to chemical cues produced by K. brevis, likely through as yet unidentified detoxification pathways. Overall, my dissertation research provides insight into how species-specific, antagonistic interactions among phytoplankton competitors can affect community structure through direct or indirect mechanisms, highlights the potential role of allelopathy in the maintenance of K. brevis blooms, and uses a novel tool set (i.e., metabolomics) to determine the molecular targets of K. brevis allelopathy. It further demonstrates that planktonic communities are complex and dynamic ecological systems and that interspecific interactions between phytoplankton can have unexpected, cascading impacts in marine systems.

Two populations of Barbados Zenaida dove (Zenaida aurita) have in previous work been found to use two radically different modes of feeding competition. The St. James (StJ) population is territorial; it competes aggressively with conspecifics but scramble competes with heterospecifics. The Deep Water Harbour (DWH) population forages nonaggressively in large homospecfic flocks. Earlier studies linking these social differences with differences in individual and social learning suggest that Z. aurita is ideal for testing predictions from Brown's (1964) theory of economic defendability. Firstly, the hypothesis that resource defence will increase as the spatial clumping and temporal predictability of a resource increases was tested at 6 sites at DWH with a randomized complete block design. Secondly, spatial distribution of food was manipulated at both DWH and StJ in an attempt to alter the mode of foraging competition at DWH from scramble to interference, and to elicit group-feeding in the otherwise territorial StJ doves. As predicted, rates of aggression per intruder were highest for those sites at DWH receiving a spatially clumped and temporally predictable food source. Unlike those at DWH, doves from StJ did not modify their mode of foraging competition in response to variations in spatial distribution, but rather as a consequence of increased resource density. Interference competition appears to be the default strategy for Zenaida doves, with birds switching to scramble competition when a threshold of resource density is reached, only to revert back to aggressive defence when the spatial clumping and temporal predictability of food increases.

Laboratory experiments examined now aggressive behavior, use of space, activity and breathing frequency were affected by the number of fish competing for a concentrated, renewing, intermittent food source. Total aggression rate per fish and the proportion of long chases decreased in larger groups and increased during short periods in which food was unavailable. The proportional use of the area near the food source was maximal at intermediate group sizes suggesting that use of the feeding area was reduced by aggressive defense at low densities and by passive interference at high densities. Air-breathing frequency tended to be lower when food was available than when it was not, suggesting that gouramis reduce their use of atmospheric oxygen when it may result in loss of food to competitors. Group size affects the pattern of food competition more through economic resource defense than through passive interference.

Data taken from the literature were used to develop and evaluate models predicting fish biomass and yield, crustacean zooplankton biomass, and profundal macrobenthos biomass in lakes. Total phosphorus concentration and macrobenthos biomass/mean depth were the best univariate predictors of fish biomass and yield. Phosphorus concentration was also the best predictor of zooplankton and macrobenthos biomass. In experiments testing for inter- and intraspecific competition, conducted in situ at densities based on measured natural fish densities, growth of yellow perch (Perca flavescens) and pumpkinseed (Lepomis gibbosus) reared alone was inversely related to density. Both species primarily ate macroinvertebrates when reared alone. When reared together: perch growth was significantly depressed compared to that of perch reared alone; pumpkinseed growth was equivalent to that of pumpkinseed reared alone; and the diet of perch changed to include food of inferior quality (microcrustaceans) in the presence of the superior competitor, pumpkinseed, whose diet did not change.

This thesis examines whether juvenile feral pigeons, Columba livia, form sibling alliances when competing for access to a defensible food source. When tested as a flock at a non-depletable column feeder, with room for either one or two birds to feed, siblings associated with each other more often than expected by chance. Frequency of aggression between siblings at these feeders tended to be lower than expected on the basis of their association. Removal experiments showed that sibling presence had a positive effect on relative feeding success at the single column feeder: a juvenile who lost to another juvenile on a one-to-one basis tended, in the presence of its sibling, to lose less badly to, or even beat, that same juvenile. In contrast, presence of the winner's sibling tended not to affect the relative feeding success of competitors. These results support the hypothesis that pigeon siblings form aggressive alliances when competing for food that is defensible.

This thesis examines whether scramble competition is associated with social learning. The question is explored via a comparative study involving two species of grassfinches, Amadina fasciata, and Taenopygia guttata. These finches vary in the degree to which they employ scramble competition while foraging, but are otherwise similar behaviourally and morphologically. General problems associated with the application of the comparative method to the testing of learning specializations are discussed. Functional improvements to previously employed approaches are proposed, and then implemented in a novel methodology and statistical approach to analysing the data, the Manova approach. The results of the study suggest that there is no link between scramble competition and social learning in these two species. When the effects of confounding variables are removed from the interspecific comparison, the species do not appear to differ in their social learning abilities. The results also indirectly suggest that some forms of social learning occur through the mechanisms of general learning.

Thesis (Ph. D.)--Biology, Georgia Institute of Technology, 2008. / Committee Chair: Kubanek, Julia; Committee Member: Hay, Mark; Committee Member: Jiang, Lin; Committee Member: Pavia, Henrik; Committee Member: Snell, Terry.

Thesis (M.S.)--Montana State University, 2004. / Title from PDF title page (viewed Feb. 11, 2005). Includes bibliographical references (p. 98-109).