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Calow (1983) realized that differences between parasites and their free-living relatives can be explained by the differences in nutrient richness. I propose a model that is based on Calow's idea which identifies the relative position of different trophic strategies (e.g. predation, grazing, parasitism and others) based on (1) the differences by which consumers arrive at their intrinsic rate of growth, and (2) the ecological impact they inflict on their hosts. I hypothesize that trophic interactions can be clarified if a parameter is included that takes into account the host's/prey's fate in the interaction. Moreover, this model suggests specific trophic evolutionary pathways (TEPs) between each strategy, and suggests that some pathways are more likely than others. In particular, parasitoidism is believed to be a highly derived strategy, and the TEPs presented in the model suggest parasitoidism could have arisen from either a predator-like or a typical-parasitic ancestor. Though the trophic categories determined by the model seem intuitive, this approach does provide, apparently for the first time, an objective, mathematically and ecologically useful basis for classifying animal trophic relationships. / Graduation date: 1998

Graduation date: 1995

Thesis (Ph. D.)--Lehigh University, 2002. / Includes vita. Includes bibliographical references (leaves 121-132).

 This study primarily aimed to evaluate the usefulness of fatty acids (FAs) in revealing trophic relationships in Hong Kong wetlands, through a combination of field studies and laboratory experiments. A field-based study in Mai Po mangroves involved FA profiling of basal food sources (i.e., leaf litter from three mangrove species, diatoms and macroalgae, and sediments) and consumers (particularly crabs). FA composition of all mangroves was similar, and lacked some polyunsaturated FAs present in diatoms and macroalgae. Uca and Sesarma crabs, with different feeding mechanisms, had divergent FA profiles: Uca arcuata FAs reflected a diet of macroalgae and diatoms, while FAs of Sesarma spp. were typical of mangrove leaves. Temporal changes in consumer FA profiles between 2001 and 2007 appeared attributable to increased sedimentation at Mai Po and shifts in organic content of the substratum. A second field-based study was conducted at Luk Keng marsh where a salinity gradient (0 to 30?) allowed investigation of the effects of salinity changes in FA profiles and stable isotope (carbon and nitrogen) signatures of the consumers and their foods. Basal food sources were leaf litter, including a fungal biomarker of decomposition (ergosterol), fine particulate organic matter (FPOM) and periphyton. Both FPOM and periphyton (but not leaf litter) contained 20:4 and 20:5 FAs, but their concentrations were affected by salinity. FA 20:4 occurred at higher levels in samples from fresh water, whilst FA 20:5 exhibited the opposite pattern and was more abundant under saline conditions, and thus the ratio of FA 20:4 to FA 20:5 decreased with increasing salinity. Combined application of FA biomarkers and isotopic signatures were able to elucidate trophic relationships between consumers and their food at Luk Keng confirming that FA 20:4 as a useful biomarker in the freshwater portion and FA 20:5 in the more saline area. FA 20:4 was particularly associated with predatory freshwater insects that had high δ15N values, but was scarce in primary consumers (snails, detritivorous beetles) with low δ15N values. Two laboratory experiments were undertaken to investigate: 1) the effect of diet on FA profiles in the apple snail, Pomacea canaliculata, and 2) interacting effects of diet and salinity on FA profiles of the Indian medaka fish, Oryzias melastigma. The results of the apple snail study showed that dietary-mediated changes in FA profiles were only reflected in the snail tissues after at least three months, and FA profiles of digestive tissues and neutral lipids were first to respond to the dietary change. The results of the medaka study demonstrated that the ratio of FA 20:4 to FA 20:5 was affected by both diet and salinity, reflecting a similar finding in the Luk Keng field study, although diet had a stronger effect on this ratio. The results of both field studies supported the use of FA profiles as food web tracers in wetlands and were complemented by laboratory results that yielded insights which will allow refinement of FA biomarker applications in food-web studies. / published_or_final_version / Biological Sciences / Doctoral / Doctor of Philosophy

Deeper understanding of the factors controlling stable isotopic signatures of aquatic organisms of all trophic levels is required if we are to properly use them in food web studies and as environmental indicators. The present field study conducted in the Ste. Marguerite River system, Quebec, compared periphyton signatures found in eight reaches (sections of a river/tributary) each composed of a series of sites with different flow regimes. Similar to patterns found in the laboratory, periphyton delta13C significantly decreased with increasing water velocity. In addition, periphyton biomass positively affected periphyton delta13C. Isotopic fractionation in favour of 12C by the periphyton communities likely leads to build-up of the heavier isotope in the boundary layer of algae. This study allows a better understanding of aquatic plant delta13C fluctuations. It also suggests how much variability in aquatic consumer delta13 C can be explained by water velocity in lotic systems.

This thesis examines a number of natural and anthropogenic disturbances within marine macrophyte habitats of the Caribbean. Understanding the effects of disturbance and the patterns associated with such dynamics is fundamental to ecological studies. Dynamics of interest included: interactions between populations; interactions between life history strategies; successional regimes; and alterations of community structure including loss of trophic heterogeneity and the possibility of "alternate" states. First I explored natural physical disturbance and succession. The dominance of macroalgae in the mid-shore, between areas of seagrass, challenged "classic" succession in such communities. I therefore proposed a model that included chronic "stress" by wave energy that could lead to a reversal in the climax state. Next, I investigated the importance of other grazers (i.e. trophic heterogeneity) in mediating the strength of trophic cascades (e.g. overgrazing). The enclosure experiments used suggested that different life history strategies respond differently to experimental conditions and that interference competition between specialist (conch) and generalist (urchins) grazers results in urchins switching to alternate resources and displaying lower condition. This dynamic may indirectly "buffer" the community against population expansions of urchins and overgrazing of diversity enhancing detritus. Under high nutrient enrichment, urchins maintained themselves, the trophic cascade and low diversity by switching to "expanded" autochthonous and "new" allochthonous resources. I continued to examine the effects of increasing nutrient enrichment, which correlated well with increasing human density, by examining eleven seagrass beds. The patterns of increasing consumer density and decreasing consumer diversity corresponded well to increasing enrichment and loss of autochthonous detritus. At high levels of enrichment, the community was dominated (> 90%) b

A dual stable isotope approach (delta13C and delta15N) was used to assess the importance of pelagic organic carbon in littoral secondary production and explore its predictability. Forty-seven sites were sampled in Lake Memphremagog (Quebec--Vermont) to characterize the isotopic position of the primary producers and filter-feeding freshwater mussels, as well as macrophyte biomass, chlorophyll-a concentration, and site exposure. The different sites spanned a wide range in the three environmental variables. For each site, littoral, terrestrial, and pelagic contributions to the diet of the mussels were calculated from mussel isotopic position, corrected for trophic enrichment. The mean contributions were: littoral---8%, terrestrial---27%, and pelagic---65%. However, the magnitude of the pelagic contribution was not related to macrophyte biomass, site exposure or chlorophyll-a concentration. The finding that the unionid mussels, a major littoral zone filter-feeder, obtain about two-thirds of their nutrition from pelagic zone particles washed into the littoral zone provides evidence for a close coupling in carbon flow of the littoral and pelagic zone. This study represents an important step towards a better understanding of carbon flow in aquatic food webs.

Thesis (M.E.S.)--The Evergreen State College, 2007. / Title from title screen (viewed 1/24/2008). "MES thesis." Includes bibliographical references (p. 79-88).

Thesis (Ph.D.)--University of Western Australia, 2006.