Thesis (Ph. D.)--University of California, San Diego, 2000. / Vita. Includes bibliographical references.

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Body size influences virtually all aspects of the autecology of material flow by organisms. Thus, size classes may be considered as alternatives to grouping by trophic level, function or taxonomy to describe the structure and function of communities. The general intent of this thesis is to assess the role of body size in the dynamics of radiophosphorus in the freshwater plankton. To calculate a priori estimates of the fluxes of phosphorus through size classes of plankton, the rates of assimilation and excretion of laboratory cultures of algae and cladocerans were measured, and regressed on body mass (W). In both groups, assimilation increased as W('0.75). The turnover of body phosphorus was described as a two-compartment system. The turnover rates of the small (2-5% of body P) fast turnover pool, the large (95-98%) slow turnover pool, and that of the body phosphorus fell proportionately to W('- 1/4) in algae and W('- 1/2) in zooplankton. Field tests of allometric models of radiophosphorus flow were conducted by following the redistribution of radioactivity among 11 size fractions of enclosed epilimnetic assemblages over 5 to 6 days. Concentration of the tracer in the biomass declined with size soon after addition and gradually shifted to a uniform distribution within 3 days. A model that makes no a priori assumptions as to the trophic structure of the system, i.e. all size classes are at the same trophic level, predicted these dynamics better than one that assumes trophic position to increase with size. Further analyses indicated that explicit treatment of the physiological allometry and size distribution of broad functional groups of plankton are needed to improve the descriptive power of the model further.

This study determines the effects of variations in suspended biomass, organic carbon, and pH on the time course of 2,2$ sp prime$,4,4$ sp prime$,5,5$ sp prime$-hexachlorobiphenyl uptake by laboratory cultures of Selenastrum capricornutum. Variations in pH had no effect, but uptake was enhanced by higher levels of biomass and depressed by higher levels of organic carbon. The coefficients for these measured effects on hexachlorobiphenyl were combined with existing relations based on molecular connectivity (X) or capacity ratio (K$ sp prime$) to yield semi-empirical equations to predict the instantaneous rate of uptake and bioconcentration factor (BCF) of organic contaminants as: eqalign{& rm Log rate = {-}3.30 + 0.32 X + 1.1 Log biomass {-}0.42 Log Abs cr& rm Log BCF = 4.11 + 0.86 Log K sp prime {-}0.87 Log biomass {-}0.22 Log Abs cr} / The utility of these equations was assessed by comparing time courses of hexachlorobiphenyl uptake predicted from them with time courses observed in water from eleven Quebec lakes.

The hypothesis that aquatic biomass is uniformly distributed over logarithmic size classes was evaluated with samples from epilimnetic plankton communities. Although the hypothesis is true for oligotrophic lakes, biomass increases between successive size classes in mesotrophic and eutrophic lakes. The abundance of organisms in logarithmic size intervals is strongly negatively correlated with size. The relationship between organism size and physiological performance in mixed communities was examined by testing the hypothesis that limnoplankton respiration rates are predictable functions of mean body size. The equation governing this relationship was found to be similar to those obtained with laboratory cultures. The total epilimnetic phosphorus concentration is correlated with both biovolume and respiration rate. Many limnological relationships, including those established in this thesis, are based on linear regressions between log-transformed variables. The rules for the correct use of backtransformed predictions are elucidated. A theorem is proven, which sets limits to the relationship between the coefficients of determination on the original and transformed scales. Simulated data and empirical results are used to illustrate the applications and limitations of the theoretical results.

Typescript (photocopy) / Bibliography: leaves 163-177. / Microfiche. / xi, 177 leaves, bound ill., maps 29 cm

Typescript. / Thesis (Ph. D.)--University of Hawaii, 1965. / Bibliography: leaves 186-193. / xix, 193 l graphs, maps, tables, mounted photos