| Mixotrophy is the ability for an organism to combine autotrophy and heterotrophy. These types of organisms are found in a variety of aquatic, estuarine and oceanic environments; however, very little attention has focused on the effects of mixotroph behavior on planktonic ecosystems. The purpose of this dissertation is to examine how complex mixotroph behaviors can affect both population- and ecosystem-level processes. This is accomplished both empirically, using simple laboratory experiments, and theoretically, through the development of ecosystem models.; Laboratory experiments using a mixotrophic dinoflagellate, Pfiesteria piscicida, were conducted to examine how mixotrophy influences the expression and rates of life stage transformations. Cultures of Pfiesteria were exposed to a variety of initial prey concentrations and light intensities and the presence of life stages were monitored through time. In addition, a numerical model was fit to the laboratory data in order to ‘back-out’ growth parameters such as grazing rates, gross growth and assimilation efficiencies, chloroplast retention times, and encystment rates. The results of the laboratory experiments and numerical model, as well as their ecological implications, are discussed in detail.; A theoretical planktonic ecosystem model was also developed to examine how mixotrophy, in general, affects population- and ecosystem-level complexity, stability, growth and development, and the invasion success of invading populations. The theoretical ecosystem model contained nine components, ranging from dissolved nutrients and detritus to mixotrophs and zooplankton. The mixotroph component was morphed to represent one of five distinct types of mixotrophs, based on conceptual and numerical models previously published, as well as one of two controls: a pure autotroph and a pure heterotroph. The model was arranged such that a large set of simulations were run, each with a unique combination of maximum uptake and grazing rates. The ecosystem descriptor used to measure complexity, stability, growth and development were applied to the equilibrium results of each of these simulations. The results, conclusions and suggestions for further studies are discussed. |
