No description available.

No description available.

Thesis (M.S.)--University of Wisconsin--Madison, 1968. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (Ph. D.)--University of Washington, 2006. / Vita. Includes bibliographical references (p. 107-114).

Abstract Not Provided. / Thesis / Master of Science (MSc)

A model of the chemostat involving two populations of microorganisms competing for two perfectly substitutable, growth limiting nutrients is developed. To describe nutrient uptake, a general class of functions is used which allows for the effects that the consumption of one resource may have on the consumption of the other. It includes as a special case the model studied by Waltman, Hubbell and HSu [21] in which they generalize Michaelis-Menten functional response for a single resource to two perfectly substitutable resources. It also generalizes the model studied by Leon and Tumpson [12] where the consumption of each resource is unaffected by the consumption of the other. Analytical methods are used to obtain information about the qualitative behaviour of the model. Interesting similarities are found between both the local and global behaviour in this model and in the model for perfectly complementary resources. / Thesis / Master of Science (MS)

No description available.

No description available.

The availability of substrates is one of the most important environmental constraints on the diversity and functioning of microorganisms. Substrate quantity and quality as well as the metabolic features of heterotrophic microorganisms determine the efficiency, speed and type of transformation that can occur in nature. As such their interplay with the environment regulates how much carbon and energy is incorporated by bacteria and subsequently reaches higher trophic levels. In lakes the bulk substrate that is available for bacteria is composed of a complex mixture of compounds, varying in lability and distribution in the environment. This thesis addresses the coupling of organic substrates, their metabolic use and the composition and ecology of the microbial community. Controlled laboratory experiments with mixed bacterial communities in either batch cultures or chemostats were designed to shed further light on bacterial use of labile and quantitatively significant carbon compounds. I show that different amino acid substrates only exert a minor influence on bacterioplankton community composition and growth. Hence the ability to use a wide range of such abundantly produced protein monomers seems to be widespread among freshwater bacteria. In contrast, when acetate was provided as the only carbon substrate, in either pulsed or continuous amendments, this very different substrate input mode had a strong effect on bacterial community composition. Biomass yield, for example, was twice as high when acetate was given in the form of pulses rather than provided continuously. In another set of experiments, I show that the oxidation of the globally significant greenhouse gas methane is a process that can potentially take place at the water-ice interface of seasonally ice-covered lakes and was not constrained by temperature as suggested in previous studies. This work also suggests that methane oxidation in ice-covered lakes can be constrained by competition for nutrients between specialized methanotrophs and heterotrophic bacteria. Combined these studies suggest that some labile substrates cause minor selection on bacterial community structure and functioning. This probably reflects the competitive advantage of using a broad range of low molecular weight substrates. However, as in the case of methanotrophs there is specialization for a specific low molecular weight substrate such as methane. In which case, competition with other community members i.e. for nutrients can constrain methane oxidation. In both cases it might however not depend just on the availability of substrate, but also on how substrates are distributed in time and space.

Biological models of predator-prey interaction have been shown to have high sensitivity to the functional form of the predator response (see [3]). Chemo- stat models with competition have been shown to be robust under various forms of response function (see [15]). The fcus here is restricted to a simple chemostat model with predator-prey dynamics. Several functional responses of Holling Type II form are considered. The sensitivity of dynamics to our choice of functional form is demonstrated by way of bifurcation theory. These results should be a warning to modelers, since by data collection and curve- fitting alone it is impossible to determine the exact functional form of the predator response function. / Thesis / Master of Science (MSc)