Masters Theses

Date of Award


Degree Type


Degree Name

Master of Science


Life Sciences

Major Professor

David Talmy

Committee Members

David Talmy, Suzanne Lenhart, Steven W. Wilhelm, Christopher Strickland, Stephanie N. Kivlin


Harmful algal blooms are widespread in lake ecosystems but the ecological factors underlying their formation and maintenance are poorly understood. We revisit classical ecological theories which characterize and evaluate contrasting bottom-up and top-down influences on the selection of phytoplankton groups, such as Microcystis aeruginosa. We begin with a data compilation and analysis of environmental data from Lake Erie. This data analysis of nutrient concentrations, pigment concentrations, and zooplankton biomasses helps us understand and interpret what is happening in the environment throughout the year. Thus, allowing us to build a mathematical model to test our hypothesis. Our mathematical model asses a community in which two producers compete for a resource, which is supplied at a high constant rate and a consumer which can feed on either producer. Raised nutrient input may enhance selective pressure for defensive groups when high cell densities lead to high contact rates between predators and prey. We report work which evaluates whether these idealized predictions hold in more complex models which account for non-equilibrium influences associated with variable resource supply and temperature. Overall, we hypothesize that increases in resource inflow and temperature increase contact rates between predators and prey, shifting selection pressure toward defense against predation, which may be a major reason why Microcystis aeruginosa are selected in hyper-eutrophic lakes.

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