This dissertation consists of a series of mathematical models for age-structured populations living in a chemostat, a laboratory apparatus that provides a controlled, resource-limited environment for microorganisms. Chemostat models are of considerable interest to theoretical ecologists because they can provide predictions with broad ecological ramifications that are testable in a laboratory. The models in this thesis demonstrate how age structure in a population interacts with resource and density dependence, predator-prey dynamics, and periodic environmental forcing. Age structure can cause persistent cycling in all the models, even for a single-species model with no periodic forcing. These age-structured cycles interact with predator-prey cycles to shift the location of Hopf bifurcations in parameter space, and they interact with periodic forcing to cause very complicated dynamics. All models provide specific parametric predictions for the onset of different qualitative behaviors that could be tested for real laboratory populations.
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