Dynamics of Marine Zooplankton: Social Behavior, Ecological Interactions and Physically-Induced Variability

Ariane Verdy, Ph.D., 2008
Glenn Flierl, Advisor

Marine ecosystems reflect the physical structure of their environment and of the biological processes they carry out. This leads to spatial heterogeneity and temporal variability, some of which is imposed externally, and some of which emerges from the biological processes themselves. The main focus of this thesis is on the formation of spatial patterns in the distribution of zooplankton arising from social interactions between individuals. In the Southern Ocean, krill often assemble in swarms and schools, the dynamics of which have important ecological consequences. I adopt a quantitative framework to describe the dynamics of predator and prey populations and to address the costs and benefits associated with social behavior. First, I formulate a model of resource utilization by a predator population with density-dependent reproduction. Second, I incorporate the predator-prey dynamics into a spatially-explicit model. Third, I derive a weakly nonlinear model for the spatial distribution of biomass and examine the formation of one-dimensional patterns driven by social tendencies. Fourth, I simulate the schooling behavior of zooplankton in a heterogeneous resource field. Finally, I consider two sources of temporal variability in ecosystem dynamics: transient amplification of small perturbations to stable equilibrium solutions, and climatic variability affecting the local biogeochemical environment.