Local processes and global patterns: Biomathematical models of bryozoan feeding currents and density-dependent aggregations in Antarctic krill

Many ecological processes are the expressions on a global scale of interactions between functionally autonomous individual modules operating on a much smaller, local scale. The characteristics of these processes are determined, frequently in subtle and counter-intuitive ways, by the rules which are followed by the component modules. In such dual-scale systems, the relationships between higher level effect and lower level cause, and the consequent evolutionary and ecological implications, cannot be properly understood without a detailed mechanistic, quantitative model of interactions at the local level. This dissertation is a presentation of studies of two biological systems in which global patterns arise as the collective outcome of dynamical interactions between individual modules.;The first study, described in Chapter 1, is a numerical model of the hydrodynamic interactions between zooids of an encrusting bryozoan, Membranipora membranacea. The model results suggest that these interactions may underlie both the function and the organizational scheme of coordinated feeding structures (excurrent chimneys), and account for the cost of induced defensive spines. Experimental results which support these hypotheses are described in Chapter 2.;The second study in this dissertation is an analysis of the impact of schooling and swarming behaviors on biomass distributions in Antarctic krill, Euphausia superba. In the first part of this study, Chapter 3, a continuum (partial integro-differential equation) model of group swarm dynamics is derived from a stochastic model of swarming individuals. The stochastic swarming model employs individuals with a finite sensing distance and a species-specific target number of neighbors. The continuum model accurately approximates the group dynamics of the stochastic model if individual locations can be described as Poisson points. The effect of social behavior on the density distributions and power spectra of a species in a forced advection environment is examined in Chapter 4. The results suggest that social behavior in Antarctic krill may account for the unexpectedly high variance observed in krill biomass at short length scales.