Individual-based Perspectives on Grouping

Glenn Flierl, D. Grunbaum, S. Levin, D. Olson

We examine the processes by which organisms form groups and the influence of environmental variability and transport. For aquatic organisms, the latter is especially important --- will sheared or turbulent flows disrupt organism groups? To analyze such problems, we use individual--based models and study the environmental and social forces leading to grouping. The models are then embedded in turbulent flow fields to gain an understanding of the interplay between the forces acting on the individuals and the transport induced by the fluid motion. Instead of disruption of groups, we find that flows often enhance grouping by increasing the encounter rate among groups and thereby promoting merger into larger groups.

We have also transformed the individual--based models into continuum models for the density of organisms. A number of subtle difficulties arise in this process; however, we find that a direct comparison between the individual model and the continuum model is quite favorable.

These studies lay the groundwork for incorporating the effects of grouping into models of the large scale distributions of organisms as well as for examining the evolutionary consequences of group formation.