Evolution and social behavior in krill


Ariane Verdy and Glenn Flierl



We simulate the formation of social aggregations in a turbulent fluid environment. The theoretic al framework is employed to investigate the ecological consequences of spatial patchiness in the density-distribution of krill, which often assemble in swarms or schools. In the first part of the paper, we describe the formation of aggregations resulting from the interplay of social forc es and population dynamics. We consider an idealized ecosystem model of zooplankton with social behavior who feed on phytoplankton; this is solved analytically for the initial growth of patche s and numerically for the steady-state distributions of predator and prey biomass. Environmental variability changes the linear instability criterion for spontaneous aggregation. The second pa rt of the paper addresses the evolution of social behavior in a population with density-dependen t mating success. The model simulates the transmission of a gene controlling social behavior; na tural selection determines whether the grouping or non-grouping type becomes dominant. It is fou nd that the behavior can evolve when mixing occurs rapidly enough for resources to remain availa ble to the clustered organisms. Turbulent advection prevents the grouping type from becoming dom inant if the shear of the flow is strong enough to disrupt the patches; otherwise the aggregated zooplankton benefit from enhanced diffusion of resources by the turbulent flow.




09/05/07: Received final version with U.S. GLOBEC Contribution Number.