The Road from Individual to Group Position to Emergence in Whirligig Swarms

William Romey (March 15, 2011)

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Emergent patterns of flocks and swarms are at once beautiful and mysterious. We ask ourselves: "How and why do individuals coordinate these complicated maneuvers?" More specifically: how does self organization at lower levels influence emergent properties at higher levels? I will present the results of some of my studies addressing these questions using whirligig beetles and computer models to understand the three-part transition from (1) individual behavior to (2) group position to (3) the emergent behavior of swarms. Whirligig beetles make an ideal organism for studying general grouping phenomenon, such as those found in birds and fish, because they are composed of unrelated individuals, unlike bees and ants where altruism and kin-selection complicate the interpretation of emergent properties.

Working from the bottom up, we have used computer models and ethograms to examine how differences in (1) individuals influence the lower-level movement rules of the beetles. For example, sex, hunger, and age may influence an animal's preferred distance from others, and the speed with which they swim. These rules then influence the (2) group position which they occupy. For example, depending on predators and water speed, certain classes of whirligigs reliably end up at the edge or front of groups. We have modeled and carried out experiments which show that these positions are consistent with the hypothesis of self-organization: simple movement rules can explain the observed within-group segregation. Also, we present evolutionary optimization models that support the hypothesis that these group positions are individually adaptive. Finally, the group as a whole exhibits measurable behaviors (3) that seem to be an emergent property of levels one and two. These emergent properties include: group speed, turning, stopping, and mass predator escape. In conclusion we will discuss if the behaviors at all three of these levels are evolutionarily adaptive, or whether some might be neutral byproducts of an adaptive response at a different level.