Last night's lecture was delivered by Princeton's Iain Couzin, whose research concerns animal group dynamics. He started off with a basic overview of the movement of swarming or schooling animals, noting that individuals in a group tend to maintain an optimal standard distance from each other. The metric distance model shows the zone of orientation, which is this optimal distance. Modifications in the size of the zone of orientation lead to changes in the configuration of a group, from a "swarm" configuration, to a "torus" form to a "polarized" grouping. The group dynamics tend to be fluid, as the group reacts to external stimuli (such as forming "vacuoles" around predators).
When moving in groups, individuals possessing information (such as good areas for foraging) can influence the behavior of the group as a whole, although a majority of "decision" makers can influence group behavior, even if they do not possess accurate information (at this point, a wag who shall remain nameless likened such a hypothetical group to the Teabaggers- the bastard). In a case in which two equal-sized groups with conflicting "information" (e.g. two equal-sized groups of lab animals which have been trained to seek food in two separate areas) are placed in a larger group, the group as a whole will tend to move in the "average" direction between the directions favored by the two "informed" groups. This PDF file succinctly summarizes this portion of the talk.
The topic then shifted to the behavior of swarming locusts in Africa. Dr Couzin traveled to Mauritania to study swarming locusts. The swarming behavior is a defense against cannibalism- it's move or be eaten by those behind oneself. Locusts with severed abdominal nerves (who can't feel the crunchings and munchings of their peers), or locusts having had their rear-vision obstructed through the application of paint to their eyes, have less of a tendency to swarm than their jumpy, freaked-out kin, so they have a greater tendency to be eaten. In the arid, marginal habitats in which swarming locusts tend to live, one's peers tend to be the most readily available food source.
All told, another great lecture by yet another entertaining, engaging speaker.