The regulation of foraging activity in harvester ant colonies

Ant colonies operate without central control and resemble large distributed systems. An ant's behavior depends on its recent experience of brief interactions with other ants. In the course of a brief antennal contact, one ant can assess the task of the other using odor cues. A long-term study of the behavior and ecology of harvester ants in the Arizona desert shows how colonies regulate foraging to balance the tradeoff imposed by spending water, while foraging in the desert sun, to obtain water, which is metabolized from seeds. The goal is not to send out more ants than are justified by the current food supply. The ants collect seeds that are widely scattered, each retrieved by a single ant without the use of pheromone trails. The duration of a foraging trip depends mostly on how long the forager had to search to find a seed. A forager leaves the nest on its next trip in response to the rate at which it meets foragers returning to the nest with food. Thus foraging activity is adjusted to food availability without any information about the location of food. I will discuss a model of the algorithm colonies use to regulate foraging, the ecological and evolutionary consequences of variation among colonies, and analogies to other distributed networks. 

Speaker: Deborah M. Gordon