Avoiding Gridlock

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Science  03 Jan 2003:
Vol. 299, Issue 5603, pp. 19
DOI: 10.1126/science.299.5603.19b

Many ant and termite species set out from the nest in columns, to scour the neighborhood for food. Like commuters in the rush hour, these crowded columns face the problem of congestion, and in some species form distinct traffic lanes. Foraging army ants in the Panamanian tropical rain forest traverse the forest floor in huge, high-speed columns of tens of thousands of workers and often form a three-lane structure in which outward-bound ants occupy two outer columns while the homeward-bound ants occupy the center.

Couzin and Franks have developed a mathematical model of ant behavior to investigate this pattern, which takes into account factors such as the ability of individual ants to follow pheromone trails and to detect each other's presence and avoid collisions. This individual-based model shows that local interactions and individual movements, especially asymmetry in turning rate between two interacting ants, can generate the observed three-lane structure. This self-organizing system appears to minimize the potential for congestion, allowing the ants to return to the nest by nightfall with the maximum quantity of prey. The model does not require that the individual ants attempt to minimize their journey time, which may have a cost to others. By contrast, individual humans tend to behave selfishly in traffic, with a rather different outcome. — AMS

Proc. R. Soc. Lond. B 10.1098/rspb.2002.2210 (2002).

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