In ancient Greece, the city-states that waited until their own harvest was in before attacking and destroying a rival community's crops often experienced better long-term success. It turns out that ant colonies that show similar selectivity when gathering food yield a similar result. The latest findings from Stanford biology Professor Deborah M. Gordon's long-term study of harvester ants reveal that the colonies that restrain their foraging except in prime conditions also experience improved rates of reproductive success. Importantly, the study provides the first evidence of natural selection shaping collective behavior, said Gordon, who is also a senior fellow at the Stanford Woods Institute for the Environment.
A long-held belief in biology has posited that the amount of food an animal acquires can serve as a proxy for its reproductive success. The hummingbirds that drink the most nectar, for example, stand the best chance of surviving to reproduce. But the math isn't always so straightforward. The harvester ants that Gordon studies in the desert in southeast Arizona, for instance, have to spend water to obtain water: an ant loses water while foraging, and obtains water from the fats in the seeds it eats. The ants use simple positive feedback interactions to regulate foraging activity. Foragers wait near the opening of the nest, and bump antennae with ants returning with food. The faster outgoing foragers meet ants returning with seeds, the more ants go out to forage. (Last year, Gordon, Katie Dektar, an undergraduate, and Balaji Prabhakar, a professor of computer science and of electrical engineering at Stanford, showed that the ants' “Anternet” algorithm follows the same rules as the protocols that regulate data traffic congestion in the Internet).