The Most Successful Ant Colonies Forage For Food When Conditions Are Prime, Study Shows

A decades-long study of harvester ants has offered a view into the collective behavior of ant colonies and gives unprecedented examples of the natural selection that occurs within the colonies.

It turns out that the harvester ants make decisions about when they will gather food, restricting their foraging habits unless conditions are optimal. Colonies that observed using such restraint were found to have greater reproductive success, according to a study by Deborah M. Gordon, a professor of biology at Stanford University.

A long-held belief in biology suggests that the amount of food an animal requires can serve as a proxy for its reproductive success. Hummingbirds that drink the most nectar, for example, stand the best chance for surviving to reproduce.

But Gordon found that the harvester ants don't necessarily thrive under the same principles. Gordon uses the example of harvester ants in the desert climates of Arizona. Ants there must expend precious water in order to get more of it; they expend the water foraging, then acquire more from the eating fats in the leaves the ants foraged.

It is more important for the ants to not waste water than to forage for every last piece of food, Gordan learned. But not all colonies behave the same way. Some colonies are likely to forage less when conditions are dry. Those same, more successful colonies are likely to forage steadily when condition are good.

Gordon found that not only do the colonies that hunker down on the bad days live just as long as those that go all out, they also have more offspring colonies.

"Natural selection is not favoring the behavior that sends out the most ants to get the most food, but instead regulating foraging to hold back when conditions are bad," Gordon said. "This is natural selection shaping a collective behavior exhibited by the entire colony."

The work is published in the May 16 issue of the journal Nature.