When Ants Get Together to Make a Decision

Image collected from : Ants in Australia 

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(ISNS) — When ants are confronted with information overload and face too many decisions — about where to live, for instance — they revert to the wisdom of the crowd.

Despite having a brain smaller than the point of a pin, one ant species uses an elaborate system of sending out scouts to look for new homes. The scouts report back, and then the whole colony votes, according to researchers at Arizona State University.

The ants use chemistry and crowdsourcing, wrote associate professor of biology Stephen C. Pratt and graduate student Takao Sasaki at Arizona State University, in the current issue of Current Biology.

“They have tiny brains, but nonetheless, they are able to do quite a bit with them,” Pratt said. Honey bees also have small brains but each brain has about a million neurons, which collectively have “quite a lot of processing power.” Bees use a tail-wagging dance to communicate.

The ants involved in the ASU study, Temnothorax rugatulus are red, about one-tenth of an inch long, and live in crevices between rocks in forests in the western U.S. and parts of Europe.

The colonies themselves are not very big, usually a few hundred workers, Pratt said, and if an animal knocks a colony over, the roof falls in, or if they need more space,  the ants have to move.

But the ants live in areas in which the potential number of possible nest sites is overwhelming. One ant can’t cope with making the decision. No one is in charge in an ant nest.

“They distribute the task among colony members,” said Sasaki.

That’s where the crowdsourcing comes in.

According to Pratt and Sasaki, the ants send scouts to check out some potential home sites. The scouts look at such things as the size of the entrance and how big the cavity is. If the ant likes what she sees, she returns to the colony.

She sends out a pheromone message, “Follow me,” and another ant will join her in what is called tandem running. She takes her colleague out to view the potential site.

If the second ant likes what she sees, she goes back and repeats the process, bringing back another ant. If she doesn’t like it, she merely returns to the colony. If enough ants like a site, the colony reaches a quorum, essentially choosing the new home.

The scouts pick up their nest mates and carry them to their new homes, usually taking the nest queen along with them.

Sasaki built an experiment in which one ant had to make the decision from two potential sites and then from eight. Half the potential sites were unsuitable in both experiments. He was forcing the ants in the laboratory to do what ants in the wild would not, send one ant to make the decision for the colony, Pratt said.

Individual ants, confronted with two choices, had no problems picking the most suitable site. When faced with choosing among eight, however, an ant often selected the wrong place.

The two researchers tested a whole colony with the same choices, letting them send out more than one scout. The colonies, acting as a crowd, did equally well in both experiments, picking suitable sites 90 percent of the time.

“It’s a shared decision,” Pratt said.

Part of the advantage of the colony system, Sasaki and Pratt hypothesized, is that each scout visited only a few potential sites, minimizing the information it must process, while an individual ant, assigned to do it alone, had to visit them all and was the victim of cognitive overload.

Evolution has produced the system that best increases the possibility of colony survival.

Honey bees have a similar system, said computer scientist James Marshall, from Sheffield University in the U.K. He models social insect behavior.

What we are seeing, he said, is something like how the human body functions: millions of cells organized into one super-organism. In the case of the bees and ants, all the insects in the hive or nest form one individual organism.

“Here, it is very much of a group benefit,” Marshall said. “Like super organisms, the interests of individuals are the same as the interests of the group.”

“Cognitive overload is a growing issue for human decision making, as unprecedented access to data poses new challenges to individual processing abilities,” Pratt and Sasaki wrote in their journal article. “Human groups also solve difficult problems better when each group member has only limited access to information.”

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Joel Shurkin is a freelance writer based in Baltimore. He is the author of nine books on science and the history of science, and has taught science journalism at Stanford University, UC Santa Cruz and the University of Alaska Fairbanks

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Groups have a larger cognitive capacity than individuals

Copyright © 2012 Elsevier Ltd All rights reserved.
Current Biology, Volume 22, Issue 19, R827-R829, 9 October 2012

doi:10.1016/j.cub.2012.07.058

Takao Sasaki and Stephen C. Pratt

School of Life Sciences, Arizona State University, Tempe, AZ 85287-4501, US

Summary

Increasing the number of options can paradoxically lead to worse decisions, a phenomenon known as cognitive overload . This happens when an individual decision-maker attempts to digest information exceeding its processing capacity. Highly integrated groups, such as social insect colonies, make consensus decisions that combine the efforts of many members, suggesting that these groups can overcome individual limitations. Here we report that an ant colony choosing a new nest site is less vulnerable to cognitive overload than an isolated ant making this decision on her own. We traced this improvement to differences in individual behavior. In whole colonies, each ant assesses only a small subset of available sites, and the colony combines their efforts to thoroughly explore all options. An isolated ant, on the other hand, must personally assess a larger number of sites to approach the same level of option coverage. By sharing the burden of assessment, the colony avoids overtaxing the abilities of its members.

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• Groups have a larger cognitive capacity than individuals

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New research shows ants share decision-making to lessen ‘information overload’

Posted: September 24, 2012

Scientists at Arizona State University have discovered that ants utilize a strategy to handle “information overload.” Temnothorax rugatulusants, commonly found living in rock crevices in the Southwest, place the burden of making complicated decisions on the backs of the entire colony, rather than on an individual ant.

In a study published online in the scientific journal Current Biology, Stephen Pratt, an associate professor in ASU’s School of Life Sciences in the College of Liberal Arts and Sciences, and Takao Sasaki, a graduate student in Pratt’s lab, suggest that the key to preventing cognitive overload is found in collective decision-making, rather than in multi-tasking.

“I think the reason people are interested in this is because as humans, we can become overloaded with information – and that can possibly be detrimental both to our health and to how effectively we make decisions,” Pratt said. “There’s a sense that as a society, we are being more and more overwhelmed by information.”

Previous research has shown that ant colonies have the ability to compare the quality of two potential nest sites – even if no single ant visits both sites. Pratt and Sasaki hypothesized that a colony could choose a high-quality nest from many more options more effectively than individual ants, because each member of the colony assesses only a small part, or portion, of available sites, and then shares the information with the entire colony.

“People usually think of ants as sort of stupid, that they can’t really compare options, or that they don’t have good cognition,” said Sasaki. “But actually, individual ants can compare options, and that’s why they, too, experience cognitive overload – a well-documented phenomenon in human beings.”

The pair designed experiments with artificial nest sites to evaluate the ants’ decision-making abilities. Both colonies and individual ants were given two levels of tasks. Ants had to choose between two nests, or they had to choose among eight nests. In both experiments, half the nests were unsuitable. Nests are frequently chosen based on entrance and cavity size, as well as darkness and other features.

Researchers discovered that individual ants made much worse decisions when faced with eight options rather than two, meaning that they experienced cognitive overload. Colonies, on the other hand, did equally well with either two or eight options, showing that they could handle the harder problem as a collective.

The study shows what Pratt believes to be the answer to two questions: What do you get out of being a collective intelligence? And secondly, why and how is a group smarter than an individual?

“Living in a group is costly in many ways, so ants must get some benefit from doing it,” said Pratt. “By sharing the burden of decision-making, colonies avoid the mistakes that a solitary animal makes when taking on too much information. What’s great about these ants is that we can see exactly how they do this, by making sure that no ant has to process more information than it is able to.”

Pratt added that this is one problem ants can solve, but that there are other problems ants face that we might be able to learn from.

“What we really want is a more complete understanding as to how this society works as a kind of distributed brain,” Pratt said. He believes their research may provide insight into how to handle information excess in society and will have applications in collective robotics.

This study was supported by grants from the National Science Foundation (1012029) and the Arizona State University Graduate Research Support Program.

Editorial contributor: Gabrielle Malo

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When Ants Get Together to Make a Decision | Inside Science.
New research shows ants share decision-making to lessen ‘information overload’

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Joel N. Shurkin (2012).
When Ants Get Together to Make a Decision

Inside Science / Arizona State University

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