Bigger groups make better choices

By Katie Duncan 16 February 2011
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Fish in groups are quicker and more accurate at making decisions than individuals.

MORE HEADS ARE BETTER than one when it comes to decision making, at least if you’re a fish, according to new research.

Scientists from the University of Sydney have found that large groups of fish are more efficient in making decisions than small groups or individuals.

“If by simply joining a group, an animal can access much better information and use this to make better decisions, it’ll be more likely to survive to reproduce,” says lead author and marine ecologist Dr Ashley Ward.

Based on previous research, Ashley expected fish in larger groups to be more accurate in choosing the path without the predator. But he didn’t anticipate the difference in speed to be so significant.

“What we didn’t necessarily expect was that the fish in larger groups would be so much faster. In fact, they spent around half as much time on the decision [making],” he says.

Testing fish decision-making

The scientists presented groups of the mosquitofish (Gabusia holbrooki), with a choice to swim down one of two forks in a Y-shaped maze. One fork contained a replica predator, while the other fork did not. The fish were rated on how quickly and accurately they chose the non-threatening path.

Using this set-up, Ashley and colleagues found that fish in larger groups of eight or more made incredibly efficient, high-quality decisions in comparison to fish in pairs or singles. The single fish tended to zig-zag around, ostensibly to gather information in an uncertain environment, Ashley says. Whereas, larger groups of fish swam in a more direct path.

“This appears to be because they are using not only their own information gathering abilities but also the social information gathered from other group members,” he says.

The study demonstrates collective knowledge, says co-author James Herbert-Read, a PhD student on the project. As long as the information is shared throughout the group and the information transfer is quick, larger groups can make both fast and accurate decisions.

Group communication leads to accurate decisions

It becomes obvious then, he says, that social communication in groups can bring out the best in individuals and helps them to make faster and more accurate decisions.

The benefits of group decision making depends on the species. Ashley’s study is the first to show that larger groups make faster and more accurate decisions but it is speculated that animals living in a relatively uncluttered environment, such as bird flocks in open skies, herds of mammals and many aquatic habitats also use the same social gathering methods.

Professor Stephen Simpson, also at the University of Sydney but not involved in the research, calls the work a “beautifully elegant experimental study which helps us understand how social groups make collective decisions based on the behaviour of their individual members.”

Ashley now plans to test the communication between the individuals who firstly notice the threat, and how the information gets transmitted across the group.

The study was published recently in the Proceedings of the National Academy of Sciences.