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The real social network: larger social groups make faster and more accurate decisions



25 January 2011

Turns out social networking is not just a fun way to fill time - it can also be life saving. New research led by Associate Professor Ashley Ward, in the School of Biological Sciences at the University of Sydney, shows for the first time that larger social groups make faster and more accurate decisions. This crucial benefit may have been important in promoting the evolution of sociality, a strategy used by a huge variety of animals from ants to humans.

The study, published in the prestigious US journal Proceedings of the National Academy of Sciences, presented mosquitofish, Gambusia holbrooki, with a choice to swim down one of two arms in a Y-shaped channel. One arm contained a replica predator, while the other arm did not. Associate Professor Ward, with PhD student James Herbert-Read and other colleagues, found that larger groups of mosquitofish made the correct decision to swim down the predator-free arm more rapidly than smaller groups and individuals.

Associate Professor Ashley Ward and his PhD student James Herbert-Read, from the School of Biological Sciences, have shown for the first time that larger social groups make faster and more accurate decisions. This crucial benefit may have been important in promoting the evolution of sociality.
Associate Professor Ashley Ward and his PhD student James Herbert-Read, from the School of Biological Sciences, have shown for the first time that larger social groups make faster and more accurate decisions. This crucial benefit may have been important in promoting the evolution of sociality.

"Social animals are frequently required to make collective decisions about such things as the timing and direction of group travel, the detection and avoidance of predators, or the location of food. We predict that groups of animals are more accurate in their decision making than individuals," said Associate Professor Ward.

"In our study, we put animals in a really straightforward decision-making situation, where they could choose one of two options: one of which is 'wrong' and the other 'right'. The wrong decision is to swim down the arm of the Y maze where a predator is concealed; the right decision is to take the alternative path," explained Associate Professor Ward.

"Even though we used a replica predator, the fish couldn't be certain of that - from a distance it looked like a predator. It's better to be cautious and avoid something that might represent a threat, if you are able to detect that threat in the first place."

Using this set-up, the team investigated the two key parameters of decision-making: speed and accuracy.

"An optimal decision must be both fast and accurate. An accurate decision that is slow may be good in some respects, but if a predator is around, it might come too late. Similarly, a rapid but inaccurate decision is clearly far from ideal," said Associate Professor Ward.

The team tested the decision making speed and accuracy of mosquitofish in the Y maze as singles, pairs, or in groups of four, eight or 16.

"What we found is that as group size increases, fish in these groups make both faster and more accurate decisions. Their decision-making becomes more and more efficient as the size of their social group increases," explained James Herbert-Read.

"Groups of eight and above showed almost 90% accuracy, meaning that nine times out of ten they avoided the predator, whereas single fish managed only about 56% accuracy," said Mr Herbert-Read.

"Remarkably, we found that improvements in accuracy start even in groups of two fish and then accelerate rapidly.

"In addition, the fish in the larger groups typically made their decision in less than half the amount of time than that taken by fish on their own."

Why did the mosquitofish do so much better at avoiding predators in groups compared to when by themselves?

"The answer seems to lie in the greater vigilance of animals in groups and their correspondingly greater ability to detect a threat. In addition to this, once one individual has spotted the threat, the information is transmitted rapidly throughout the group. We don't know exactly how they communicate this - we assume it is to do with their behaviour, which may change once they detect a potential threat," said Associate Professor Ward.

So while fish on their own may often have simply failed to detect the threat, leading to their overall lack of accuracy, larger groups were extremely good at detecting the threat, acquiring and using the available social information and ultimately avoiding the predator.

"We haven't seen any previous studies that examine how decision making efficiency - that is both speed and accuracy of decision making - changes with group size in any animal, so this finding that fish living in groups benefit from these dramatic improvements is a first," said Associate Professor Ward.

"Given that so many animals of all different kinds live in groups, we speculate that this crucial benefit may have played an important role in the evolution of sociality."

Read the full paper in Proceedings of the National Academy of Sciences at: www.pnas.org/content/early/2011/01/14/1007102108.abstract

Watch Associate Professor Ashley Ward talk about his research on ABC's Catalyst at: www.abc.net.au/catalyst/stories/2867497.htm


Contact: Katynna Gill

Phone: 02 9351 6997

Email: 0a02030e2638567800080528703f4b3001154858230a00652518