Fish Choosy About Who They Follow

Wednesday, May 14, 2008

Research by Dr Ashley Ward, from the School of Biological Sciences has shown for the first time in vertebrates just how strong the desire to follow a leader can be in animals that are alone compared to those in a group.

Using a replica fish, Dr Ward was able to lure solo fish of the same species around the tank and into potentially dangerous situations, such as swimming close to predatory fish.

However, when the test fish were put in larger groups of the same species, they were able to ignore the replica fish leading them to danger, only starting to take notice when there was more than one leader.

The need for social conformity exerts an extremely powerful influence on the behavior of social animals - from fish to sheep to humans - sometimes seemingly regardless of cost.

"The results show that an isolated member of a social species will pay almost any cost to stick close to a member of the same species, but once they're in a group they're able to ignore that individual if it tries to lead them into danger," said Dr Ward.

"The decision of whether to follow the lead of another individual is a fundamental problem for grouping animals. Leadership in an animal social group may be assumed by an individual or individuals who have extra information about the habitat - the leader may have spotted food or a predator - and moves towards or away from it accordingly," explained Dr Ward.

"Other animals in the group have to decide whether to follow the reaction of this leader. Following can be really beneficial if the leader is right, but 'blind copying' can be dangerous. So group members have to be choosy about who they follow."

So how do animals use the behavior of others to make more accurate movement decisions, especially when it isn't possible to identify which individuals possess pertinent information?

"One plausible answer is that animals in groups only respond when they see a threshold number of fellow group members perform a particular behavior. Our research examined the difference between groups of fish and solo fish, in whether they could be led by replica models of the same species, both in a neutral and in a potentially dangerous situation - past a model of a predatory fish," said Dr Ward.

"We confirmed that the model of the predatory fish was regarded as a threat by the test fish in control experiments, where test fish showed a strong aversion to the predator model.

"Despite this, solitary test fish would follow a replica leader towards the predator model, but when test fish were in larger groups of four or eight, the picture was very different: the solitary replica leader was ignored. We found it required two to three replica leaders to influence these larger groups," said Dr Ward.

The 'quorum response': further applications

The effect has been named the 'quorum response' - just like the fixed number of people required to be present in a human committee or legislative assembly before the members can conduct valid business.

"By adopting the quorum response - only following when a threshold number of individuals behave in a particular way - animals can reduce the likelihood of spreading disadvantageous behavior. While a single animal may act irrationally, it's far less likely that several individuals will act strangely at the same time."

So the quorum response may filter out maverick behavior, but allow animals to benefit from following behavior in groups.

"Our new research is important because these types of responses have been shown in invertebrates, like ants, bees and cockroaches, but this is the first time that it has been shown in vertebrate animals. The quorum decision rule is simple, but extremely effective, and it has important implications for human decision making.

"We used fish because they're easy to work with, but people are more similar to them in our decision making than we may choose to admit!"

The research appears in the current issue of Proceedings of the National Academy of Sciences.

Source: University of Sydney

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Time Stamp: 5/14/2008 at 2:21:15 PM UTC