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Group decision-making in animals


Groups of animals often need to make communal decisions, for example about which activities to perform1, when to perform them2,3,4,5,6,7,8,9 and which direction to travel in1,6,7; however, little is known about how they do so10,11,12. Here, we model the fitness consequences of two possible decision-making mechanisms: ‘despotism’6,7,10 and ‘democracy’1,6,7,10. We show that under most conditions, the costs to subordinate group members, and to the group as a whole, are considerably higher for despotic than for democratic decisions. Even when the despot is the most experienced group member, it only pays other members to accept its decision when group size is small and the difference in information is large. Democratic decisions are more beneficial primarily because they tend to produce less extreme decisions, rather than because each individual has an influence on the decision per se. Our model suggests that democracy should be widespread and makes quantitative, testable predictions about group decision-making in non-humans.

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We thank J. Soeding, D. Waxman and H. Kokko for comments on an earlier version of the model, and H. Prins and M. Manser for help with accessing references. L.C. was supported by a Royal Society University Research Fellowship.

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Correspondence to L. Conradt.

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Supplementary Information: This file contains mathematical details of a model of decision-making in animals. The model predicts the fitness consequences of two types of decision-making mechanism: 'despotism', in which a single individual makes the decision, and 'democracy', in which the decision taken is that of a majority of group members. The decision being modelled is that of when to stop engaging in a particular activity ('activity synchronisation'). Information in the file relates to: (1) cases in which activity synchronisation costs do not increase linearly with the difference between a member's optimal activity duration and the group's realised activity duration; (2) cases in which activity synchronisation costs are not symmetrical (i.e., stopping an activity too early is more or less costly than stopping too late; and (3) the cost, to a despot, of coercing other group members into accepting its decision. (DOC 76 kb)

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Conradt, L., Roper, T. Group decision-making in animals. Nature 421, 155–158 (2003).

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