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Effective leadership and decision-making in animal groups on the move


For animals that forage or travel in groups, making movement decisions often depends on social interactions among group members1,2. However, in many cases, few individuals have pertinent information, such as knowledge about the location of a food source3,4, or of a migration route5,6,7,8,9. Using a simple model we show how information can be transferred within groups both without signalling and when group members do not know which individuals, if any, have information. We reveal that the larger the group the smaller the proportion of informed individuals needed to guide the group, and that only a very small proportion of informed individuals is required to achieve great accuracy. We also demonstrate how groups can make consensus decisions, even though informed individuals do not know whether they are in a majority or minority, how the quality of their information compares with that of others, or even whether there are any other informed individuals. Our model provides new insights into the mechanisms of effective leadership and decision-making in biological systems.

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Figure 1: Group accuracy, and shape, as a function of the proportion of informed individuals p, for different group sizes N.
Figure 2: The influence of the weighting of preferred direction.
Figure 3: Collective selection of group direction when informed individuals differ in preference.
Figure 4: Discrimination between two directions (s1 = 0; s2 = 100 degrees) based on information quality (χ, see Methods).

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I.D.C. thanks the Pew Charitable Trusts, the NSF and the EPSRC for their support. I.D.C. and J.K. acknowledge an EPSRC grant and are also grateful for fellowships at the Centre for Interdisciplinary Research, University of Bielefeld, where we had the opportunity to develop this research. S.A.L. acknowledges support from the NSF and the Andrew W. Mellon Foundation, and N.R.F. from the EPSRC and the BBSRC. I.D.C. thanks Balliol College for support and S. Pratt, D. Rubenstein, D. James and A. Ward for their input.

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Correspondence to Iain D. Couzin.

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Supplementary information

Supplementary Figure 1

This figure shows the influence of imperfect information on the relationship between weighting ω and the accuracy of groups and the proportion of groups that split (a), and the proportion of informed individuals p and accuracy and proportion of splitting (b). (DOC 156 kb)

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Couzin, I., Krause, J., Franks, N. et al. Effective leadership and decision-making in animal groups on the move. Nature 433, 513–516 (2005).

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