Journal of Theoretical Biology, 2002, 218,
1-11.
Collective memory and spatial sorting in animal
groups
Iain D. Couzin *†‡ , Jens Krause * , Richard James
§ , Graeme D. Ruxton ¦ and Nigel R. Franks ¶
* Centre for Biodiversity and Conservation, School of Biology, University
of Leeds, Leeds LS2 9JT, UK; § Department of Physics, University
of Bath, Bath BA2 7AY, UK; ¦Division of Environmental and Evolutionary
Biology, Graham Kerr Building, University of Glasgow, Glasgow G12 8QQ,
UK; ¶ Centre for Behavioural Biology, School of Biological Sciences,
University of Bristol, Bristol BS8 1UG, UK; ‡ Current address:
Department of Ecology and Evolutionary Biology, Princeton University,
Princeton, NJ 08544, USA.
‡ author for correspondence: icouzin@princeton.edu
We present a self-organising model of group formation
in three-dimensional space, and use it to investigate the spatial dynamics
of animal groups such as fish schools and bird flocks. We reveal the
existence of major group-level behavioural transitions related to minor
changes in individual-level interactions. Further, we present the first
evidence for collective memory in such animal groups (where the previous
history of group structure influences the collective behaviour exhibited
as individual interactions change) during the transition of a group
from one type of collective behaviour to another. The model is then
used to show how differences among individuals influence group structure,
and how individuals employing simple, local rules of thumb, can accurately
change their spatial position within a group (e.g. to move to the centre,
the front, or the periphery) in the absence of information on their
current position within the group as a whole. These results are considered
in the context of the evolution and ecological importance of animal
groups.
