Is animal behaviour chaotic? Evidence from the activity of ants

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Abstract
Chaotic dynamics have been implicated in several biological phenomena including epidemics (Olsen & Schaffer 1990), population dynamics (Schaffer & Kot 1985; Sugihara & May 1990), electroencephalograms (Mayer-Kress & Layne 1987) and certain physiological rhythms (Glass & Mackey 1988). In this paper I show that animal behaviour may also be chaotic. The attractor of the movement activity of single, isolated Leptothorax allardycei ants has a small, non-inter dimension characteristic of low-dimensional chaos. The activity of entire colonies of ants yields an integer dimension that is consistent with periodicity in activity. First-return maps of the activity of single ants are highly non-random suggesting that the interpretation of determinism in these activity patterns is realistic. By contrast the first-return maps of whole-colony activity records show no pattern, a fact consistent with the interpretation of noisy periodicity in colony activity rhythms.