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Ecology and statistics

Nonlinear sheep in a noisy world

Nature volume 394, pages 620–621 (1998)Cite this article

Population ecologists have long been interested in two key topics1: the first is the relative importance of intrinsic factors (such as the inhibition of reproduction at high population densities) and extrinsic environmental variations in determining population fluctuations; the second is nonlinearity in the processes that generate these fluctuations. On page 674 of this issue, Grenfell and co-workers2 discuss both of these issues. From their studies of fluctuations in two populations of Soay sheep living on islands 3.5 km apart in the St Kilda archipelago (in the Outer Hebrides), they provide a new insight into the synchronization of population fluctuations at separate, but not too distant, locations3,4.

Robert May's pioneering paper of 1974 showed that even very simple, deterministic population models can have complicated dynamics (including chaos, which is not easily distinguishable from a random pattern), provided the models are sufficiently nonlinear5. This work stimulated ecologists to look for the presence of nonlinear interactions (that is, situations in which two and two do not make four). Although ecologists generally appreciate the importance of external (abiotic) environmental variability, be it deterministic or random, most ecological models of population dynamics (deriving, in one way or another, from Lotka and Volterra) are essentially deterministic1. Abiotic, random variability has been — and still is — emphasized much less. In other words, all population-dynamic variations are, by and large, seen as effects of deterministic processes.

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Authors and Affiliations

  1. the Division of Zoology, Department of Biology, University of Oslo, Blindern, N-0316, Oslo, Norway

    Nils Chr. Stenseth

  2. the Department of Statistics and Actuarial Science, University of Iowa, Iowa City, 52242, Iowa, USA

    Kung-Sik Chan

Authors
  1. Nils Chr. Stenseth
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  2. Kung-Sik Chan
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Stenseth, N., Chan, KS. Nonlinear sheep in a noisy world. Nature 394, 620–621 (1998). https://doi.org/10.1038/29177

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