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Science 22 July 2005:
Vol. 309. no. 5734, pp. 607 - 610
DOI: 10.1126/science.1110760
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Reports

On the Regulation of Populations of Mammals, Birds, Fish, and Insects

Richard M. Sibly,1* Daniel Barker,1 Michael C. Denham,2 Jim Hone,3 Mark Pagel1

A key unresolved question in population ecology concerns the relationship between a population's size and its growth rate. We estimated this relationship for 1780 time series of mammals, birds, fish, and insects. We found that rates of population growth are high at low population densities but, contrary to previous predictions, decline rapidly with increasing population size and then flatten out, for all four taxa. This produces a strongly concave relationship between a population's growth rate and its size. These findings have fundamental implications for our understanding of animals' lives, suggesting in particular that many animals in these taxa will be found living at densities above the carrying capacity of their environments.

1 School of Animal and Microbial Sciences, University of Reading, Whiteknights, Reading RG6 6AJ, UK.
2 Statistical Sciences Europe, GlaxoSmithKline Research and Development Limited, New Frontiers Science Park, Third Avenue, Harlow, Essex CM19 5AW, UK.
3 Institute for Applied Ecology, University of Canberra, Canberra ACT 2601, Australia.

* To whom correspondence should be addressed. E-mail: r.m.sibly{at}reading.ac.uk

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