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Originally published in Science Express on 2 July 2009
Science 24 July 2009:
Vol. 325. no. 5939, pp. 464 - 467
DOI: 10.1126/science.1173668
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Reports

The Dynamics of Phenotypic Change and the Shrinking Sheep of St. Kilda

Arpat Ozgul,1 Shripad Tuljapurkar,2 Tim G. Benton,3 Josephine M. Pemberton,4 Tim H. Clutton-Brock,5 Tim Coulson1,*

Environmental change, including climate change, can cause rapid phenotypic change via both ecological and evolutionary processes. Because ecological and evolutionary dynamics are intimately linked, a major challenge is to identify their relative roles. We exactly decomposed the change in mean body weight in a free-living population of Soay sheep into all the processes that contribute to change. Ecological processes contribute most, with selection—the underpinning of adaptive evolution—explaining little of the observed phenotypic trend. Our results enable us to explain why selection has so little effect even though weight is heritable, and why environmental change has caused a decline in the body size of Soay sheep.

1 Department of Life Sciences, Imperial College London, Silwood Park, Ascot, Berkshire SL5 7PY, UK.
2 Department of Biology, Stanford University, Stanford, CA 94305-5020, USA.
3 Faculty of Biological Sciences, University of Leeds, Leeds LS2 9JT, UK.
4 Institute for Evolutionary Biology, University of Edinburgh, Kings Buildings, West Mains Road, Edinburgh EH9 3JT, UK.
5 Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK.

* To whom correspondence should be addressed. E-mail: t.coulson{at}imperial.ac.uk

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