Submitted on March 17, 2009
Accepted on June 19, 2009
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 Coulson 1*
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 School of Biology, 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.
Tim Coulson , E-mail: t.coulson{at}imperial.ac.uk
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 decompose change in mean body weight in a free-living population of Soay sheep into all 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 is not realized even though weight is heritable and why environmental change has caused a decline in Soay sheep body size.
