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.
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
