Soay sheep in the St Kilda archipelago are shrinking says a new study.

Credit: Science/AAAS

The significance of this study, Sugden said, is that it shows we are now able to tell the difference between these two different kinds of change."They've shown that ecological response to environmental variation is the major driver of these dynamics and evolutionary change has contributed relatively little."

The study is "a very good example of the value of long-term research in revealing how environmental change affects the living world ," he added.

Global warming has been found to be having a profound effect on many species, from causing some to move to higher latitudes or altitudes to track cool conditions, to altering the migration routes of others. But there have been few cases documented where climate change has yet had a direct effect on the size of an animal.

"Unfortunately it's too early to tell whether a warming world will lead to pocket-sized sheep," said Coulson.

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