Global Warming is Shrinking the Soay Sheep of Scotland


Photo: Wikipedia, CC
The Incredible Shrinking Sheep!
Could the changing climate be shrinking animals? That seems to be the case for the Soay sheep of Scotland. "The island of Hirta, on the western coast of Scotland, is home to a special breed of sheep. Soay sheep, named after a neighbouring island, are the most primitive breed of domestic sheep and have lived on the isles of St Kilda for at least a millennium." These sheep are already smaller on average than other breeds of sheep, but according to a recent study, they have been getting even smaller...

Photo: Wikipedia, CC
Ed Yong of ScienceBlogs writes:

The reasons behind this downward trend have now been revealed by a group of British scientists led by Arpat Ozgul from Imperial College. Using decades' worth of data, the team showed that natural selection normally favours larger sheep, as the odds of survival increase with body size. But this evolutionary pressure has been overwhelmed by the effects of climate change. [...]

But why are the sheep growing more slowly than they used to? Ozgul says that the answer is climate change. The growth of the Soay sheep turned out to be very sensitive to shifting climate. Since 1980, winters on Soay Island have become warmer, milder and shorter, and grass grows for more of the year. As a result, lambs spend less time depending on their stores of fat for survival, and they have more food to graze on when winter ends.

The result is a more forgiving climate, where even lambs that grow slowly make it past their first year. Compared to earlier generations, these newborns have an easier time of it and they don't need to put on as much weight in their first few months. Whereas in the past, only the largest and fastest-growing lambs would make it to breeding age, now even the slackers can get away with it. Climate, then, is the culprit behind the mystery of Scotland's shrinking sheep.

Global Warming Effects
Of course we knew that the changing climate had an impact on animals, but we usually talk about extinction or migration, rarely about these types of physiological changes. It's one more thing to look for. Some changes might be benign, but some might lead to dramatic outcomes. We must especially be careful about changes that look benign at first but that could lead to big problems a few decades out (for example, a species could get progressively less well adapted to harsh winters, until a freak winter wipes out most of it and leaves behind a diminished population that isn't viable)...

Via ScienceBlogs
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