The case of the shrinking sheep

Guest blogger Ivy Joeva explains how global warming is making one woolly species a little bit smaller.

Fri, Jul 03 2009 at 1:17 AM EST

Photo: Arje Cahn/Flickr

NOTE: This is a post by guest blogger Ivy Joeva of EcoMatters and Current TV.

In Scotland, a certain breed of wild sheep is shrinking ... and the culprit is climate change, according to a recent report in the journal Science. Typically, we would expect each new generation of sheep to be bigger than the last, since classic evolutionary theory gives the stronger, larger animals a greater chance of surviving and reproducing. But climate change is changing this picture.

On the island of Hirta, scientists have been studying the Soay sheep for over two decades. During this time, they've watched the sheep become 5 percent smaller, by measures of weight and leg height. Because there are only sheep and vegetation on this remote island, it provides researchers the ideal opportunity to understand this phenomenon ... and they've pinpointed global warming as the cause.

The winters on Hirta are becoming milder, allowing grass to grow for more of the year. "Survivial conditions are not so challenging -- even the slower growing sheep have a chance of making it, and this means smaller individuals are becoming increasingly prevalent in the population," says lead researcher Tim Coulson of Imperial College London.

The environment is actually trumping natural selection, and the team of researchers expects the trend to continue. "But," says Coulson, "it's too early to say if, in 100 years, we will have chihuahuas herding pocket-sized sheep."

via: Scientific American