Changing climate, shrinking sheep

by John D. Cox | July 05, 2009

For centuries now, a wild breed of sheep has been grazing on the island of Hirta off the coast of northern Scotland.  Part of the St. Kilda archipelago, it is the remotest part of the British Isles, and this isolation has attracted genetic researchers to the sheep in the way the finches of the Galapagos have fascinated students of evolution since Charles Darwin visit in the 1830s.

Among the tenets of Darwin's thinking is the idea that the bigger and the stronger are the fitter, and so naturally selected to survive at the expense of the smaller and weaker.  But for at least 25 years now, something has been happening to the population of Soay sheep of St. Kilda that seems to contradict this basic idea.  Rather than larger, the sheep have been getting smaller.

In a paper published online by the journal Science, biologist Tim Coulson of Imperial College London explains it this way: "In the past, only the big, healthy sheep and large lambs that had piled on weight in their first summer could survive the harsh winters on Hirta. But now, due to climate change, grass for food is available for more months of the year, and survival 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."

- John D. Cox
Image: Imperial College London

Comments

[Cabal]

Ergo hoc, propter hoc.

This is a conclusion drawn from a single strain of evidence. Is there empirical evidence that supports the global warming change (i.e. data collection on this island which convincingly shows a deviation in the duration of the edible food availability)? Can this be directly correlated to the reduction of the size of the sheep? Can you at least show a statistically significant reversal in the trending of average size within the study???

If not, this is just bad science. Islands causing species to adapt in either smaller or larger variants is nothing new. Flores island spawned miniature humans and elephants... unless you can correlate to relevant global warming data it means nothing.

I understand Discovery blogs tend to snip out the science in exchange for an exciting headline, but you guys need to either include some facts (or at least a link!!!) or stay away from making tabloid claims.