Call it the case of the shrinking sheep. On the remote Scottish island of Hirta, sheep have been getting smaller, shrinking an average of 5% over the last 24 years. Don't blame evolution, though. Researchers say climate change is the real culprit.
The Hirta sheep belong to a breed known as Soay, after the remote Scottish island where they arose. One of the most primitive forms of domestic sheep, Soays first came to Hirta in 1932. Because Hirta is a remote island, its sheep have remained genetically isolated, and no other sheep have been brought in for breeding. That's made Hirta's Soays ideal subjects for scientific study.
In 2007, scientists first reported that the sheep were smaller than they had been in the past. This prompted biologist Arpat Ozgul of Imperial College London and colleagues to analyze body weight data going back 24 years. The researchers confirmed that the Soays had indeed been getting smaller. And, as they report online today in Science, the reason appears to be climate change.
In the past, Hirta's sheep gorged on grass during their first summer, the team notes, piling on the weight in order to make it through the island's typically harsh winters. But over the past quarter-century, Hirta has had unusually short and mild winters. As a result, Ozgul and colleagues propose, grass has become available for more months of the year, meaning the Soay sheep do not have to bulk up as much. In addition, Hirta's harsh winters used to kill small ewes born to young mothers. But now these small ewes survive--and because of their low birth weight, they never get as big as normal sheep. That drives down the average size of the entire population, the team reports. Further mathematical modeling allowed the researchers to propose that natural selection has played little--if any--role in the shrinkage of the Hirta sheep.
Malcolm Gordon, an ecologist and evolutionary biologist at the University of California, Los Angeles, praises the study. But he says that other mechanisms may be at work. "Changing [environmental] conditions on the island ... [may] have led to changes in the chemical composition and nutritional value of the plant foods the sheep eat," he says, and that may have shrunk the sheep. Though at the end of the day, he says, climate change could still be the root cause.
This account from ScienceNow, although even it has some problems in its reporting, is light years better than that given by USA Today. When I coupled this with a small story from this week's Economist I actually got a pretty good overview of the research. As I suspected the trouble with the USA Today story had more to do with their stupidity rather than the researchers.
For starters, the researcher did in fact check for other factors affecting weather in the region, including the North Atlantic Oscillation. USA Today probably didn't know what the NAO was so they left that out. Furthermore, the researchers did not, as USA Today claimed, use computer modelling to blame climate change for shrinking sheep sizes, but in fact only used it to rule out the effects of natural selection (which makes sense given we are only talking about 25 years here.)
Furthermore, the Economist made it clear that these were wild reproducing sheep (which even ScienceNow missed as being important), which is important as it limits the potential impact of human beings on the sheep.
USA Today, which is probably the most political of the Anthropogenic Global Warming crowd, has ceased to be a news source for me. They blatantly either misrepresented this research or they were too stupid to understand it. Either way they do not deserve to be read. I will be removing them from my Bloglines lineup, and I suggest you avoid them from now on as well.
I guess this proves not all reading is a good thing.
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