Skip to comments.Secret of Scotland's Shrinking Sheep Solved
Posted on 07/04/2009 2:18:03 PM PDT by neverdem
Slimming down. Sheep on the remote Scottish isle of Hirta have been getting smaller.
Credit: A. Ozgul/Science
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.
The Dynamics of Phenotypic Change and the Shrinking Sheep of St. Kilda
Environmental change, including climate change, can cause rapid phenotypic change via both ecological and evolutionary processes. Because ecological and evolutionary dynamics are intimately linked, a major challenge is to identify their relative roles. We exactly decompose change in mean body weight in a free-living population of Soay sheep into all processes that contribute to change. Ecological processes contribute most, with selectionthe underpinning of adaptive evolutionexplaining little of the observed phenotypic trend. Our results enable us to explain why selection is not realized even though weight is heritable and why environmental change has caused a decline in Soay sheep body size.
I'm bigger than either of my parents. Diet couldn't have any thing to do with it, no way. It must be man caused global warming. This is utter crap for science!
75 years of in-breeding creating more and more runt offspring.
Sheep dip! Snake Oil !
Global Warming.....!!The answer to our Obesity problem!!
And the smaller sheep who didn’t survive in the past are now surviving to adulthood. Isn’t that a good thing, that more survive because the winters aren’t as harsh????
If more sheep survive because of milder weather, then the total number of sheep-pounds and sheep-wool goes up.
I don’t see any problem here.
You nailed the real reason!
I think you should get Freepers Points for the correct answer.
I wonder if any of these jeenyuses had enough sense to do a study on what foods the sheep were eating, what were available 24 years ago and in what relative abundance versus today? I doubt if the sheep subsist on just grass. Even if they do, they are many varieties of grass. Some would be better food sources than others. I think what we are looking at here is another Kaibab waiting to happen.
“Sheep lie! Sheep lie!”
Is there poorer diet in these fields? (So only smaller survive, so sheep grow less in the same time frame?)
Is there more inbreeding?
Is there better diet - so fewer small sheep die?
Are there fewer predators, so smaller sheep can stay alive?
No answers to the above, and the above are not addresses in the article = It must be global warming!
A full 1/4 of one degree change in global temperatures in 30 years = GLOBAL CATASTROPHE! Small sheep!
Then there's no hope...soon they will be the size of rodents.
Someday Freeper Points will be worth more than US currency.
Wasn’t there research done in the past that basically shows creatures stuck on an island will grown smaller versions of themselves over time, whereas the mainland creatures will pretty much maintain normal sizing? Or am I mis-remembering?
Thanks for that. I should have read more of the responses. I was asking about insular dwarfism, but didn’t know what it was called. I just remember that I’d heard about the condition in the past.
It’s the wool. They leave them out in the rain. Everyone knows you can’t wash wool in warm water.
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