Like a Wool Sweater, Scottish Sheep Shrink As Climate Heats Up

By Allison Bond | July 2, 2009 5:15 pm

Scottish sheepDon’t be alarmed, but on a remote island in Scotland the sheep are shrinking.

Instead of gradually increasing in size as expected due to evolution, the average weight of the wild sheep has decreased as average temperatures heat up. The discovery shows that a species’ response to global warming can be unpredictable, and can be based on multiple factors. According to a study published in Science, warmer and wetter winters have made it easier for smaller sheep to survive the hard months and go on to bear offspring, thus passing these “small” genes onto the next generation of sheep.

Since 1985, the average weight of the wild Soay sheep living on the island of Hirta has decreased by about 5 percent. Due to global warming, the winters on the Scottish isles are becoming becoming shorter and milder. That makes food more abundant and allows some of the smaller, more vulnerable and younger sheep to survive. Then they go on to have offspring that tend to be small themselves — and have a better chance of survival because of the increasingly mild winters. “The environmental and evolutionary processes are intertwined. There’s still natural selection, but it’s not leaving as big a signature as it used to. There’s still a disadvantage to being small, but not as much” [Time], says lead researcher Tim Coulson.

There’s another factor that also influences the average size of sheep in the flock, one that scientists call the “young mum” factor. Because sheep bear offspring at a young age relative to other mammals, and because the size of the mother sheep limits the size of the lamb she can carry, lambs born to yearling ewes instead of fully grown sheep weighed less at birth than their mothers did and remained smaller throughout their lifetimes [Los Angeles Times]. That effect didn’t account for the entire decrease in average weight, but when combined with the effects of milder winters, the researchers came up with a decrease in size that correlated well with the actual decline shown by the data.

The somewhat counterintuitive decrease in the sheep’s average size demonstrates the unexpected effects the changing climate may already be having on today’s species. Classic evolutionary theory would predict that wild sheep gradually get bigger, as the stronger, larger animals survive into adulthood and reproduce… The team says this shows the “subtle interplay” between evolution and the environment [BBC News]. The scientists hope to use the data and methods they’ve amassed to produce a model to predict future changes in the size of sheep in the flock.

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80beats: Hunting Big Game Speeds Evolution of Shrinking Species
80beats: Global Warming Threatens Tropical Species, Too

Image: A. Ozgul / Science / AAAS

CATEGORIZED UNDER: Environment, Living World
  • Gerald Fredriksen

    Have you idiots ever heard of the Shetland islands or the “hobbit” fossil? It is common knowledge that animals on small isolated islands tend to decrease in size. This is another desperate attempt by the global warming nuts. There is no evidence that shows a clear causal relationship between global warming and human activity.

  • Don Glenn

    Ewe people should know better. Are all your articles so stupid? So in a 1000 years these sheep will be the size of rats?

  • Christina Viering

    Does this mean smaller sweaters?

  • Anatomy Science Fair Projects

    This story has been heating up discussion boards. It is very interesting that the sheep seem to be shrinking, but the cause of the size change most likely is not directly related to global warming. Rather it is more likely that food supply and the conditions of the local ecosystem make it more advantageous to be smaller in stature. The shrinking effect is a common phenomenon for populations of animals that have been isolated on an island. Other examples include a group pygmy mammoths that were found on an island off the coast of California, and several pygmy horse populations found on islands in Northern Europe.

  • Don Glenn

    Not only smaller sweaters but also smaller wool caps to protect the tiny brains of the global warming nuts.

  • Nick

    Wow, when did the comment section turn into such a trollfest?

    It’s easy to make all sorts of wild claims, but if you don’t have any reference material to back up this “common knowledge,” your opinion is scientifically invalid.

    And if evolution only favored large animals, we’d all be huge by now, wouldn’t we? It’s not like tiny species evolved out of nowhere recently, they too have 100,000,000 years of evolution behind them. So being larger isn’t necessarily advantageous. It all depends on the conditions you live in, the source of natural selection.

    There’s plenty of evidence that says gravity works as a force over distance, but no known physical property of the universe that we’ve discovered so far that explains it. We don’t need a direct causal link between man’s activities and what is happening on the planet – we are the dominant species, and like all dominant species we affect the environments we live in. We just happen to be a semi-cohesive global whole reversing millions of years of carbon sequestration. Carbon is known to warm the air, and has done so in direct proportion to the amount humanity has put into it. Quid pro quo.

  • edwren

    Absolute nonsense.

  • nemski

    Boy, I was stopping by just to say nice headline.

    What amazes me about the trolls is the amount of time they spend posting to blogs where their viewpoint is ignored.

  • colourful_thoughts

    so true nemski.

  • Morgan-LynnGriggs Lamberth

    Gee, Obama-Biden are counting on green and energy projects to spur entrepreneurs to help counter climate change and thereby produce more jobs. I’m with them!
    Climate change denialists don’t have the spirit of us skeptics who demand evidence rather than the argument from incredulity of the denialists.

  • shaking head

    all i can say is wow… i cant belive people still havent come to terms with the planet is warming.. and not only that.. humans (Us for any of you who werent sure) are causing global warming by releasing greenhouse gasses..

  • ME

    I honestly couldn’t believe what I was reading. Obviously the sheep are affected by their environment. If warmer climates have caused an increase of food on the island, shouldn’t the sheep population increase in general, making the 5% decrease in size more of a horizontal adjustment and less of an evolutionary drop? All this article is really saying is that the sheep are doing well, unless they have large natural predators. Maybe, to buffer the effects of global warming, which we know to be caused by humans, we should open up a Hirta island hunting season for small sheep to “naturally select” the bigger ones. I’ll write that proposal to the scottish government up asap.

  • Trevor J Wallace

    Why is it the naysayers are so quick to call those of us worried about our planets “idiots” (and that’s fairly mild compared to some of the language I’ve heard and had cast in my direction)? Everyday the evidence of global warming mounts and everyday “denialists” are converted to the truth. And before anyone brings up the cliche, “you can fool some of the people…”, there are no fools here. Except the ones calling us idiots. Oops, I just name-called, didn’t I?

    And kudos to Morgan-LynnGriggs Lamberth. We do indeed rely on facts and evidence – far more than the ones denying our impact on the globe.

  • Jumblepudding

    I believe that these sheep are operating under the misapprehension that they are birds. Notice they do not so much fly as plummet. Perhaps decreasing in size shall increase their aerodynamic potential.

  • Shaithis

    Considering that this has been the coldest summer in recent memory, I imagine that those same sheep will be gigantic next year.

  • Brian

    I’m sure there’s a joke in here somewhere about Scotsmen, sheep and shrinkage!


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