Paco Enterprises brought my attention to this gem from Yahoo News:
WASHINGTON – Like the wool sweater that emerges from the dryer a size too small, global warming seems to be shrinking sheep.
On average, wild Soay sheep on Scotland’s island Hirta are 5 percent smaller today than they were in 1985, according to a team of researchers led by Tim Coulson of Imperial College London.
“The decrease in body size was due to a reduction in growth rates caused, in part, by the changing climate,” Coulson said in an interview via e-mail.
Evolution favors the development of large sheep, which can more easily survive harsh winters, Coulson explained. So the researchers became curious about the overall decline in size of the animals on Hirta.
They discovered that as the climate has grown milder, small lambs that would not have survived previous winters were now living to grow up and reproduce.
Since size is inherited, the survival and reproduction of these smaller animals lowered the average size of the herd.
In addition, Coulson noted, there is what he termed the “young mum effect,” with the younger mothers physically unable to produce large offspring.
The find adds to the understanding of how change occurs in many types of animals, he said, including birds, fish and mammals.
It shows how evolution and ecology each play a role in change, Coulson said: “And that, for our wild sheep at least, climate change is having a detectable effect on body size — a trait that is partly determined by genes — and that this compliments previous research showing how climate change can influence population size.”
“This study addresses one of the major goals of population biology, namely to untangle the ways in which evolutionary and environmental changes influence a species’ traits,” said Andrew Sugden, deputy and international managing editor at Science, which published the report.
The research was supported by Britain’s Natural Environment Research Council.
Apparently Britain’s Natural Environment Research Council doesn’t know that Soay are SMALL sheep. Small breed ewes generally lamb as yearlings. The birth and weaning weight of the lambs has to do with the amount of food available for the ewes.
So, let us recap:
Soay sheep are small, not large. They live on a small island with a limited amount of feed. Their population is controlled by starvation. Small sheep reach sexual maturity more quickly and lamb as yearlings (actually, my sheep have lambed before a year of age). The birth weight and weaning weight of lambs has a lot to do with the nutrition of the mother.
Just knowing those limited facts (which are not disclosed in the article), would you think that natural selection would be selecting for large sheep or smallish sheep? Would you think that an inbred population that has been selecting for small size for generations of sheep would have a tendency to be larger or smaller? Mmmmmmmm. So far, nothing to do with “global warming”.
In addition, Coulson noted, there is what he termed the “young mum effect,” with the younger mothers physically unable to produce large offspring.
And which “young mum” effect would that be? My grandmother was 13 when she married. Her first son grew to be over 6′ tall. So did her subsequent sons. I was recently reading about a group of tiny little preemies (1 lb. birthweight) that grew to normal size. The small birthweight wasn’t associated with the age of the mother.
My yearling (or younger) ewes have lambs that are about the same size as the twins that the older ewes produce. Mmmmm hmmmm, thass right, baby. Yearlings have a tendency to produce singles. Older ewes are more apt to produce twins. As the ewes age, they begin dropping singles again. If ewes are nutritionally challenged, they have a tendency to produce singles regardless of age.
Now let’s go back to the statistic casually tossed out:
On average, wild Soay sheep on Scotland’s island Hirta are 5 percent smaller today than they were in 1985, according to a team of researchers led by Tim Coulson of Imperial College London.
Really. Since there are no sheep that were around in 1985 to compare to the sheep from 2009, that is a rather tough statistic to check.
Again, let’s review:
The weight of sheep has a lot to do with their nutritional status. It also has to do with the time of year, the breeding season (rams), whether or not they are lactating (ewes) and their age. Their nutritional status has a lot to do with how many sheep are on the island. How do the sheep population numbers of 1985 and 2009 compare? What was the nutritional status of the sheep in both years? How many males to females (males are larger and heavier)? How many lambs to adult sheep? See how those averages can be massaged?
Something tells me that Britain’s Natural Environment Research Council doesn’t support any research that does not find a link to “global warming”.
