A recent study, that spanned for 20 years, finds that Scottish sheep are changing their body shape and population size due to the weather patterns. The journal Science published this study which showed that there were larger sheep for the harsher winters, which affected the size of the sheep’s population. This affect however was not true for the milder winters.
An author and scientist, Tim Coulson, states “Until now, it has proven really quite difficult to show how ecology and evolutionary change are linked, but we have developed a way to tie them together,”
Soay sheep on the island of Hirta in the Outer Hevrides was the sheep population that Dr. Coulson and his colleagues examined for the study.
“The reason we looked at these sheep is they have been studied in enormous detail. Where they live is like a natural laboratory – it is a really simple system – there is just sheep and grass on the island,” explained Dr Coulson.
The data for the study has been recorded since 1985 and focused on the body measurements of the sheep as well as their population.
“To determine how ecology influences evolution and vice versa, an important step is to be able to see how population dynamics are influenced by traits such as body size or eye color that are, in part, controlled by genes.”
When there were a lot of large sheep that came into the sheep’s population, the population would increase which in turn linked sheep body size to reproductive success. This interested the researches because they discovered that the sheep’s body size was being influenced by the environment they lived in.
If there was a bad winter the larger sheep were the ones that survived. Thus the overall population would increase with young sheep that were on the larger size.
“But over the years, winters have been getting a little bit better; and as winters have got better, we have found there is not as much natural selection for large animals as we saw in the past, as there is less advantage to being big.”
As long as the weather does not prohibit the survival of the small sheep there won’t be dramatic body size increased among the sheep. Therefore as long as the winters remain mild there will be little change in the average sheep size, because there isn’t a lot of need for natural selection.
Coulson added “People have argued for a long time that climate change is leaving an ecological legacy, but we have shown it will leave an evolutionary legacy too,”