Featured Research

from universities, journals, and other organizations

Climate Change And The Mystery Of The Shrinking Sheep

Date:
July 4, 2009
Source:
Imperial College London
Summary:
Milder winters are causing Scotland's wild breed of Soay sheep to get smaller, despite the evolutionary benefits of possessing a large body, according to new research.

Milder winters are causing Scotland's wild breed of Soay sheep to get smaller, despite the evolutionary benefits of possessing a large body.
Credit: iStockphoto

Milder winters are causing Scotland's wild breed of Soay sheep to get smaller, despite the evolutionary benefits of possessing a large body, according to new research.

The new study provides evidence for climate change as the cause of the mysterious decrease in the size of wild sheep on the Scottish island of Hirta, first reported by scientists in 2007. The researchers believe that, due to climate change, survival conditions on Hirta are becoming less challenging, which means slower-growing, smaller sheep are more likely to survive the winters than they once were. This, together with newly-discovered so-called 'young mum effect' whereby young ewes produce smaller offspring, explains why the average size of sheep on the island is decreasing.

Classical evolutionary theory suggests that over time the average size of wild sheep increases, because larger animals tend to be more likely to survive and reproduce than smaller ones, and offspring tend to resemble their parents. However, among the Soay sheep of Hirta, a remote Scottish island in the St Kilda archipelago, average body size has decreased by approximately 5% over the last 24 years.

The research team analysed body size and life history data, which records the timing of key milestones throughout an individual sheep's life, for Soays on Hirta over this 24 year period. They found that sheep on the island are not growing as quickly as they once did, and that smaller sheep are more likely to survive into adulthood. This is bringing down the average size of sheep in the population over all.

Professor Coulson suggests that this is because shorter, milder winters, caused by global climate change, mean that lambs do not need to put on as much as weight in the first months of life to survive to their first birthday as they did when winters were colder.

He explains: "In the past, only the big, healthy sheep and large lambs that had piled on weight in their first summer could survive the harsh winters on Hirta. But now, due to climate change, grass for food is available for more months of the year, and survival conditions are not so challenging - even the slower growing sheep have a chance of making it, and this means smaller individuals are becoming increasingly prevalent in the population."

Their results suggest that the decrease in average body size seen in Hirta's sheep is primarily an ecological response to environmental changes over the last 25 years; evolutionary change has contributed relatively little.

In addition, the research team also discovered that the age at which a female sheep gives birth affects the size of her offspring. They realised that young Soay ewes are physically unable to produce offspring that are as big as they themselves were at birth. This 'young-mum' effect had not been incorporated into previous analyses of natural selection, which explains in part why the sheep of Hirta are defying biologists' expectations.

"The young mum effect explains why Soay sheep have not been getting bigger, as we expected them to," concludes Professor Coulson, "But it is not enough to explain why they're shrinking. We believe that this is down to climate change. These two factors are combining to override what we would expect through natural selection."

The research was carried out in collaboration with scientists from the Universities of Leeds, Cambridge, Edinburgh and Stanford. It was funded in the UK by the Natural Environment Research Council (NERC).


Story Source:

The above story is based on materials provided by Imperial College London. Note: Materials may be edited for content and length.


Journal Reference:

  1. Arpat Ozgul et al. The Dynamics of Phenotypic Change and the Shrinking Sheep of St. Kilda. Science, July 3, 2009

Cite This Page:

Imperial College London. "Climate Change And The Mystery Of The Shrinking Sheep." ScienceDaily. ScienceDaily, 4 July 2009. <www.sciencedaily.com/releases/2009/07/090702140845.htm>.
Imperial College London. (2009, July 4). Climate Change And The Mystery Of The Shrinking Sheep. ScienceDaily. Retrieved August 21, 2014 from www.sciencedaily.com/releases/2009/07/090702140845.htm
Imperial College London. "Climate Change And The Mystery Of The Shrinking Sheep." ScienceDaily. www.sciencedaily.com/releases/2009/07/090702140845.htm (accessed August 21, 2014).

Share This




More Plants & Animals News

Thursday, August 21, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Drug Used To Treat 'Ebola's Cousin' Shows Promise

Drug Used To Treat 'Ebola's Cousin' Shows Promise

Newsy (Aug. 21, 2014) — An experimental drug used to treat Marburg virus in rhesus monkeys could give new insight into a similar treatment for Ebola. Video provided by Newsy
Powered by NewsLook.com
Terrifying City-Dwelling Spiders Are Bigger And More Fertile

Terrifying City-Dwelling Spiders Are Bigger And More Fertile

Newsy (Aug. 21, 2014) — According to a new study, spiders that live in cities are bigger, fatter and multiply faster. Video provided by Newsy
Powered by NewsLook.com
Lost Brain Cells To Blame For Sleep Problems Among Seniors

Lost Brain Cells To Blame For Sleep Problems Among Seniors

Newsy (Aug. 21, 2014) — According to a new study, elderly people might have trouble sleeping because of the loss of a certain group of neurons in the brain. Video provided by Newsy
Powered by NewsLook.com
Ramen Health Risks: The Dark Side of the Noodle

Ramen Health Risks: The Dark Side of the Noodle

AP (Aug. 21, 2014) — South Koreans eat more instant ramen noodles per capita than anywhere else in the world. But American researchers say eating too much may increase the risk of diabetes, heart disease and stroke. (Aug. 21) Video provided by AP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins