November 6, 2008

Lemmings Decline In Norway Due To Global Warming

Among the growing numbers of species to be hit by global climate change, it appears that lemming populations are declining due to wetter winters in southern Norway, researchers said.

Scientists found that numbers of the animals no longer vary over a regular cycle, as they did until a decade ago.

Writing in the journal Nature, researcher Nils Stenseth of Oslo University and colleagues from Norway and France found that a reduction of lemmings was causing predators such as the Arctic fox to eat other prey including grouse and ptarmigan birds.

"The lemming population is falling and the peaks are disappearing," said Stenseth.

In boom years, lemmings are the most plentiful and important prey for these carnivores.

Lemmings use the winter season to live in the space between the ground and a stable layer of snow above.

Dry winters allow for larger numbers of lemmings to survive than wetter winters.

On occasions, there were so many that snowploughs were deployed to clear squashed animals from roads. These years often saw Norwegian lemmings (Lemmus lemmus) having to compete hard for food.

The desperate search led some to jump off high ground into water, leading to the popular - but wrong - assumption that they were prone to commit collective suicide.

Now researchers are seeing fewer years of high competition for food among lemmings, which has led them to believe that it is linked to the quality of snow.

Warmer temperatures in recent years meant snow was wetter, often turning hard and icy. That made it more difficult for rodents to hide and reach food.

Stenseth said the study showed the first evidence of weakening lemming numbers and disruptions to snowfall.

The study of lemmings since 1970 showed the last population boom was in 1994, ending a pattern of spikes every 3-5 years.

"A relatively small effect on one particular species is having a broad effect on the system," Stenseth said. In years with a lemming population boom, predators such as Arctic foxes or snowy owls used to get a valuable boost.

"Now when the lemming peak is gone...they will prey on other species such as ptarmigan and grouse," he said.


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