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Norway Lemming - Lemmus lemmus
Topic Started: Jul 3 2012, 07:56 AM (2,460 Views)
Elephantus
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Norway Lemming - Lemmus lemmus

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Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Rodentia
Superfamily: Muroidea
Family: Cricetidae
Subfamily: Arvicolinae
Genus: Lemmus
Species: Lemmus lemmus

The Norway lemming is a common species of lemming found in northern Scandinavia and adjacent areas of Russia. It is best known for its greatly fluctuating population cycles.

Habitat
This lemming is found primarily in Scandinavian countries. It is the only vertebrate species endemic to the region.

The Norway lemming dwells in tundra and fells, and prefers to live near water.

Description
The Norway lemming is one of the most colorful rodents, but aside from that, is a typical member of Arvicolinae. It has a bold pattern of black and yellow-brown, which is variable between individuals. It grows to a size of 155 mm (6 in). The tail is very short, about 10 - 19 mm.

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Ecology
Adults feed primarily on sedges, grasses and moss. They are active at both day and night, alternating naps with periods of activity.

The Norway lemming has a dramatic 3-4 year population cycle, in which the species' population periodically rises to unsustainable levels, leading to high mortality, which causes the population to crash again. This abrupt fluctuation, also found in related species, has given rise to the myth of lemming mass suicide.

The Norway Lemming spends the winter in nests under the snow. When the spring thaws begin and the snow starts to collapse, Norway Lemmings must migrate to higher ground where the snow is still firm enough for safety, or, more commonly, to lower ground, where they spend the summer months[citation needed] . In autumn, they must time their movement back to sheltered higher ground carefully, leaving after there is alpine snow cover for them to burrow and nest in, and before the lowlands are made uninhabitable by frost and ice.

Being solitary creatures by nature, the stronger lemmings drive the weaker and younger ones off long before a food shortage occurs. The young lemmings disperse in random directions looking for vacant territory. Where geographical features constrain their movements and channel them into a relatively narrow corridor, large numbers can build up leading to social friction, distress, and eventually a mass panic can follow, where they flee in all directions. Lemmings do migrate, and in vast numbers sometimes, but the deliberate march into the sea has yet to be verified.

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Reproduction
When the seasons are particularly good—short winters without unexpected thaws or freezes, and long summers—the Norway Lemming population can increase explosively: they reach sexual maturity less than a month after birth, and breed year-round if conditions are right, producing a litter of six to eight young every three to four weeks.


Edited by Taipan, Jul 3 2012, 10:48 PM.
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Elephantus
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Global Warming Threatens Lemmings in Norway

Kate Ravilious
for National Geographic News
November 5, 2008



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Climate change may be responsible for shrinking lemming populations in Norway, a new study shows.

As a result, the lack of the small mammals is cascading through the ecosystem, forcing predators to find different food sources.

Lemming populations throughout Scandinavia tend to explode naturally every three to five years, causing huge numbers to go in search of food.

Occasionally this leads the rodents to jump into water and swim to new pastures—the origin of the myth that lemmings commit mass suicide.

When lemmings boom, they're hard to miss. Norwegians have had to use snowplows to clear the squashed rodents off the roads.

In recent years, however, outbreaks have become a rarity in many parts of Scandinavia.

Kyrre Kausrud, a professor at the University of Oslo in Norway, and his colleagues analyzed lemming boom-bust cycles since 1970 for one site in southern Norway. Their findings are reported tomorrow in the journal Nature.

The data revealed that lemmings in this region have not had a population explosion since 1994.

Climate data collected over the same period suggest that warmer temperatures can explain why the rodents' numbers have remained low for more than a decade.

During the winter lemmings live in tunnels under the snow. Warmth from the Earth melts some of the snow near the ground, providing pockets of air and access to food such as moss.

Rather than remaining below freezing for most of the winter, temperatures have bounced above freezing a number of times, melting and then refreezing the snowpack.

"This enables water to enter the system, flooding the snow tunnels and then forming ice layers on the ground," Kausrud said.

Many lemmings drown when their burrows are flooded, and those that survive often starve when their food is trapped under an icy layer.

The team's data showed that lemming population explosions were linked to years with colder winters, providing the ideal snow conditions for lemmings to thrive.

They also showed that winters in southern Norway have been warmer since 1994, preventing females from rearing the large broods that lead to lemming outbreaks.

"Their findings present a convincing demonstration of the effects of climate change on lemmings and their wider ecosystem," said Tim Coulson, a population biologist from Imperial College London who was not involved with the study.

Studying census data on animals, Kausrud and his colleagues demonstrated that the lemming scarcity is also affecting the greater ecosystem.

Unable to gorge themselves on lemmings every few years, predators like the Arctic fox and snowy owl have had to rely on other food sources, such as ptarmigan (a kind of grouse) and willow grouse.

As a result, the numbers of these ground-nesting birds have been diminishing. "Lemming population explosions help to take the pressure off ptarmigan and willow grouse," Coulson explained.

Although the study looks only at one region in Norway, Kausrud and his colleagues believe the effect could be widespread.

"We might indeed expect similar changes across Scandinavia and in [Canada and Alaska]" said study co-author Nils Stenseth, also of the University of Oslo.

Kausrud and his colleagues think that it is unlikely that climate change will drive lemmings to extinction, but the impact on the ecosystem could be severe.

"As competitive relationships change for predators, prey, and plants, the whole community changes," he said.


Link: http://news.nationalgeographic.com/news/2008/11/081105-fewer-lemmings.html
Edited by Elephantus, Jul 3 2012, 08:02 AM.
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