What happens to lemmings? In the seventies, a suicidal instinct so much was readily allocated them they died from exhaustion some years, to cross the Norwegian fiords in swimming. The simple effect of a cyclic overpopulation which ended up starving them. But for fifteen years, these demographic explosions practically ceased. According to jobs published in Nature last week, it is the modification of the climate from the north of Scandinavia which would explain this evolution (1).

The lemming is in principle a prolific animal. He lived three-four years, but every female can give birth to three ranges a year, with up to twelve babies to each! Regularly, every three-five years, the demography of the rodent blew up therefore to the point where it was necessary to sometimes clear away the Norwegian roads in the snowplow to remove bodies crushed on the bitumen. Then, for lack of food, the animals threw themselves into a hopeless hunt, not hesitating to cross fiords and rivers. An often fatal trip But here for fifteen years, lemmings become rare. According to the team driven by Norwegian Kyrre L. Kausrud (University of Oslo), with the complicity of French Bernard Cazelles (CRNS-IRD), it is a modification of the quality of snow that throws the winter which could explain this relating disappearance.

The winter, lemmings use the zone of contact between the soil and the layer snows. Ordinarily, a free space forms in the contact of the earth, hotter there, where the lemming can protect itself from cold, and feed. The snow remains piece of furniture, what allows him to dig. But Kausrud and his colleagues show that with winters more warm, the surface of snow melts slightly, before freezing by forming a hard layer who prevents the rodent from going to take refuge under the snow. He suffers from cold, the trouble to feed, and an easier prey for its predators becomes.

From climatic data and information on the populations of lemming and other rodents over twenty-seven last years, researchers constructed a statistical model which reproduces truthfully the variations of population of the lemming. And this model lets think that other animal populations could suffer from the end of the demographic epidemics of the lemming: deprived of this abundant food, the foxes, for example, would turn to other preys. A hypothesis which still asks to be proved, raise two British researchers called to comment on Norwegian jobs in Nature.

(1) Edition of November 6th, 2008

Picture: © Erika Leslie / Nature