Climate change stifling lemmings

Packs of Norway lemmings aren’t necessarily headed off a cliff, but climate change in a part of that country certainly seems to have stifled population spikes of the oft-prolific creature in recent decades.

Lemmings are famed for their population booms: Occasionally, across small regions, their numbers can briefly swell a hundredfold. Dramatic increases of the rodents typically occur every three to five years, says Nils Christian Stenseth, an evolutionary ecologist at the University of Oslo in Norway.

But at one site in south-central Norway, lemming populations haven’t spiked in such a way since 1994, he notes. In the Nov. 6 Nature, Stenseth and his colleagues suggest that climate change has interrupted the normal boom-and-bust cycle of lemming populations.

Norway lemmings, Lemmus lemmus, are about half the size of a guinea pig and live in nests beneath the snow during the winter months. When the snowpack is light and fluffy, warmth from the ground melts small spaces under the snow that the lemmings use to forage for sedges, grasses and mosses without being exposed to predators. But in recent years, warmer winter temperatures have rendered the snow less fluffy. That, in turn, has made the snow more likely to melt and refreeze at ground level, coating the ground with ice and making life more difficult for lemmings.

Climate change is affecting the entire ecosystem of the region that Stenseth and his colleagues studied, the researchers contend. With the recent lack of population booms among lemmings, predators such as arctic foxes and snowy owls have turned their attention to other prey, including ground-nesting birds such as ptarmigan and grouse, whose numbers have declined.
“When you significantly affect the numbers of one species like this, it’s bound to have consequences,” says Tim Coulson, an ecologist at Imperial College London in Ascot, England. Although the recent change in lemming population cycles largely has no apparent effect on humans, “it’s a warning sign of effects that global warming could have on other species,” he notes.

Because scientists understand remarkably little about many species interactions within an ecosystem, the new findings illustrate the importance of long-term studies of animal and plant populations, he adds.