Linking climate change to lemming cycles

The population cycles of rodents at northern latitudes have puzzled people for centuries1,2 , and their impact is manifest throughout the alpine ecosystem2,3 . Climate change is known to be able to drive animal population dynamics between stable and cyclic phases 4,5 , and has been suggested to cause the recent changesin cyclic dynamics of rodents and their predators 3,6–9 . But although predator–rodent interactions are commonly argued to be the cause of the Fennoscandian rodent cycles 1,10–13 , the role of the environment in the modulation of such dynamics is often poorly understood in natural systems 8,9,14 . Hence, quantitative links between climatedriven processes and rodent dynamics have so far been lacking. Here we show that winter weather and snow conditions, together with density dependence in the net population growth rate, account for the observed population dynamics of the rodent community dominated by lemmings (Lemmus lemmus) in an alpine Norwegian core habitat between 1970 and 1997, and predictthe observed absence of rodent peak years after 1994. These local rodent dynamics are coherentwith alpine bird dynamics both locally and over all ofsouthern Norway, consistent with the influence of large-scale fluctuations in winter conditions. The relationship between commonly available meteorological data and snow conditions indicates that changes in temperature and humidity, and thus conditions in the subnivean space, seem to markedly affect the dynamics of alpine rodents and their linked groups. The pattern of less regular rodent peaks, and corresponding changes in the overall dynamics of the alpine ecosystem, thusseemslikely to prevail over a growing area under projected climate change.