The lemming cycle and the predator-prey interactions: Rodent cycles have been studied for decades and empiricists and theoreticians to explain them have proposed several hypotheses. The predation hypothesis has gained attention during the last 20 years but to date, no study could test it with information collected over several cycles and covering all predator species. The high-Arctic Tundra biome, in NE Greenland, holds the world's simplest terrestrial vertebrate predator-prey community, with only one rodent species (the collared lemming: CL), as the main prey for four predators (snowy owl, long-tailed skua, Arctic fox and stoat). In this region, the CL population is cyclic with a = 4-year long period and a >100-fold amplitude between peak and low phases. The functional and numerical responses of the predators lead to very high predation rates in summer with more than 2% of the CL population being predated per day during the peak and decline phases. These predation rates, much higher (or similar during low phases) than the CL maximum growth rate (˜ 1%), are sufficient to explain why this rodent population systematically faces a decline during summer. During winter, only the stoat actively continues to prey upon the CL under the snow. Contrary to other predator species, the stoat has a delayed numerical response, which contributes to destabilize the system through inversely density-dependent predation rates. The impact of predators and especially the predominant role played by the stoat in causing the cycles was also tested with a parameterized model. The predictions of this model, in line with the empirical observations, support the predation hypothesis for our study area. This model also provides new possibilities to assess the impact of climate change on an entire community or of some specific behavior of the predators like their preferences for some age classes.
Species studied: Collared lemming (Dicrostonyx groenlandicus) and its four main predators in NE Greenland > Long-tailed Skua (Stercorarius longicaudus), Snowy Owl (Nyctea scandiaca), Arctic fox (Alopex lagopus) and Stoat (Mustela erminea) For the four predators: Diet Functional responses to lemming densities Numerical responses to lemming densities
Dept of Ecology and Systematics, Uni. Helsinki (FIN) - Prof. Ilkka HANSKI Institut für Landespflege, Uni. Freiburg (D) - Dr Benoît SITTLER