Predator-prey relationships: Arctic foxes and lemmings

1. The number of breeding dens and litter sizes of arctic foxes Alopex lago pus were recorded and the diet of the foxes was analysed during a ship-base d expedition to 17 sites along the Siberian north coast. At the same time t he cyclic dynamics of coexisting lemming species were examined. 2. The diet of arctic foxes was dominated by the Siberian lemming Lemmus si biricus (on one site the Norwegian lemming L. lemmus), followed by the coll ared lemming Dicrostonyx torquatus. 3. The examined Lemmus sibiricus populations were in different phases of th e lemming cycle as determined by age profiles and population densities. 4. The numerical response of arctic foxes to varying densities of Lemmus ha d a time lag of 1 year, producing a pattern of limit cycles in lemming-arct ic fox interactions, Arctic fox litter sizes showed no time lag, but a line ar relation to Lemmus densities. We found no evidence for a numerical respo nse to population density changes in. Dicrostonyx. 5. The functional or dietary response of arctic foxes followed a type II cu rve for Lemmus, but a type III response curve for Dicrostonyx. 6. Arctic foxes act as resident specialist for Lemmus and may increase the amplitude and period of their population cycles. For Dicrostonyx, on the ot her hand, arctic foxes act as generalists which suggests a capacity to damp en oscillations.