Predator–prey relationships: arctic foxes and lemmings

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Abstract
1. The number of breeding dens and litter sizes of arctic foxesAlopex lagopuswere recorded and the diet of the foxes was analysed during a ship‐based expedition to 17 sites along the Siberian north coast. At the same time the cyclic dynamics of co‐existing lemming species were examined.2.The diet of arctic foxes was dominated by the Siberian lemmingLemmus sibiricus(on one site the Norwegian lemmingL. lemmus), followed by the collared lemmingDicrostonyx torquatus.3.The examinedLemmus sibiricuspopulations were in different phases of the lemming cycle as determined by age profiles and population densities.4.The numerical response of arctic foxes to varying densities ofLemmushad a time lag of 1 year, producing a pattern of limit cycles in lemming–arctic fox interactions. Arctic fox litter sizes showed no time lag, but a linear relation toLemmusdensities. We found no evidence for a numerical response to population density changes inDicrostonyx.5.The functional or dietary response of arctic foxes followed a type II curve forLemmus, but a type III response curve forDicrostonyx.6.Arctic foxes act as resident specialist forLemmusand may increase the amplitude and period of their population cycles. ForDicrostonyx, on the other hand, arctic foxes act as generalists which suggests a capacity to dampen oscillations.