Latitudinal Gradients in Predator-Prey Interactions, Cyclicity and Synchronism in Voles and Small Game Populations in Finland

Finnish game questionnaire data from 1964-83 have been used to study cyclicity and the synchronism between species in population fluctuations of voles and 10 small game species. All the species are cyclic in at least some provinces. The most clearly cyclic species are black grouse and hazel grouse, with 6-7 yr cycles. Stoat, weasel and voles are representatives of the 3-4 yr type. The observed cycle lengths are concentrated in years four and seven. The degree of cyclicity is much higher in northern Finland than in southern provinces. The fluctuations of predators and their prey are not simultaneous. However, there is synchronism between ecologically similar species or synchronism (with time lag) between a predator and its prey. The relatively weak synchronism of voles to other species, the disharmony in the distribution of cycle lengths and the contradictory predator-prey relationships suggest that the alternative prey hypothesis cannot explain the origin of, for instance, tetraonid cycles.