Interspecific Competition between Small Rodents in Subarctic and Boreal Ecosystems

Cyclic small rodent populations have been studied in northern Fennoscandiafor many years. In this paper interspecific competition is reviewed with Microtus agrestis in focus. Studies have been made in three biogeographical zones with different species composition. Generally larger and stronger species dominate smaller ones. However, the habitat range of a dominant species is usually narrower than that of an inferior one, which enables the survival of the latter one. Violent cyclic changes in densities highly influence the degree of competition; in addition the peaks vary in magnitude. The population performance of M. agrestis depends on its situation in a species hierarchy and on the landscape structure. Microtus oeconomus and Lemjnus lemmus are completely or partly superior to M. agrestis. Clethrionomys-species (C. rufocanus, C. glareolus and C. rutilus) are slightly or considerably inferior to M. agrestis.