DENSITIES OF MICROTINE RODENTS ALONG A POLLUTION GRADIENT FROM A COPPER-NICKEL SMELTER

Population densities of microtine rodents were studied along an air po llution gradient in the Kola Peninsula, Russia, by long-term and short -term trapping. The study area is affected by high sulphur dioxide and heavy metal emissions from the Severonikel copper-nickel smelter in M onchegorsk. The density of Clethrionomys rufocanus, the most abundant vole species in the area, was lowest close to the smelter and increase d with distance up to the farthest, less polluted trapping sites. Clet hrionomys glareolus, C. rutilus and Lemmus lemmus were absent from the most severely damaged area and were also scarce at the moderately pol luted area 28 km south of the smelter. Although the population of C. g lareolus has previously been cyclic at the moderately polluted area, w e were unable to demonstrate any regular cycle. The most likely explan ation for the low number of microtine rodents in the damaged and moder ately polluted areas is a decrease in the quantity of important food p lants: epiphytic lichens for C. glareolus and possibly C. rutilus, mos ses for L. lemmus and seed plants, especially Vaccinium myrtillus, for C. rufocanus. Close to the smelter, direct toxic effects of heavy met als may also reduce population densities. The results show that pollut ants may change the relative proportions of microtine species.