Population fluctuations of voles in North Fennoscandian tundra: contrasting dynamics in adjacent areas with different habitat composition

During 1991-1996, we studied population fluctuations of microtine rodents p rimarily Clethrionomys rufocanus), of their winter food plants, and of thei r predators in a low arctic habitat complex, dominated by unproductive lich en dwarf-birch tundra. More productive habitats occurred patchwise througho ut the landscape. On a south-facing slope, productive scrubland habitats pr evailed, and luxuriant habitats were locally abundant. Our main method was live-trapping on 14 grids, representing typical lowland tundra (5 replicate s), the productive slope (4 replicates) and barren high-altitude tundra (5 replicates). Within the slope, vole populations were cyclic. In the lowland tundra, vole fluctuations were primarily seasonal, but the vole crash on t he productive slope coincided with a phase of relatively low vole densities in the lowland. The highland was characterised by low vole densities. Duri ng the phase of rapid population growth, long-range dispersal occurred with in the slope and from the slope to surrounding areas. Moreover, small muste lids which had initially been present only on the slope, started to move el sewhere, along natural dispersal corridors. Shoot mortalities of the main w inter food plant, Vaccinium myrtillus, remained low. The observed scenario is consistent with the hypothesis that vole cycles represent a mustelid-mic rotine limit cycle, because cycles created by this mechanism should disappe ar when the productive habitats, capable of supporting resident predators, become fragmented and embedded in a vast unsuitable area.