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

摘要

During 1991-1996, we studied population fluctuations of microtine rodents (primarily Clethrionomys rufocanus), of their winter food plants, and of their predators in a low arctic habitat complex, dominated by unproductive lichen dwarf-birch tundra. More productive habitats occurred patchwise throughout the landscape. On a south-facing slope, productive scrubland habitats prevailed, and luxuriant habitats were locally abundant. Our main method was live-trapping on 14 grids, representing typical lowland tundra (5 replicates), 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 the productive slope coincided with a phase of relatively low vole densities in the lowland. The highland was characterised by low vole densities. During the phase of rapid population growth, long-range dispersal occurred within the slope and from the slope to surrounding areas. Moreover, small mustelids which had initially been present only on the slope, started to move elsewhere, along natural dispersal corridors. Shoot mortalities of the main winter food plant, Vaccinium myrtillus, remained low. The observed scenario is consistent with the hypothesis that vole cycles represent a mustelid-microtine limit cycle, because cycles created by this mechanism should disappear when the productive habitats, capable of supporting resident predators, become fragmented and embedded in a vast unsuitable area.