Dynamics of voles and small mustelids in the taiga landscape of northern Fennoscandia in relation to habitat quality

Abstract

In the forests of northern Fennoscandia during the 1980's, the dynamics of microtine rodents changed from multiannual high amplitude fluctuations (cycles) to, depending on species, fluctuations with a strong seasonal component or fluctuations with smaller amplitude and lower frequency Microtine and predator data from the Pallasjarvi area, Finnish Lapland, suggest that this transition took place at different rates in different parts of the taiga landscape Generally, densities m forest habitats have been primarily seasonal since 1985‐86 In mesic spruce taiga and m drier forest habitats microtmes had a prolonged peak in 1981‐83 and a crash in 1984–85 At the timberline, however microtme populations dropped from peak to low densities already in 1982‐83 but the final crash did not occur until spring 1985 The synchronous decrease in microtmes densities m all habitat types in 1984‐85 coincided with increase in weasel activity Activity of other carnivores was consistently high in mesic lowland habitats The data support following three conjectures 1) Periodic abundance of least weasels is crucial for sustained vole cycles 2) Predominance of stoats and other generalist predators lead to less regular fluctuations with a strong seasonal component where density declines occur in autumn and early winter 3) In barren tundra areas, the vegetation cannot sustain high densities of microtmes and, consequently, predation is not a necessary condition for population crashes