Spatial dynamics in fluctuating vole populations.

Patterns and consistency of distribution, spatial and temporal components, and the extent of spatial density-dependence were compared between semi-cyclic and cyclic populations of the vole species Clethrionomys glareolus and Microtus agrestis in south-central and north Sweden. Cyclic populations were less clumped and only C. glareolus showed a consistency in distribution between years. Spatial variation contributed little to the distributions in cyclic populations while the spatial and temporal variations were of the same magnitude in the semi-cyclic populations. The latter populations could be subdivided into areas with different spatial and temporal components. The spatial density-dependence increased from increase to decline years in C. glareolus but not in M. agrestis, which differed conspicuously between reregions in population development. The data imply that spatial dynamics should be considered as much as temporal ones for non-cyclic populations, that the same regulating or limiting factors may be at work in both spatial and temporal components and that, in addition, social behaviour may be important in explaining spatial dynamics. However, the latter effects may be fairly species-specific.