SPACE-USE RESPONSES TO HABITAT FRAGMENTATION AND CONNECTIVITY IN THE ROOT VOLEMICROTUS OECONOMUS

Abstract

We radiotracked 184 reproductive active root vole Microtus oeconomus individuals in 12 experimentally fragmented populations to test predictions regarding responses in spatiosocial organization to habitat fragmentation and connectivity. We used two genetically distinct strains with different intrinsic characteristics to test explicitly for interactions between spacing behavior and the degree of habitat fragmentation and connectivity. The experimental habitat configurations were created by mowing enclosed meadow plots so that habitat (meadow) fragments were imbedded in a hostile, barren matrix of nonhabitat. We used three types of habitat patch configurations to contrast two levels of fragmentation (large vs. small habitat fragments) and two levels of connectivity (small isolated vs. small corridor connected habitat fragments), while keeping the total area of habitat and distances between fragments constant. The least fragmented systems contained two habitat fragments large enough to encompass several female home ranges (large fragment plots). Both of the two other habitat configurations contained six small habitat fragments, each of the size corresponding to the home range of a single female. The two small fragment configurations differed with respect to connectivity in that one configuration had 0.5 m wide corridors connecting two triplets of patches (corridor plots), while the other small patch configuration had no corridors (small fragment plots). Four population replicates (two of each root vole strain) of each configuration were employed over two years. Home range area estimates showed rather complex responses to habitat fragmentation depending on strain and sex. This was expected as the two strains and males and females had been previously shown to exhibit different space requirements. Core areas were, however, unaffected by fragmentation pattern at the spatial scale employed. The most pronounced and consistent responses to habitat fragmentation concerned movement rates for both sexes and the degree of space sharing between matrilineally related and unrelated females. The frequency of home range overlaps (irrespective of matrilineal relatedness and strain) was highest in the large-fragment plots and lowest in the small-fragment plots. The degree of overlap between matrilineally related females showed a reverse trend, however, indicating that space sharing was more directed towards kin in the most fragmented systems. The rate of interfragment movements increased with habitat fragmentation. Corridors induced more individuals to move between the smallest fragments. Males generally moved more frequently between fragments than did females. Our results match the hypothesis predicting fusion and fission responses based on intrinsic social mechanisms in patchy populations.