The effects of experimental habitat destruction and patch isolation on space use and fitness parameters in female root vole Microtus oeconomus.

The aim of this study was to test whether experimentally induced destruction and fragmentation of habitat and varying degrees of patch isolation applied to 11 experimental populations of root voles affected space use and fitness parameters in radio-tracked females. It was predicted that the habitat destruction would disrupt the spatiosocial relations between breeding individuals, which, in turn, would cause lowered survival and reproductive success. Different degrees of patch isolation were expected to affect the rate of risky and energetically costly interpatch movements. The experimental habitat destruction comprised the removal of more than half of the habitat area (meadow vegetation) in each of seven populations that had been established in a large continous habitat block. This treatment yielded six small, habitat patches arranged in two clusters with long and short interfragment distances, respectively. Measures of individual space use, survival rates (predation and unknown causes) and litter production were contrasted with equivalent measures obtained from four control populations. The control populations had been established in permanently fragmented plots with the same fragment configuration as the post-destruction treatment populations. The effect of different interpatch distance was tested by comparing movement rates, space use and demographic parameters between the two types of patch cluster. Home ranges were larger in the continuous predestruction populations compared to the permanently fragmented control populations. There was a large decrease in home range area of individual females as a result of habitat destruction, and they became temporally smaller than in the control plots. The degree of overlap only increased on home range core areas. The degree of space sharing between matrilineal related females, a main characteristic of Microtus social organization, was higher in the permanently fragmented populations (controls) than in the treatment populations. This difference was also maintained after habitat destruction. Thus, the basic spatio-social organization of reproductive females when first established, seems to be very resistant to habitat destruction. There were no effects of habitat destruction on female fitness parameters when tested for either at the cluster or the population level. There were less between-patch movements when interpatch distances were large than when they were small, irrespective of the fragmentation history of the population. Predation by avian predators, the main mortality cause, was highest in fragment clusters with long interpatch distances, probably because long distance movements between fragments increased the predation risk. There was a large intrapopulation variation with respect to how severely individuals were affected by the habitat destruction. The farther a female had to relocate her home range because of habitat destruction, the higher was the predation risk. Thus, this study predicts that the most influential aspect of habitat fragmentation on demography may be that causing long interpatch movements.