MODELING SURVIVAL RATES - HABITAT FRAGMENTATION AND DESTRUCTION IN ROOT VOLE EXPERIMENTAL POPULATIONS

The effects of habitat destruction and fragmentation on survival rate and population size were tested in an experimental model system consis ting of seven enclosed populations of root voles, Microtus oeconomus. The study comprised two consecutive parts. First, the effect of habita t fragmentation was investigated by comparing survival in three popula tions inhabiting continuous habitat with that in four populations inha biting fragmented habitat. Second, the continuous habitats were experi mentally fragmented by destroying 50% of the area inhabited by the pop ulations, producing the same configuration as in the fragmented habita ts. These extensive habitat manipulations were expected to affect surv ival rates due to changes in the spatiosocial structuring of the popul ations. Throughout the study, populations were monitored by an intensi ve live-trapping program. Cormack-Jolly-Seber methodology was used for statistical modelling and estimation of survival rates. The seven exp erimental populations differed considerably in population dynamics: so me grew, while others remained remarkably stable throughout the experi ment. In contrast to expectations, neither population size nor surviva l rates seemed to be affected by the experimental treatments. Survival rate seemed to play a minor role in determining population size. Emig ration rates, which also seemed to have little direct demographic impo rtance, were considerably higher in fragmented than in continuous habi tats during the first (pre-destruction) part of the study. Surprisingl y, this difference persisted after habitat destruction, when all popul ations experienced the same habitat configuration. We conclude that su rvival rates in these root vole populations were not dependent on majo r alterations of spatiosocial structure, possibly owing to adaptation to natural disturbance regimes.