Effects of experimental habitat fragmentation and connectivity on root vole demography

1. We used a factorial experimental design to test whether habitat fragment ation (two different fragment sizes) and connectivity (presence and absence of corridors between small fragments) affected population growth rate and two conventional measures of the demographic structure (proportion of repro ductive adults and sex ratio) in 12 enclosed populations of root voles. 2. Because the matriline has been suggested to be a functional entity affec ting the demography of Microtus populations, we employed a study protocol ( including laboratory-raised founder animals and intensive live trapping com bined with fluorescent powder techniques), which enabled us to track the ma trilineal genealogy in the populations. Thus, the effect of habitat structu re on the matrilineal structure of the populations, quantified by the Shann on-Wiener diversity index, could be tested for the first time. 3. Population growth rate was density dependent, but neither this populatio n parameter nor sex ratio and proportion of reproductive adults differed be tween the habitat treatments. This was unexpected since the presumed determ inants of Microtus demography, such as individual space use, dispersal dist ances and spatiosocial organization had earlier been found to differ betwee n the treatments. 4. The matrilineal structure (diversity) of the populations changed in resp onse to the experimental habitat manipulations. In corridor-connected syste ms, some matrilines became numerically dominant, which lead to reduced matr ilineal diversity compared to systems with isolated habitat fragments. We h ypothesize that some matrilines were able to colonize and exploit corridor- connected fragments better than other matrilines. Matrilineal diversity was not related to any other demographic attribute (growth rate, sex ratio and functional stage structure) at the population level. 5. Our results suggest that fragmentation-induced changes of individual and matrilineal level attributes do not necessarily propagate into population level differences in vital rates. The notion that matrilines may be a funct ional entity in Microtus populations could not be supported. 6. Our experimental results suggest that population genetics, more than pop ulation demography, may be sensitive to habitat fragmentation and connectiv ity, within the specific temporal and spatial extent explored. In particula r, the effect of corridors on matrilineal diversity imply that population g enetic studies based on mtDNA markers should consider habitat connectivity when analysing genetic diversity.