Habitat fragmentation in forests affects relatedness and spatial genetic structure of a native rodent, Rattus lutreolus

Habitat fragmentation can have a range of negative demographic and genetic impacts on disturbed populations. Dispersal barriers can be created, reducing gene flow and increasing population differentiation and inbreeding in isolated habitat remnants. Aggregated retention is a form of forestry that retains patches of forests as isolated island or connected edge patches, with the aim of 'lifeboating' species and processes, retaining structural features and improving connectivity. Swamp rats (Rattus lutreolus) are a cover-dependent species that are sensitive to habitat removal. We examined the effects of aggregated retention forestry and forestry roads in native wet Eucalyptus forests on swamp rat gene flow and population genetic structure. We characterized neighbourhood size in unlogged forest to provide a natural state for comparison, and examined population structure at a range of spatial scales, which provided context for our findings. Tests of pairwise relatedness indicated significant differentiation between island and edge populations in aggregated retention sites, and across roads in unlogged sites. Spatial autocorrelation suggested a neighbourhood size of 42-55m and revealed male-biased dispersal. We found no genetic isolation by geographical distance at larger (>2.3km) scales and populations were all significantly differentiated. Our results suggest that removal of mature forest creates barriers for swamp rat dispersal. In particular, roads may have long-term impacts, while harvesting of native forests is likely to create only short-term dispersal barriers at the local scale, depending on the rate of regeneration.