Responses of two species of heathland rodents to habitat manipulation: Vegetation density thresholds and the habitat accommodation model

The abundance of two native rodent species, Rattus lutreolus and Pseudomys gracilicaudatus, has been shown to correlate with vegetation density in coastal wet heath. Fox's habitat accommodation model relates relative abundances of such small mammal species to heathland vegetation regeneration following disturbance. Implicit in the model is recognition that it is successional changes in vegetation, not time per se, that drives the responses of small mammal species along a regeneration axis. Using a brush-cutter we deliberately removed approximately 85% of vegetation around trapping stations and recorded significant reductions in the abundance of both P. gracilicaudatus (an earlier-stage colonizing species) and R. lutreolus (a late seral-stage species). A significant decrease in the abundance of only the latter had been demonstrated previously when 60-70% of the vegetation had been removed. Following the brush-cutting both species re-entered the mammalian secondary succession at different times, first P. gracilicaudatus followed by R. lutreolus after the vegetation cover thresholds of each species had been reached. The impact of this habitat manipulation experiment was to produce a retrogression of the small mammal succession, experimentally demonstrating causality between changes in vegetation density and subsequent small mammal habitat use.