The recovery of populations of bush rat Rattus fuscipes in forest fragments following major population reduction.
Abstract
Understanding the recovery of populations after disturbance is critical to many aspects of applied population management, ranging from the development of conservation strategies to pest control. We used a controlled and replicated field experiment conducted in Tumut, New South Wales, Australia, linked to a genetic study to examine the rate and mechanism of population recovery of the Australian bush rat (Rattus fuscipes) after severe experimental population reduction. The main factors examined were perturbation treatment (removal of animals, removal followed by restocking, no removal), patch size and patch isolation. Although large numbers of animals were removed from many patches, on average populations recovered to pretreatment levels within 2 years. Populations rebounded to levels that appeared to approximate patch carrying capacity. Initially, small populations recovered to a small size and those that were large were also large 24 months later. No significant relationships between population recovery and patch size and isolation were identified. There was an effect of initial population size on proportional trapping success: a higher proportion of initially large populations was trapped than smaller ones. Genetic analyses revealed a significant genetic change following experimental perturbation. Rapid population recovery was mostly via residual animals (and their offspring) that escaped capture, rather than colonization from neighbouring populations. This study has implications for vegetation and habitat management in fragmented landscapes where disturbances such as fire occur. Parts of a habitat fragment that escape disturbance, or are partially disturbed, may continue to support suitable habitat and be a source of animals, thereby facilitating population recovery. Post-disturbance human activities (e.g. salvage harvesting of fire-damaged trees) can modify refugial habitats and, in turn, impair population recovery and species persistence in fragmented landscapes. These activities require careful management to ensure biota are not negatively impacted.