Changes in possum spatial ecology following density reduction: implications for conservation and bovine tuberculosis management

Although a number of animals have been recorded changing their spatial distribution following density reduction, the mechanisms of this spatial perturbation are not always clear and may vary among species. Experimentally investigating how spatial perturbations affect space use increases our understanding of the spatial organisation of populations and allows the better management of pest species. For example, understanding changes in movement patterns may allow the determination of optimal control strategies, such as the timing and duration of control. The possum in New Zealand is a pest, affecting our native flora and fauna, and transmitting bovine tuberculosis to livestock. Possums exhibit a dominance hierarchy, with dominant individuals preventing subordinates accessing limited resources and likely regulating their space use. Therefore, we hypothesised that population reduction would result in survivors changing their space use, due to less aggression and competition. To test this, we monitored the spatial ecology of three possum populations; two subjected to density reduction and an experimental control site not subjected to density reduction. Possum movements were monitored using VHF and GPS collars to determine changes in den-site, home-range and pasture use. We identified changes in a number of movement parameters due to density reduction. For example, average home-range sizes increased at the two treatment sites by 106% and 93% following density reduction. This research further highlights the need for efficient control that reduces possum populations to very low densities, due to increases in possum space use and consequently potential increases in bovine tuberculosis transmission risk