Using integrated population modelling to quantify the implications of multiple threatening processes for a rapidly declining population

Jonathan R. Rhodesa,b,*, Chooi Fei Nga,b, Deidré L. de Villiersc, Harriet J. Preecec, Clive A. McAlpinea,b, Hugh P. Possinghamb

aThe University of Queensland, Centre for Spatial Environmental Research, School of Geography, Planning and Environmental Management, Brisbane, QLD 4072, Australia
bThe University of Queensland, The Ecology Centre, Brisbane, QLD 4072, Australia
cQueensland Department of Environment and Resource Management, P. O. Box 15155, City East, QLD 4002, Australia

Many species of conservation concern are in decline due to threats from multiple sources. To quantify the conservation requirements of these species we need robust estimates of the impact of each threat on the rate of population decline. However, for the vast majority of species this information is lacking. Here we demonstrate the application of integrated population modelling as a means of deriving robust estimates of the impact of multiple threats for a rapidly declining koala (Phascolarctos cinereus) population in Southeast Queensland, Australia. Integrated population modelling provides a basis for reducing uncertainty and bias by formally integrating information from multiple data sources into a single model. We quantify mortality rates due to threats from dog attacks, vehicle collisions and disease and the extent to which each of these mortality rates would need to be reduced, or how much habitat would need to be restored, to stop the population declining. We show that the integrated population modelling approach substantially reduces uncertainty. We also show that recovery actions that only address single threats would need to reduce those threats to implausibly low levels to recover the population. This indicates that strategies for simultaneously tackling multiple threats are necessary; a situation that is likely to be true for many of the world’s threatened species. This study provides an important framework for quantifying the conservation requirements of species undergoing declines due to multiple threats.