Will future climate change threaten a range restricted endemic species, the quokka ( Setonix brachyurus), in south west Australia?

Abstract

Range-restricted species, such as regional endemics, possess traits that may make them particularly vulnerable to environmental change. The quokka, Setonix brachyurus, is a small macropod, endemic to south-western Australia and two adjacent islands. Climatic factors appear to play a role in defining the distribution of this species. Mainland populations are historically restricted to areas with an annual average rainfall in excess of 700 mm and their current distribution is almost completely confined within the 1000 mm rainfall isohyet. As such, the predicted increasing aridity of south-western Australia due to climate change is likely to threaten the continued persistence of the quokka on the mainland. To examine this possibility, we modelled the distribution of the quokka with Maxent using records of occurrence and a combination of historical climate (1961–1990) and habitat variables. Future projections of this distribution were then examined assuming two simple dispersal scenarios (zero and full migration) and three climate-change scenarios of increasing severity for 2030, 2050 and 2070. The predictive performance of the distribution model generated under historical climate conditions was high (AUC > 0.8), with annual precipitation contributing the most information to the model. Except for the low-severity climate-change scenario under the full dispersal assumption, the future projected distribution of quokka was shown to contract over time. The extent of range contraction tended to increase with the severity of the climate-change scenario, with the species predicted to lose almost all range by the year 2070 under the most extreme climate-change scenario. The results indicate the importance of identifying potential refuges for the quokka (i.e. areas where the species is predicted to persist) and defining management strategies to protect these areas from threatening processes.