Monitoring and modelling threats to koala populations in rapidly urbanising landscapes: Koala coast, south east Queensland, Australia

Abstract

The aim of this study was to develop tools for monitoring and modelling threats to wildlife and apply these approaches to koala populations in a rapidly urbanising landscape. The study addressed problems in establishing the conservation status of a population through the examination of the direct and indirect threats to species’ persistence at the landscape scale (10000s ha). Wildlife populations are increasingly under pressure as human activities expand into natural ecosystems. In Australia, rapid population growth along the eastern seaboard is impacting heavily on regional biodiversity and threatening the persistence of many species, including the koala (Phascolarctos cinereus). Land clearing for residential developments and associated infrastructure such as roads, results in direct threats to habitat amount and species abundance; and introduces new threats associated with habitat fragmentation, vehicles, dogs and disease. Effective management of koala populations in these rapidly urbanising landscapes requires detailed regional information and monitoring tools to assess the current conservation status and trends in the population, habitat and threatening processes. This study integrated traditional ecological survey techniques with remote sensing, geographical information systems and landscape fragmentation analysis, to monitor the direct threats of habitat loss; decline in abundance; and contraction in extent of a regional koala population. The associated threats of increased mortality caused by vehicles, dogs and disease were monitored using statistical techniques applied to a long-term data set of incidental koala mortality. Spatial modelling underpinned much of this research and was integrated with satellite image processing for the delineation of potential koala habitat and to assess changes in koala numbers and distribution over time. Spatial modelling was also applied to identify, quantify, map and categorise the major causes of mortality and estimate the impacts on koala persistence. The inter-relationship between landscape configuration, forest fragmentation and the causes of koala mortality were modelled to explain the independent effects of natural and anthropogenic variables. Predictions from these models were tested using geostatistical techniques to determine their suitability for informing threatened species management decision making. The study was conducted in an area of 375km2 known as the Koala Coast, located 20km south-east of Brisbane, South East Queensland, Australia. The study contributes to an understanding of the interrelationship between the koala, the environment, and threatening processes impacting on long-term survival and species’ persistence. The monitoring and modelling tools provide: tools to assess the current condition and changes in conservation status of a koala population based on habitat change; the first regional koala population estimate utilising direct counts; the first assessment of the anthropogenic mortality rate in a regional koala population; the first comprehensive evaluation of road kill blackspots for an entire regional road network (for any wildlife species); and the first enumeration of the association between traffic volume and koala mortality. It is likely that the koala populations on the urban footprint will not be able to withstand the high rates of anthropogenic mortality in addition to natural mortality and that this will result in localised extinctions. Abundance modelling revealed that, if left unchecked, the high mortality and reduction of habitat values will result in the loss of a substantial portion (38%) of the koala population. The landscape configuration of the remaining non-urban area was found to be too small to maintain a minimum viable population of 5000 koalas and indicates that the Koala Coast population may be reaching a point where extinction of the population becomes inevitable. Consequently, immediate management action is urgently needed to implement mortality mitigation measures, improve koala habitat values and prevent any further increases in the size of the urban footprint. Long-term persistence of wildlife in rapidly urbanising landscapes is dependent on the ability to address local threats and implement conservation plans. This study provides some of the tools and approaches to better manage wildlife populations such as the koala. Land managers and planners now need to prevent the loss of koalas and koala populations; mitigate the threats affecting koala survival; reverse the declines in habitat and abundance; and monitor the success of management actions.