Robert Clark (University of Wollongong)
Modelling the Relationship between Leaf Chemistry and Koala Population Density
The koala’s continued survival in many parts of Australia is uncertain. Such is the concern over the declines in koala populations in recent years that the Australian Government set up a Senate inquiry to investigate the issue and possible solutions. That inquiry ran for most of 2011 and released a report in September titled ‘The koala—saving our national icon’. While the report proposes a number of actions to address the problem of declining koala numbers, a fundamental question remains regarding the distribution of koalas across eastern Australia. This presentation will describe the design and preliminary analysis of a study relating habitat characteristics, particularly leaf chemistry, to koala population density. The outcome variable, population density, was actually known prior to sampling areas, based on historical observation by ecologists. Explanatory variables, including tree species and chemical composition of leaves, were then collected by taking transect samples of trees, and intensively analysing leaf samples in the lab. Preliminary results are that tree subgenera is the most powerful predictor, probably mediated by the available nitrogen content of leaves. The analysis is complicated by the presence of spatial effects, zero densities, large extreme values, and loss of power due to aggregation to area level.