Overabundance in Koalas: A Multidisciplinary Approach

Submission note: A thesis submitted in total fulfilment of the requirements for the degree of Doctor of Philosophy to the Department of Ecology, Environment and Evolution, School of Life Sciences, College of Science, Health and Engineering, La Trobe University, Victoria, Australia.

The impacts of overabundance in animal populations often have social as well as ecological dimensions. Managing this issue therefore requires social and ecological approaches thinking beyond disciplinary boundaries is required to improve conservation outcomes. Empirical evidence of both dimensions is needed to support evidence-based decision making. This thesis takes a multi-disciplinary approach to generate evidence to support the management of overabundant koalas (Phascolarctos cinereus). Over browsing by overabundant koalas can lead to severe tree dieback and ultimately to the starvation of koalas themselves. The dominance of manna gum (Eucalyptus viminalis) appears to play a role in the occurrence of koala overabundance, yet the mechanism behind overabundance is still unclear. A possible answer lies in leaf chemistry, as it is known to influence tree use and feeding preferences of koalas. Several management responses have been adopted to manage koala overabundance and its impacts, with translocations and fertility control being the most popular methods. Widespread culling is regularly used in managing other charismatic Australian species and has been advised by experts for the management of overabundant koalas. However, it is currently not used to manage koalas, anecdotally due to public aversion to culling koalas. However, empirical evidence on public opinion is currently lacking to support this approach. This thesis aimed to determine whether stand level differences in leaf chemistry of manna gums can explain why some sites have developed overabundant populations while others did not, quantify online sentiments towards koala culling, and conduct a nationwide survey to assess both the public’s and expert’s acceptability of different management options and how underlying values and beliefs about human wildlife relationships shape social acceptability of different koala management options. Firstly, manna gum leaves and soil samples were collected from seven overabundant sites and seven control sites around Victoria in order to compare stand level differences in leaf chemistry. Comparing the nutritional quality and defensive chemistry of leaves between these sites did however not reveal any significant differences. Leaf chemistry therefore did not appear to be a key driver of overabundance in koala populations at a landscape scale. Sites of overabundance were on average located in closer proximity to the coast. Understanding what factors are and are not involved in koala overabundance will help advance research aimed at understanding and predicting where overabundance might occur media texts was explored and tested to analyse people’s online opinions in comments on news stories on culling koalas kangaroos and feral horses (brumbies). The polarity of sentiments in comments on culling these species was tested as well as whether sentiment was related to support for culling and whether specific sentiment words related to comments on the culling of specific species. While sentiment in comments did not differ between species, there was variation in commenters support for culling. Support for culling kangaroos could be predicted from the sentiment scores but not support for culling koalas or feral horses. The combination of Sentiment Analysis with indicator analysis proved to be useful at identifying key words for determining the topics driving sentiment patterns. Sentiment Analysis can be a valuable analytical tool in exploring online opinions but as the lack of correlation between sentiment and support for koalas and feral horses show further investigation and development of methods are warranted. Thirdly, a nationwide survey was undertaken to obtain empirical data on both the general publics and experts’ opinions on how to best manage overabundant koalas. Two other charismatic but locally overabundant species, kangaroos and feral horses were included in the general public’s survey to explore whether people responded different to koalas than to other species. The results showed that the general public had different levels of acceptability for different species and for different control methods. This was particularly the case for lethal control methods which were generally found to be less acceptable or unacceptable. In contrast, experts found most koala control methods acceptable revealing a substantial mismatch in opinions with the general public that could lead to conflict in koala management. Providing information on the impacts of overabundance increased the publics acceptability of some methods although the effect sizes were small. Having animalistic values and dominionistic beliefs were found to be most useful cognitive factors in explaining the acceptability of management options, increasing our understanding of what is at the base of people’s opinions. This thesis has taken a multidisciplinary approach to explore both ecological and human dimensions of the management of overabundant koalas and investigate gaps in the evidence used in management. The integration of the findings into decision making will be a next step in improving conservation outcomes.