Which trees do wild common brushtail possums (Trichosurus vulpecula) prefer? Problems and solutions in scaling laboratory findings to diet selection in the field

In this study, we examined whether a group of plant secondary metabolites - the formylated phloroglucinol compounds (FPCs), which are known to deter feeding on eucalypt foliage by captive marsupial folivores - influence feeding by wild common brushtail possums. There was at least a six-fold range of FPC concentrations in the foliage of individual trees within a single eucalypt species. Possums largely avoided trees with high FPC concentrations. While some trees with low FPCs were used heavily, others were not; thus the relationship between FPC concentration and tree use was polygonal rather than linear. We used a randomization procedure to demonstrate a relationship between the upper limits of FPC concentration and tree use. In contrast, this procedure showed that neither the nitrogen content nor the in vitro digestibility of the leaves influenced the use of trees by possums. Our results show that plant secondary metabolites, with a demonstrable mode of action, affect the selection of individual eucalypt trees by wild folivores. Thus, FPC concentrations may influence the distribution and abundance of marsupial folivores at landscape scales.