Tree use by koalas in a chemically complex landscape
Ben D. Moore1† & William J. Foley1
1School of Botany and Zoology, Australian National University, Canberra ACT 0200, Australia
†Present address: School of Tropical Biology, James Cook University, Townsville QLD 4811, Australia
Although defence against herbivores is often argued to be the main action of plant secondary metabolites (PSMs)1, very few examples have demonstrated that intraspeciﬁc variation in PSM concentrations inﬂuences foraging by wild vertebrate herbivores 2,3. Experiments with captive animals often indicate that PSM concentrations inﬂuence how much herbivores eat from individual plants3–7, but these experiments do not replicate the subtle trade offs in diet selection faced by wild animals, which must avoid predators and extremes of weather, interact with conspeciﬁcs, and achieve a balanced, nutritious diet, while avoiding intoxication by PSMs. We characterized the foliar chemistry of every tree from two Eucalyptus species available to a population of koalas (Phascolarctos cinereus) and considered rates of tree visitation over a ten-year period. We show that visitation rate was most strongly inﬂuenced by tree size, but that koalas also visited trees less frequently if the foliage contained either high concentrations of deterrent PSMs known as formylated phloroglucinol compounds, or low concentrations of nitrogen. Consequently, plant chemistry restricts the use of treesby this herbivore,and thus limits the food available to koalas and potentially inﬂuences koala populations.