A relative shortage of nitrogenous food in the ecology of the koala (Phascolarctos cinereus)

The disparity between the distribution and abundance of the koala (Phascolarctos cinereus) and its major food trees (Eucalyptus spp.) is examined in terms of the essential oil content of the leaves, the influence of weather, social behaviour, and the level of available nitrogenous food. The essential oils are considered to be relatively unimportant since the koala has the ability to detoxify them. It is proposed that the level of available nitrogenous food is the major limiting influence on the abundance of the koala. Social behaviour enables a few koalas to acquire sufficient food while the majority of the population is subject to a relative shortage of food. The weather varies the local availability of adequate nitrogenous food by its influence on leaf growth in the eucalypts. Unusually favourable weather or inappropriate management which lead to a local increase in the availability of young growing leaves (flush growth) may result in outbreaks in koala numbers.