The relationship between the floristic composition of rain forests and the abundance of folivorous marsupials in north-east Queensland

Abstract

1. Three species of folivorous ringtail possums (Marsupialia: Pseudocheiridae) inhabit higher elevation rain forests on the Atherton Tablelands, north-east Queensland, Australia. Each possum is thought to specialize on a restricted suite of host plants. It has been hypothesized that the absence of the possums from lowland forests may reflect the absence or 'inappropriate combination' of their host plants in lowland forests. 2. We test this 'floristics hypothesis' using data from published dietary studies, herbarium records and field surveys. Studies of the possums' diets show that each possum eats a wide variety of plant species. However, the majority of each possum's diet comes from a few genera or families of plants and there is considerable dietary partitioning between the possums. These data are consistent with the hypothesis that the possums are specialists on a restricted suite of plant taxa. 3. The altitudinal ranges of plants known to be important in the diets of the ringtail possums were compiled from herbarium records. Several plant species eaten by the possums are absent from lowland forests, but all genera and families of plants important in the possums' diets occur in lowland forests. 4. The relationship between the floristic composition of forests and the abundance of the ringtail possums was examined at 16 sites on the Atherton Tablelands. The floristic composition of forests varied primarily with geology and secondarily with altitude. This was true whether the entire plant assemblage was considered, or just those families known to be important in each possum's diet. Possum abundance varied primarily with altitude and secondarily, for two species, with geology. There was no correlation between the abundance of ringtail possums and the floristic composition of forests, whether the entire plant assemblage was considered, or just those families known to be important in each possum's diet. 5. Altitudinal variation in the abundance of ringtail possums in north Queensland does not appear to be a response to variation in the floristic composition of those forests.