A review of ecological interactions of fruit bats in Australian ecosystems

The 13 species of fruit bats in Australia can be separated into five ecological groups: large-sized (>300 g) and small-sized (<60 g) specialist frugivores and nectarivores, and large-sized generalists. Each group contains only one abundant species and one or more rare species. Large nectarivores have a wide distribution which is related to the extent and species diversity of eucalypt forests and woodlands. The frugivorous species have restricted distributions that correspond to the similarly restricted and diminished distribution of rainforest. All identifiable ecological niches available in forest in Australia appear to be filled by at least one frugivorous and nectarivorous species. Specialized frugivores locate food visually, and for one (Pteropus conspicillatus), the dominant dietary components are light-coloured fruits that are prominent against the dark background of the upper canopy of rainforest. The distribution of colony sites of this species is either within or adjoining tropical rainforest. The small tube-nosed bat Nyctimene robinsoni appears to forage only in the sub-canopy zone of rainforest and does not roost in colonies, opting rather to roost by day camouflaged within or near the last food tree used the previous night. Reduced molariform dentition that reflects the absence of mastication of food has evolved in specialized nectarivores such as Pteropus scapulatus and two species of macroglossine bats. Large and highly mobile nectarivores locate food (primarily Eucalyptus blossom) using olfaction, with broad-scale movements over hundreds of kilometres being related to mass flowering. Eucalypt flowering patterns in north Queensland show that droughts can cause reduced nectar production or flowering failure. For P. scapulatus this explains occasional natural mortality coincident with migration to coastal regions. Since flowering failure occurs after 3-4 consecutive months of below-average rainfall, broad-scale migrations of this species can be predicted. The small amount of research that has been conducted to date shows that, although a broad group of pollinators other than bats is available for them, a large suite of Eucalyptus species are dependent upon flying-foxes as their major source of outcrossed pollen. Similarly, the successful regeneration of many rainforest trees is contingent upon seed dispersal by large frugivorous bats; these trees are predominantly those having light-coloured fruits. Successful seed dispersal relates to feeding territoriality; a 'raiders versus residents' concept indicates that the invasion of feeding territories results in the carriage of large propagules away from their parent tree and over long distances. This is especially important in the transmission of genes between different tracts of fragmented rainforest. It is suggested that in the long term the proportion of trees in Australia's tropical rainforest having light-coloured fruits may gradually decline. Ecological mutualism is shown to exist between pteropodid bats and the native forests of Australia.