A mother and baby Sumatran Rhinoceros eating fallen wild mango fruits in Borneo, whilst a pair of Bulwer’s Pheasants search for grubs in an old rhino dung pile. (Illustration by Karen Phillipps)
Sumatran Rhinos are now almost extinct in Borneo, but there is no doubt at all, that both Sumatran and Javan Rhinos were once extremely common in the forests of Borneo. Hunting rhinos for their horns (used in traditional Chinese medicine) has led to a population collapse.
Feeding experiments on the captive rhinos at BORA (Borneo Rhino Alliance) at Tabin in Sabah show that the rhinos are fond of all types of forest fruit and eat a very large variety of leaves and twigs of secondary forest shrubs and sapling trees, especially figs.
The most likely explanation of how Ficus aurata was dispersed in the past is that whenever you see a Ficus aurata fig plant you are standing next to the location of an ancient rhino dung pile. Despite it’s apparent abundance today Ficus aurata is an anachronistic fruit doomed to follow the rhino to eventual extinction in Borneo.
The seeds of most secondary forest shrubs only germinate when exposed to full sunlight so they may lie in the forest soil for many years (soil bank) waiting for a lighting up event such as a landslide or falling tree to open the canopy above. These days in Borneo the lighting up event is normally road construction. New roads in Borneo are rapidly lined with an abundance of the pioneer plants (including many figs) favoured by elephants and rhinos.
The current levels of forest disturbance in Borneo (resulting from human activities) are unprecedented over the past few million years and the dominance of pioneer plants such as Ficus aurata over large areas is also unprecedented. In most of Borneo the original dispersers of these plants (elephants and rhinos) have become extinct- so we are seeing a one off event never to be repeated.
See this interesting article on the Foliage is Fruit Hypothesiswritten by the ecologist Daniel Janzen in 1984.