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.
These are the tiny seeds of Ficus aurata. They are approximately 1 mm long and 0.75mm wide. Botanists call the seed at the lower left the “fruit” as it is still surrounded by the original flower parts (stigma, style, ovary and tepals) of the original tiny flower. You will note that the tepals are sharp fiberglass like hairs.A ripe fig of Ficus aurata. Note the abundant sharp white hairs surrounding the seeds and the absence of any juicy edible pulp. The purpose of fruit pulp is to encourage a potential disperser to swallow the fig whole and disperse all the seeds. There are over 100 seeds in this fig.A fresh ripe Ficus aurata fig full of seeds. Note that the fig itself is covered in rough hairs. Why would any disperser, bat or bird want to swallow the fig and disperse the seeds and why the need to protect the seeds with so many sharp hairs ? (Photo Arlene Walshe)The most likely explanation for the abundant internal and external sharp hairs of Ficus aurata figs is to preventthe figs from being eaten and the seeds from being predated by Treron green pigeons. (Photo Arlene Walshe)There are five species of Treron green pigeons in Borneo. All of them have tough elastic gizzards which they fill with grit so that they can grind up small seeds. All five species are fig seed predators and 4 species feed almost exclusively on figs. (Illustration by Karen Phillipps)The Pink-necked Green Pigeon Treron vernans is an abundant green pigeon in the secondary forest habitats preferred by Ficus aurata.Although green pigeons are fig eating specialists they do not eat the figs of Ficus aurata. No bird or bat is known to swallow Ficus aurata figs whole and disperse the seeds.Ficus aurata is a very common fig in recently opened up secondary forest throughout lowland Borneo, here growing as a large shrub in the Crocker Range, Sabah near the Kipandi butterfly farm. But how was the original seed from which this fig plant grew originally dispersed ? And how did it end up at this very spot ?Fruiting Ficus aurata stems are one of the most favoured food plants eaten by the captive Sumatran Rhinos at the BORA compound at Tabin.
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.
