ABOVE: Rajah maxomys (Maxomys rajah), a common forest rat in Borneo about to feed on a ripe female Ficus cereicarpa fig. In a 3 year (1995-1998) study at Lambir in Sarawak, Rhett Harrison found that female Ficus cereicarpa fig fruits which are produced at the base of the tree trunk, were eaten by rats. Note that other potential dispersers of ground level figs such as Bearded Pigs, Sumatran Rhinos and deer were already locally extinct at Lambir during Harrison’s study. Illustration by Karen Phillipps.
Ficus cereicarpa is dioecious meaning that trees are either male or female. The photo shows a “ripe” male Ficus cereicarpa fig with the pollinating fig wasps about to emerge from the gall flower ovaries (small egg like objects). MaleFicus cereicarpa fig fruits do not produce seeds and usually grow higher up on the trunk (up to about a meter) compared with seed producing figs on female trees which are usually at ground level .A ripe female Ficus cereicarpa fig. The interior is full of a jelly containing thousands of tiny seeds. Each seed on average is 0.8 long x 0.5 mm wide. Ficus cereicarpa seeds are some of the smallest fig seeds in Borneo. In general the species of Bornean figs which produced fig fruits at ground level (earth figs) have the smallest seeds. The most likely reason is that the smaller the seed the greater the chance that it will pass through the gut of an animal or bird unharmed.
In a Sabah study Wells et al (2009) found that although Rajah maxomys rats are known seed predators, they passed seeds up to 1.5 mm wide unharmed in their feces. Thus Rajah maxomys is most likely to be a disperser of Ficus cereicarpa and most other earth figs because their seeds are less than 1.5 mm in width.
Sabah Rat Leopoldamys sabanus the largest lowland forest rat common throughout Borneo. Wells (2000) found that the larger the rat the more likely they were to pass small seeds unharmed. The smaller the rat, the more likely it was to be a seed predator of small seeds. Photo by Jungle Dave at Bidanu, Brunei.Five species of invasive (non native) rats and mice are found in Borneo. Based on a Hawaiian study even invasive species of rats found in farms and gardens in Borneo are likely to be dispersers (not seed predators) of tiny fig seeds. Illustration from Phillipps Field Guide to the Mammals of Borneo (2018)
In a Hawaiian study Shiels (2010) found that three invasive species of rats Rattus rattus,R. exulans and Mus musculus were dispersers of the seeds of Ficus microcarpa which measure 0.9 x 0.7 mm. Only seeds larger than 1.5 mm width are likely to be predated by rats. Thus on the Hawaiian islands invasive rats disperse invasive figs, and the same is probably true in Borneo.
The only rats or mice in Borneo small enough to predate fig seeds are the three species of Sunda Tree mouse (Chiropodomys species) illustrated above and the 2 species of Ranee Mouse Haeromys species, one of which is illustrated below. According to anecdotal reports these 5 species of tree mice are specialist feeders on the seeds of strangling figs. However this hypothesis has yet to be researched. Illustration from Phillipps Field Guide to the Mammals of Borneo (2018)Illustration from Phillipps Field Guide to the Mammals of Borneo (2018)
CONCLUSION: Borneo hosts some 30 species of rat type rodents. The majority of species are likely to be important dispersers of fig seeds. The exception are the 5 species of aboreal tree mice which are believed to predate fig seeds.
