Christmas Island and the Cocos Keeling islands are two very remote  small islands  in the Indian Ocean under the jurisdiction of the Australian Government.  The nearest large land mass is the island of Java which is approximately 350 km from Christmas Island. The nearest landmass to the Cocos Keeling islands is Sumatra c. 900 km distant.

GOOGLE MAP Christmas Island and Cocos Keeling Islands 

Christmas Island hosts two species of figs Ficus microcarpa and Ficus saxophila  both of which are abundant on the island  and 10 species of endemic mammals and birds including an endemic Flying Fox fruit bat and an Imperial Pigeon.   Cocos Keeling has no figs and no endemic birds or mammals. What can these two isolated islands tell us about  fig dispersal and ecology ?

02 Ficus saxophila  Java Atlas  - Copy.jpg
Ficus saxophila is a common fig (Section Urostigma) of the seasonally dry coastal areas  of Vietnam and Thailand to the Philippines, Java, Sulawesi and the Lesser Sunda Islands. The  distribution appears to be relict as there are no records from the the Malay Peninsula, apart from Pulau Langkawi. This fig is also absent from the “wet rainforest ” islands of Borneo and Sumatra where presumably it has become extinct. Illustration from the the Atlas der Baumarten von Java
03 F. microcarpa - .jpg
Ficus microcarpa  is one of the most common figs of   small islands,  coastal swamp forest and  rocky coasts from Sri Lanka north to  southern Japan, south to Australia and east to New Guinea.
Christmas Island Map.jpg
Christmas island  has an area of 13,500 ha, the  majority of which is still covered in rainforest. Since it was settled by humans c. 1850,  4 endemic mammals including two rats, a shrew and an insectivorous bat have become extinct.
02 Christmas-Island-Fruit-Bat .jpg
The Christmas Island Flying Fox is the only endemic mammal remaining on Christmas Island where it is locally common and an important disperser of the 2 species of fig trees. Flying Foxes are the most important dispersers of island fruit seeds  throughout S E Asia and the Pacific.
02 Carpophaga whartoni Keulemans .jpg
The Christmas Island Imperial Pigeon  is one of 7 species of endemic birds found on Christmas Island. Imperial Pigeons are important dispersers of figs and nutmegs from one small island to another throughout S E Asia  and the Pacific. However there are no nutmegs (Myristicacea)  on Christmas Island.

In summary there are a number of land bird and bat dispersed  plants native to Christmas Island including Pipturis argenteus and  Cinnamomum iners  as well as the 2 figs which could only have arrived  in the gut of a bird or bat. However there are no land-bird or bat dispersed plants on the Cocos Keeling Islands. 

The native plants of the Cocos Keeling islands are either sea or sea bird dispersed. The most common native tree on the Cocos Keeling Islands is Pisonia grandis which is dispersed by  seabirds  particularly Frigatebirds.

CONCLUSION Most of the small islands of SE Asia  host both Imperial Pigeons and Flying Fox fruit bats  of many different species. These animals are capable of dispersing  figs very long distances between islands. In the case of Christmas Island  and Cocos Keeling islands at least 350 km but less than 900 km.

The question then arises – if the sea gap between  Borneo and Sulawesi is less than 150 km why are not more Bornean figs found in Sulawesi and more figs from Sulawesi not found in Borneo ?

02 Wallaces Line - Copy.jpg

It is commonly assumed that because figs originated in NE India that  fig migration was exclusively  West to East  from Borneo to Sulawesi across Wallace’s Line and onto the Pacific Islands and Australia.  In fact there are quite a number of figs which  after having crossed  from Borneo to Sulawesi evolved  into different species east of Borneo. These figs then crossed Wallace’s Line East to West back into Borneo almost certainly in the gut of a flying fox or imperial pigeon.  These figs include;

Ficus gul

Ficus forstenii

Ficus septica

Ficus minahassae

Ficus glandifera