Pulau Maratua is the largest island of a group of c. 20 small isolated islands known as the Derawan islands, c. 51 km off the cost of East Borneo at the junction of 3 separate floral regions (1) Borneo/Sundaland, (2) Sulawesi to New Guinea -Wallacea and (3) The Philippines.
Each region has distinctively different plants and animal life. Borneo is by far the closest large island to Maratua, yet 5 out of the 9 species of figs present on Maratua and the Derawan islands must have originated from Sulawesi or the Philippines
|Fig species||Distance from Maratua||Origin of Maratua figs|
|Sulawesi||81||270 km||1 + 4 ?|
|Philippines||87||284 km||1+ 4 ?|
Pulau Maratua is an atoll, the remnant of an extinct volcano and has never been joined by a land bridge to Borneo. The shortest sea crossing from Borneo to Maratua is approx. 51 km. One would expect that the figs of Maratua would all be Bornean in origin but this is not the case.
According to Berg’s (2005) Flora Malesiana monograph on figs, Sulawesi hosts 81 species of native figs and Borneo hosts 141 native figs.
The relatively small island of Maratua (c. 2,000 ha) hosts at least 9 species of figs of which one Ficus glandifera can only have come from Sulawesi.
Finally there is a curious species which may be wrongly identified but which is very unlikely to have arrived from Borneo.
One would expect that as Maratua is relatively much closer to Borneo (51 km) compared to Sulawesi (270 km) and the Philippines (284 km) that the Maratua figs would all have originated from Borneo but in fact over half appear to have arrived from either Sulawesi or the Philippines.
One possible explanation is that the most important dispersers of island figs, imperial pigeons and flying foxes are nomadic island specialists and are more likely to fly between islands than from the islands to the mainland. Thus very long distance dispersal is mostly from island to island not from the mainland to islands.
An alternative (more likely) explanation is that many additional species of Bornean forest figs have arrived on Maratua from Borneo over the last many thousands of years transported by bats and pigeons but they have been unable to to survive the harsh island conditions including periodic droughts. Only figs and fig wasps which are island specialists are tough enough to survive.