RESTRICTED POLLINATION ON OCEANIC ISLANDS - POLLINATION OF CEIBA-PENTANDRA BY FLYING FOXES IN SAMOA

The very low diversity of animal pollinators on remote oceanic islands can act as a potent biotic filter to potential plant immigrants. To assess the relative difficulties faced by colonizing plant species, we studied the pollination ecology of kapok, Ceiba pentandra (Bombacaceae), a widespread aboriginal introduction to Pacific islands. The Samoan form of this tree is self-fertile, but requires pollination for fruit set. In continental areas C. pentandra attracts a diverse assemblage of pollinators, but in Samoa it is pollinated only by Pteropus tonganus (Megachiroptera: Pteropodidae)-an example of a plant exclusively dependent on one bat species for pollination. The pollination system is dystrophic, however, since foraging flying foxes may destroy up to 50 percent of C. pentandra flowers and developing fruits. Though resource defense is regarded as rare in nectarivorous bats, P. tonganus vigorously defends small feeding territories on the rich, but readily depleted, C, pentandra nectar resource. This intraspecies conflict probably shapes patterns of pollen transfer within and among trees, and enhances cross-pollination. Our study highlights the importance of conserving pollinators in remote oceanic islands with depauperate pollinator faunas.