THE ROLE OF FRUGIVOROUS BATS AND BIRDS IN THE REBUILDING OF A TROPICAL FOREST ECOSYSTEM, KRAKATAU, INDONESIA

Krakatau provides a case study in tropical forest rebuilding following sterilization of the islands in 1883 by volcanic eruptions. On the basis of historical and recent records, the roles of frugivorous birds and bats in plant colonization and spread are assessed with reference to the interior forest communities. It is established that the islands are within the effective seed-transport range of members of both the avifauna and bat fauna and it is argued that it is parsimonious to assume a role for both taxa in introducing small-seeded species. For instance, the most successful genus of plant colonists, Ficus with twenty-four species, is attractive to both groups of dispersers. Larger seeds which cannot be ingested by bats must have been introduced by birds, with the exception of diplochorous, primarily sea-dispersed species (or human introductions). The largest-seeded partially-zoochorous species are bat-spread trees. Birds have a dispersal role for a more balanced range of plant growth forms than do bats, for which available records indicate a restriction largely to trees and shrubs. Early this century savanna was predominant, but following the establishment of scattered patches of trees and shrubs, forest closure occurred very rapidly, almost exclusively involving zoochorous trees, notably Ficus spp. For the period 1883-1992 a total of 124 species of plants are identified as probably having been introduced endogenously by birds and bats and a further forty-nine partially zoochorous species have been recorded. Birds and bats are argued to have partially overlapping yet complementary roles as dispersers. The implications of these observations for restoration ecology and forest conservation are discussed.