The terrestrial vertebrate fauna of the krakatau islands, sunda strait, 1883-1986

Abstract

The results of terrestrial vertebrate collecting on the Krakatau Islands, Sunda Strait, during La Trobe University-L.I.P.I. expeditions in 1984, 1985 and 1986 are reported and previous records from the islands are consolidated and reviewed. Since the 1883 eruption of Krakatau, 15 species of terrestrial vertebrates (13 reptiles and 2 mammals) have been recorded from the Krakatau Group. Two of the species records (Crocodylus porosusandCosymbotus platyursareonly incidental but the remaining thirteen species have at some stage established breeding populations on one or more islands. In the first 50 years up to 1933, ten species (eight reptiles and two mammals) reached the islands, eight of which (Hemidactylus frenatus, Lepidodactylus lugubris, Emoia atrocostata, Mabuya multifasciata,Varanus salvator, Python reticulatus, Rattus rattusandRattus tiomanicus) had established breeding populations. Results of collections made over the period 1982-1986 showed that two of the species (L. lugubris and E. atrocostata) with breeding populations in 1933 had become extinct, whereas five new species (Gekko gecko, Gekko monarchus, Hemiphyllodactylus typus, Chrysopelea paradisiandRamphotyphlops braminus) have reached the islands and established breeding populations. Therefore at the end of 100 years, eleven species of terrestrial vertebrates have extant breeding populations on one or more islands in the Krakatau group; two species have become extinct; and two species have incidental records. Significant ecological changes in the development of the present day terrestrial fauna are discussed. These include canopy closure of the forests and continual marine erosion of the coasts that together have eliminated most of the open habitats on Rakata, Sertung and Panjang; heavy ash falls from volcanic eruptions on Anak Krakatau that have periodically disrupted successional stages and habitats on Sertung, Panjang and Anak Krakatau. The dispersal of terrestrial vertebrates in the Sunda Strait is discussed in the light of the heavy boat traffic and the predominant southwest ocean currents. It is concluded that dispersal by human agency on boats is highly significant, seven of the 15 recorded species (46%) being most likely to have reached the islands in this way; and the prevailing southwest flow of water in Sunda Strait makes Sebesi and Sumatra the probable source areas for the eight species most likely to have dispersed on ocean currents by swimming or rafting. Anak Krakatau, the volcanic island that became permanent in Aug. 1930, has three species of terrestrial vertebrates (H. frenatus, V. salvator. andC. paradisi) all of which have established breeding populations on Rakata, Sertung and Panjang. The early arrival ofH. frenatusandV. salvatorand their present abundance on all four islands distinguishes them as the most successful terrestrial vertebrate colonizers of the Krakatau group.