Invasive Species Compendium

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Abstract

Ants collected on the Krakatau Islands 100 years after the great eruptions.

Abstract

Ant fauna was surveyed in 1982 on the Krakatau Islands, Indonesia, which are said to have been sterilised by the great eruptions in 1883. A total of 79 ant species belonging to 37 genera in 7 subfamilies were collected from the four islands, Rakata, Sertung, Panjang and Anak Krakatau. Two species of Rhoptromyrmex were added in 1985 by the Australian team. Actual species numbers for the four major survey periods are: 21 species (1908), 34 (1919-21), 39 (1929-32) and 81 (1982-85). The actual species number was still steadily increasing, without any sign of reaching an equilibrium species number. Some species preferring disturbed conditions were only collected during earlier periods, and not found in 1982. Bothriomyrmex wroughtonii, Polyrhachis dives, Tetraponera rufonigra etc. were commonly found on larger islands like Rakata during earlier periods, but in 1982 they were confined to Anak Krakatau that had been frequently disturbed by volcanic activity and dominated by poor vegetation, probably due to the development of forests on the former islands. On the other hand, more versatile species like Anoplolepis gracilipes, Oecophylla smaragdina had been more persistently present on every island. Up to the 1930s no species of ant with wingless queens and performing dependent colony founding (fission) had been found on this island group. The discovery of Leptogenys in 1982 suggests that a fission-performing ant species actually colonised an isolated island ca. 40 km apart from adjacent landmasses within 100 years.