Biogeography of the ant fauna of the Tiwi Islands, in northern Australia's monsoonal tropics

Abstract

This paper describes the biogeography at the species level of ants from the Tiwi Islands, and represents the first such analysis for any region in Australia. The Tiwi Islands are located 20 km off the mainland coast near Darwin in northern Northern Territory, and include Australia's second largest insular landmass after Tasmania. The islands receive the highest mean annual rainfall (up to 2000 mm) in monsoonal northern Australia, and they are the closest part of the Australian landmass to south-east Asia. On the basis of ~1300 species records, we list 154 species (including nine introduced) from 34 genera. The richest genera are Polyrhachis (20 species), Monomorium (15), Camponotus (14), Pheidole (12), and Iridomyrmex (11). In all, 66% of the native Tiwi species belong to Torresian (tropical) species groups, which is considerably higher than the 44% for Australia's monsoonal ant fauna as a whole. Fifteen Tiwi ant species are not known from mainland Australia. These include a species of Anonychomyrma, which is the only record of the genus in monsoonal Australia, Polyrhachis debilis, the only representative of the sub-genus Cyrtomyrma known from north-western Australia, and the only species of the araneoides group of Rhytidoponera known from the Northern Territory. Unfortunately, the Tiwi ant fauna also includes the exotic invasive species Pheidole megacephala, which represents a serious conservation threat.