ANT COMMUNITIES IN THE GULF REGION OF AUSTRALIA SEMIARID TROPICS - SPECIES COMPOSITION, PATTERNS OF ORGANIZATION, AND BIOGEOGRAPHY

The ant communities of nine sites near Lawn Hill (540 mm mean annual r ainfall) in semi-arid north-western Queensland are documented, and com pared with the known faunas of arid, semi-arid and seasonally arid sit es elsewhere in Australia. The sites were surveyed primarily by pitfal l trapping, during April (end of wet season) 1991, September (late dry season) 1991, and February (mid-wet season) 1992. A total of 111 ant species was recorded, with the most common being Iridomyrmex spp. and Rhytidoponera rufithorax. The richest genera were Melophorus (26 speci es), Monomorium (17), Iridomyrmex (16) and Camponotus (10) and Pheidol e (10). The maj or functional groups were Dominant Dolichoderinae (Iri domyrmex spp.; 14% of the total number of species, 47% of the total nu mber of ants in traps), Hot-climate specialists (mostly Melophorus spp .; 39%, 22%) and Generalised Myrmicinae (mostly Monomorium and Pheidol e spp.; 20%, 11%). Multivariate analysis indicated that site differenc es in species composition were related primarily to landform, geology and soil type. Comparisons with other ant faunas show the Lawn Hill fa una to have closer affinities with those of the central arid zone than with those of high rainfall areas of the seasonal tropics. The arid-z one characteristics of the Lawn Hill fauna include a high proportion ( 38%) of Eyrean species, a high mean number of species per genus (6.5), and a very high combined representation of Iridomyrmex, Melophorus an d Camponotus (45% of the total number of species, 69% of the total num ber of ants in traps).