The ant fauna of a dry rainforest in Australia's Northern Territory

Monsoon rainforests in northern Australia occur as small patches embedded within tropical savannas and contain ant faunas that differ markedly from those in the surrounding savannas. The ant faunas of 'wet' rainforests (associated with permanent water) are especially distinctive, containing specialist forest taxa of Indo-Malayan origin that are absent from the savanna. Here we describe the ant fauna of a 'dry' rainforest in the Casuarina Coastal Reserve, on the outskirts of Darwin in the Northern Territory (NT), and compare it with published ant faunas from monsoon forests elsewhere in the NT. We used Winkler extraction from leaf litter samples to survey 30 plots, recording 22 species from 14 genera. The most species-rich genera were 'Hypoponera, Monomorium, Pheidole' and 'Tetramorium', each with three species. The fauna was dominated by the functional groups Opportunists (including the introduced species 'Tetramorium lanuginosum' and 'T. simillimum'), Generalised Myrmicinae (including the introduced 'Monomorium floricola'), and Cryptic Species. There were no specialist forest taxa of Indo-Malayan origin. We collected a species of 'Arnoldius' that appears to be new to science. The biogeographical affinities of the species were primarily Widespread (45%) and Torresian (41%). Our comparison of monsoonal rainforests across the NT demonstrates that ant genus-level composition clearly differs between dry and wet rainforests. This can be directly related to the lack of seasonal moisture in dry rainforest, which is especially limiting for specialist cryptobiotic taxa inhabiting leaf litter.