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Australian Ant Distribution Patterns
Australia is a large and diverse continent with habitats ranging from dry, sandy deserts to lush tropical rainforests. These different habitats form distinct patterns across the Australian landscape, patterns which have a strong impact on the distribution of ants.
Many ant genera are found only in rainforests in the warm, high rainfall areas along the northern and eastern coasts (see map below). In fact, about 23 of the 101 Australian genera are limited to coastal Queensland and north-eastern New South Wales (see locations map at bottom). If we add to these rainforest habitats the higher rainfall forests and Mediterranean climate regions of southern New South Wales, Victoria, Tasmania, southern South Australia and south-western Western Australia, the number of genera limited to these regions grows to about 50, or nearly half of all known Australian genera. Additionally, more ant genera have been found at certain Queensland rainforest sites than any other Australia site of comparable size, with up to 76 genera being recorded. In contrast to this, the dry arid zone of central Australia is occupied by only about 25 genera. None of these genera are limited to the arid zone as all occur in higher rainfall areas nearer the coasts. It is also worth noting that only a single genus, Nebothriomyrmex, is restricted to Western Australia and no genera are limited to Tasmania.
This general pattern seen in ant genera is similar to the pattern seen in many other groups of animals: the greatest richness is found in moist, forested areas nearer the coast and only a limited subset extends into the inland arid areas. This pattern is so strong that the ant fauna of extreme south-western Australia (e.g. in the vicinity of Perth) is more similar to that of the moist south-east than it is to that of the much closer northern Western Australia (e.g. the Kimberley region).
At the species level, the pattern is considerably different to that seen for genera. With the exception of alpine and highly disturbed areas, many regions of Australia have similar numbers of species, commonly between 80 and 100 belonging to 15 to 50 genera. This is because rainforest genera tend to contain only a small number of species while many of the arid zone genera include many species. Thus it would seem that while relatively few genera have been able to invade the Australian arid zone, they nonetheless have been very successful, with as many species occurring in these areas as in forested areas, including tropical rainforests. Locations with the largest numbers of species are likely to be in one of two regions: either in the semi-arid transition zones where the faunas of the moist south-eastern forests mix with those of the arid areas, or in the northern arid zone where the northern tropical fauna mixes with that of the more southern arid zone. It is possible that up to several hundred species may be found at locations in these regions. It is surprising that in most regions of the world the highest species richness occurs in rainforest areas, while in Australia the richest areas are much more arid.