Comparative structure of harvester ant communities in arid Australia and North America

In the Australian arid zone, the species richness of ants is greater and that of mammalian granivores is less than in North American deserts. This study aimed to determine if the structure of harvester ant communities differs from that seen in North American deserts, focussing on differences related to the paucity of rodents. We tested three hypotheses: (1) because there are fewer rodents, Australian harvester ants should be more abundant and diverse in local habitats than in North American deserts of similar productivity; (2) because the absence of rodents would allow ants to use larger seeds that are preferred by rodents in North America, Australian ant communities should include a larger size range and contain larger workers; and (3) that apart from differences resulting from a paucity of rodents, Australian and North American communities would be convergent in characteristics of community structure resulting from competition. We sampled 19 communities across a climatic gradient in the Australian arid zone and compared the results with data previously obtained for 10 North American communities.