Responses of Ground-Foraging Ant Communities to Three Experimental Fire Regimes in a Savanna Forest of

Ants were sampled using pitfali traps in two replicate 1 ha plots of each of three experimental fire treatments (annually burned, biennially burned, and unburned for over 14 years) in a eucalypt-dominated savanna of tropical northern Australia. The ant fauna was extremely diverse, with 81 species from 24 genera recorded. Species were classified into functional groups based on habitat requirements and competitive interactions, with the most important groups being dominant species of Iridomyrmex (11 species, 14-63% total ants in traps); generalized myrmicines (mostly species of Monomorium and Pheidole; total of 22 species, 1 1-61% total ants in traps); hot climate specialists (species of Melophorus, Monomorium ("Chelaner") and Meranoplus; total of 14 species, 1-16% total ants in traps); cryptic species (many genera; total of 13 species, 2-27% total ants in traps); and, opportunists (mostly species of Rhytidoponera and Tetramorium; total of 11 species, 3-12% total ants in traps). Ant communities in the annually burned plots were characterized by relatively high numbers of dominant Iridomyrmex, hot climate specialists and opportunistic Rhytidoponera aurata, and low numbers of generalized myrimicines and cryptic species. The reverse was true for unburned plots. Many species were common under one fire regime, but were rarely or never recorded under the other. These differences were attributed to structural changes in the habitat caused by fire, and in particular to the levels of litter accumulation and insolation on the ground. These changes influenced ants directly, but also had important indirect effects through their influence on the abundance of dominant Iridomyrmex, and therefore on competitive interactions. The ant communities in the biennially burned plots were generally intermediate to those of the unburned and annually burned plots. However, one was more similar to those in the annualiy burned plots, while the other resembled those in the unburned plots. These results demonstrate that different fire regimes have a major influence on one of the most important faunal groups in tropical savannas, and this has important implications for conservation management in these ecosystems.