The value of ants as early warning bioindicators: responses to pulsed cattle grazing at an Australian arid zone locality

The value of ants as bioindicators of incipient environmental change in rangeland condition was assessed on a local scale in the South Australian arid zone. The sensitivity of ants to intense pulses of unsustainable grazing was tested, in order to identify species, functional groups or community variables that could be used as indicators of more typical grazing pressure. Genera represented by the largest number of species were Iridomyrmex, Melophorus, Camponotus andMonomorium . A significant decrease in captures of Rhytidoponera metallica was recorded on swales, whereas theIridomyrmex sp.(bicknelli) group increased on dunes relative to controls following grazing. The Generalized Myrmicinae functional group increased on swales, and Hot-climate Specialist ants increased on dunes, after grazing. Several other species and functional groups responded qualitatively but not significantly. However, neither overall ant abundance and richness, nor the abundances of most of the common species and functional groups responded significantly to grazing in this local scale experiment, which rendered ants of limited use as early warning indicators of unsustainable management. The use of ants for this purpose is constrained by a lack of knowledge of the ecology of individual ant species, particularly of the less common and more localized species that are likely to be most sensitive to disturbance.