Abiotic factors affecting the foraging activity and potential displacement of native ants by the invasive African big-headed ant Pheidole megacephala (FABRICIUS, 1793) (Hymenoptera: Formicidae)

Abstract

The African big-headed ant Pheidole megacephala is an invasive non-native species that threatens native ecosystems throughout many regions of world. As it spreads into new areas, P. megacephala becomes abundant and reduces the diversity of other insects, particularly native ants. Although the consequences of P. megacephala invasion have been well studied, the factors correlated with the foraging success of P. megacephala remain unclear. We examined the foraging activity and potential displacement of native ants by P. megacephala in relation to physical conditions in disturbed urban bushland. The foraging activity of P. megacephala was related to both seasonal and daily temperatures. The relative proportion of P. megacephala that recruited to baits was higher during warm seasons, and the abundance of P. megacephala was higher in the morning than in the afternoon, which correlated with the displacement of native ant species at these times. By contrast, native ants dominated baits at either very low or very high temperatures, with almost no co-occurrence of native ants with P. megacephala. In laboratory experiments, high temperatures had a strong negative effect on worker survival of P. megacephala, particularly under low moisture conditions, explaining abiotic preferences observed in the field. A competing native ant species Iridomyrmex chasei had significantly greater survival under high temperature and low moisture conditions. This study thus indicates that abiotic conditions can modify the outcome and dynamics of P. megacephala invasion and foraging interactions with native ants, thereby affecting local community dynamics.