Leaf-cutting ant populations profit from human disturbances in tropical dry forest in Brazil

Abstract:

Anthropogenic disturbance often results in the proliferation of native species of particular groups that leads to biotic homogenization. Leaf-cutting ants are an example of such winner organisms in tropical rain forests, but their response to disturbance in dry forests is poorly known. We investigated Atta colony density in areas of tropical dry forest in Brazil with different distance to roads and vegetation cover. Atta colonies were surveyed in 59 belt transects of 300 × 20 m, covering a total area of 35.4 ha. We found 224 Atta colonies, 131 of which were active and belonged to Atta opaciceps (87 colonies, 2.45 ha ⁻¹), A. sexdens (35 colonies, 0.98 ha ⁻¹) and A. laevigata (9 colonies, 0.25 ha ⁻¹). The density of active colonies sharply decreased from 15 ± 2.92 ha ⁻¹ in the 50-m zone along roads to only 2.55 ± 1.65 ha ⁻¹ at distances up to 300 m. The reverse pattern was observed for inactive colonies. Active Atta colonies preferentially occur in areas with low vegetation cover, while inactive colonies prefer areas with high vegetation cover. We demonstrate for the first time that anthropogenic disturbances promote the proliferation of leaf-cutting ants in dry forest in Brazil, which may affect plant regeneration via herbivory and ecosystem engineering as demonstrated for rain forests.