Changes in leaf‐cutting ant populations (Formicidae: Attini) after the clearing of mature forest in Brazilian Amazonia

Abstract

This study investigates how clearing of mature forest for agriculture and ranching in Amazonia affects leaf‐cutting ant populations (Atta and Acromyrmex). Data on ant nest densities in mature forest, and in young (2–5 years) and older (6–18 years) second growth forests was obtained from five sites in the central and eastern regions of Brazilian Amazonia. Clearing of mature forest strongly increased the density of nests and altered the species present. Acromyrmex nest densities were up to 20 times higher in young secondary than in mature forests, whereas the density of Atta nests increased up to 30 times. Nest densities declined with growth of secondary forest, but nest densities in older secondary were still higher than in mature forests. Secondary forests were usually dominated by species of leafcutting ant not originally present in the mature forest. Evidence is presented to show that deforestation in Amazonia is increasing the geographical range of some leaf‐cutting ant species.