CHANGES IN LEAF-CUTTING ANT POPULATIONS (FORMICIDAE, ATTINI) AFTER THE CLEARING OF MATURE FOREST IN BRAZILIAN AMAZONIA

This study investigates how clearing of mature forest for agriculture and ranching in Amazonia affects leaf-cutting ant populations (Atta an d Acromyrmex). Data on ant nest densities in mature forest, and in you ng (2-5 years) and older (6-18 years) second growth forests was obtain ed from five sites in the central and eastern regions of Brazilian Ama zonia. Clearing of mature forest strongly increased the density of nes ts 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 dec lined with growth of secondary forest, but nest densities in older sec ondary were still higher than in mature forests. Secondary forests wer e usually dominated by species of leafcutting ant not originally prese nt in the mature forest. Evidence is presented to show that deforestat ion in Amazonia is increasing the geographical range of some leaf-cutt ing ant species.