a1 Programa de Pós-Graduação em Biologia Vegetal, Universidade Federal de Pernambuco, Avenida Professor Moraes Rego, s/n, Cidade Universitária, 50670-901, Recife, PE, Brazil
a2 Plant Ecology and Systematics, University of Kaiserslautern, PO-Box 3049, 67663 Kaiserslautern, Germany
a3 Departamento de Botânica, Universidade Federal de Pernambuco, Av. Prof. Moraes Rego s/no, 50670-901 Recife, PE, Brazil
Much of the ecological alteration faced by human-modified Neotropical forests can be assigned to edge effects, including the proliferation of some voracious herbivores such as leaf-cutting ants. However, the underlying mechanisms/impacts of tropical forest edge on herbivores performance and their foraging behaviour (e.g. dietary diversity) have rarely been investigated. The goal of this study was, therefore, to determine whether and how the annual diet (i.e. species richness, diversity and the relative proportion of pioneer versus non-pioneer species of plant materials) of Atta cephalotes colonies differs in the forest edge versus the interior zone of a large remnant of Atlantic forest in northeastern Brazil. Among the key results was a strong habitat effect on dietary diversity (explaining ca. 40–50% of the variation), which, in edge colonies, decreased approximately by one fourth compared to interior colonies (inverse of Simpson's index: 3.7±0.84 versus 4.99±0.95). There was a predominance of leaf fragments collected from pioneer species in the diet in both habitat (86% in edge and 80.4% in interior). Edge colonies collected proportionally more fragments from pioneer species than colonies located in the forest interior. Our results are the first to demonstrate an edge-mediated relaxation of dietary restrictions in leaf-cutting ants. These findings render robust support to previous evidence indicating the reduction of bottom-up forces as a key factor explaining both edge-induced hyper-abundance and increased herbivory of leaf-cutting ants in human-modified Neotropical landscapes.
(Accepted August 06 2010)
(Online publication November 01 2010)