Journal of Tropical Ecology (2009) 25:223–227. Copyright © 2009 Cambridge University Press doi:10.1017/S0266467409005823 Printed in the United Kingdom SHORT COMMUNICATION Decreasing abundance of leaf-cutting ants across a chronosequence of advancing Atlantic forest regeneration Paulo S. D. Silva ∗, †, Ana G. D. Bieber ∗, †, Inara R. Leal‡, Rainer Wirth§ and Marcelo Tabarelli‡ ,1 ∗ Programa de P ´ os-Graduac ¸˜ ao em Biologia Vegetal, Universidade Federal de Pernambuco, Recife, PE, 50670-901, Brazil † Programa de P ´ os-Graduac ¸˜ ao em Ecologia, Instituto de Biologia, Universidade Estadual de Campinas, Campinas, SP, 13083-970, Brazil ‡ Departamento de Bot ˆ anica, Universidade Federal de Pernambuco, Recife, PE, 50670-901, Brazil § University of Kaiserslautern, Department of Plant Ecology & Systematics, Postfach 3049, 67653 Kaiserslautern, Germany (Accepted 29 December 2009) Key Words: Atta cephalotes, Brazil, bottom-up control, colony density, forest regeneration, pioneer species Leaf-cutting ants (species of Atta and Acromyrmex) are dominant herbivores and play a key role as ecosystem engineers of tropical and subtropical America (Fowler et al. 1989, Weber 1972). Not only are they among the most polyphagous and voracious herbivorous insects, cutting up to 15% y −1 of the leaf standing crop (Urbas et al. 2007, Wirth et al. 2003), but also they strongly affect the light environment and the nature of plant assemblages via ant-nest-mediated disturbances (Farji- Brener & Illes 2000, Hull-Sanders & Howard 2003, Moutinho et al. 2003). Some leaf-cutting ant species have turned into an omnipresent feature of present- day neotropical landscapes and a wealth of studies has documented their abundance to drastically increase with increasing agricultural land use, disturbance and deforestation/fragmentation (Fowler et al. 1986, Jaffe 1986, Terborgh et al. 2001, Vasconcelos & Cherrett 1995, Wirth et al. 2007). In view of their ecosystem engineering capacity and the ever-increasing conversion of tropical forests into agricultural landscapes (Wright 2005), it has been concluded that disturbance-driven accumulation of Atta colonies leads to far-reaching and deleterious consequences in present-day neotropical landscapes (Wirth et al. 2008). But what about the opposite scenario of regenerating forests? Is disturbance-mediated hyper- abundance of leaf-cutting ants a reversible phenomenon? We believe that this question is highly relevant because (1) knowledge of the dynamics of leaf-cutting ant populations during forest regeneration is lacking and (2) natural secondary succession has become a widespread phenomenon after land is abandoned or temporarily fallowed (Wright 2005). In the Brazilian Amazon during 1 Corresponding author. Email: mtrelli@ufpe.br the 1990s, for example, secondary forests have reclaimed 31% of the once deforested land (Perz & Skole 2003). Here we expect that the abundance of leaf-cutting ant colonies declines while that of inactive/abandoned nests increases with increasing age of regenerating forests, based on the assumption that the availability of highly palatable tree species decreases due to the successional replacement of pioneers by shade-tolerant forest species (Guariguata & Ostertag 2001). As a mechanistic corroboration of this hypothesis, we further predict that leaf-cutting ant foraging areas should increase with regeneration age because foraging ants have to travel a greater distance to find and collect more sparsely distributed food plants (see Shepherd 1985 for dietary diversity in early versus late secondary forests, and Urbas et al. 2007 for foraging areas along pioneer- dominated edge versus forest interior habitats supporting this conclusion). To test these hypotheses we assessed a large (3500 ha) and well-preserved remnant of the Atlantic forest in north-east Brazil – the Coimbra forest (8 ◦ 30 ′ S, 35 ◦ 52 ′ W). This privately owned fragment is situated on a low-altitude plateau (300–400 m asl), and completely embedded into a stable matrix consisting of sugar cane plantations (Oliveira et al. 2004). An average annual rainfall of ∼2000 mm supports an evergreen, lowland forest. Leguminosae, Lauraceae, Sapotaceae, Chrysobalanaceae, Euphorbiaceae and Lecythidaceae hit the highest scores of tree species richness (Grillo et al. 2006). In 2005, we assessed Atta cephalotes colonies within a total of 17 secondary-forest patches (ranging in size from 0.53 to 7.4 ha, with a total area of 43.3 ha), which consisted of formerly clear-cut sites within flat, core areas of the Coimbra forest. Although embedded in the same matrix of mature forests, these second-growth