Journal of Ecology 2002 90 , 517 – 528 © 2002 British Ecological Society Blackwell Science, Ltd Ants affect the distribution and performance of seedlings of Clusia criuva, a primarily bird-dispersed rain forest tree LUCIANA PASSOS and PAULO S. OLIVEIRA* Departamento de Botânica, C. P. 6109, Universidade Estadual de Campinas, 13083–970 Campinas SP, Brazil, and *Departamento de Zoologia, C. P. 6109, Universidade Estadual de Campinas, 13083–970 Campinas SP, Brazil Summary 1 We studied the dispersal system of the tree Clusia criuva (Clusiaceae) in a tropical rain forest in south-east Brazil. An observational/experimental approach was adopted to estimate the probability of transitions between consecutive stages in the recruitment process (i.e. fruit production and removal by birds, ant–seed interactions on the forest floor, seed germination, and establishment and early survival of seedlings). 2 Clusia trees produce hundreds of capsules with small lipid-rich arillate seeds. Crop size ranges from 393 to 3709 capsules per tree. Birds (14 species) eat 83% of the diaspores on the tree, while the remaining 17% fall to the ground and are removed by ants (16 species). 3 Ants remove 89% of the fallen diaspores and 98% of the seeds found in bird faeces. Ponerine ants (Odontomachus, Pachycondyla) carry the diaspores to their nests, while small myrmicines (Pheidole, Crematogaster) remove the aril where found. Aril removal by ants and removal of seeds from bird defecations increase germination success in C. criuva. 4 Seedlings are more frequent close to ponerine nests than in control areas without such nests. Early seedling survival (1 year) in nests of Pachycondyla striata is greater than in control areas. Soil samples from nests of P. striata also had higher concentrations of total nitrogen and phosphorus than random soil samples. 5 This is the first study to demonstrate the combined effects of ants on the distribution and survival of seedlings of a primarily vertebrate-dispersed plant in a tropical forest. Key-words: ants, birds, Brazil, Clusia, Clusiaceae, seed dispersal, seedling survival, tropical rain forest Journal of Ecology (2002) 90, 517– 528 Introduction Seeds that are dispersed primarily by frugivorous vertebrates may also be secondarily distributed by ants (reviewed by Böhning-Gaese et al . 1999). The ecological consequences of ant activity in such two- phase dispersal systems are still poorly understood (but see Kaufmann et al . 1991; Pizo & Oliveira 1998; Böhning-Gaese et al . 1999), unlike those of myrmeco- chorous (i.e. ant-dispersed) species with elaiosome- bearing seeds (e.g. Hanzawa et al . 1988; Hughes & Westoby 1992a,b; Garrido et al . 2002). Typical myrmecochorous species occur worldwide but are especially common in arid Australia and South Africa, and temperate forests (Beattie & Culver 1981; Milewski & Bond 1982; Beattie 1985). Although myrmecochory can be an important dispersal strategy for some plant taxa in neotropical forests (Horvitz & Beattie 1980; Passos & Ferreira 1996), nearly 90% of dicots there have fleshy fruits and rely on vertebrate frugivores for seed dispersal (Frankie et al . 1974). Many diaspores are found on the forest floor (Jordano 1993), where they have fallen, been dropped by frugivores (Howe 1980; Laman 1996) or deposited in vertebrate faeces (Kaspari 1993; Pizo & Oliveira 1999), and the abundance of litter-foraging ants (Hölldobler & Wilson 1990) suggests that ant–diaspore interactions may be common. Indeed, a 2-year survey carried out in the Atlantic forest of south-east Brazil recorded 886 ant– diaspore interactions involving 36 ant species and 56 plant species (Pizo & Oliveira 2000). Recent studies in neotropical areas have shown that ants can rearrange the seed shadow generated by vertebrate dispersers (Roberts & Heithaus 1986; Kaspari 1993), affect seed bank dynamics (Levey & Byrne 1993), facilitate seed germination (Oliveira et al . 1995; Leal & Oliveira 1998; Pizo & Oliveira 1998) and promote seedling establishment Correspondence: Paulo S. Oliveira, Departamento de Zoologia, Universidade Estadual de Campinas, C. P. 6109, 13083–970 Campinas SP, Brazil (fax 55 19 32893124; e-mail pso@unicamp.br).