Ants affect the distribution and performance of seedlings of Clusia criuva, a primarily bird-dispersed rain forest tree

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 (I 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.