The use of fruits and seeds by ants in the Atlantic forest of southeast Brazil

Given the abundance of litter-foraging ants and fallen fleshy diaspores on the door of tropical forests, interactions involving them should be common and may render important consequences fur the biology of the diaspores. In this study we surveyed the interactions between ants and non-myrmecochorous diaspores along a 5-km transect in a lowland Atlantic rain forest of southeast Brazil. A diaspore is defined as any seed, fruit, or infructescence that constitutes the unit of dispersal of the plant. During two years of monthly samplings of naturally fallen diaspores, 886 ant-diaspore interactions involving 36 ant species and 56 different species of diaspores (range = 0.05-29.5 g) were recorded. The number of interactions was significantly and positively correlated with rainfall but not with mean temperature. The number of ant species recorded in the interactions was positively associated with both rainfall and temperature. Lipid-rich diaspores attracted a larger ant assemblage than those with lower contents of lipids. The seasonal pattern for ant-diaspore interactions in the Atlantic rain forest is predicted by well known seasonal patterns in ant activity and diaspore production. Other factors that also may affect the observed pattern are the massive and episodic fruiting of some plant species in which diaspores are especially attractive to ants, and a preference for lipid-rich arillate seeds. Interactions between ants and fallen non-myrmecochorous diaspores may be especially common in lowland rain forests in which the abundance of ants is coupled with the year-round availability of fleshy diaspores.