Fig. 1

a A schematic representation of a mutualistic network of interactions among plants producing fleshy fruits and the vertebrate frugivores that disperse their seeds in an Atlantic rainforest locality in SE Brazil (redrawn from Silva et al. 2005). The figure is a bipartite graph, i.e., a representation of the interactions (links) occurring among the species (nodes) in one set (plants) and the species in the other set (frugivorous animals), indicating the interactions that occur in this community. b The basic building blocks of many types of ecological interactions are pairwise relationships of mutual dependence or mutual influence among partner species. Each link in a (highlighted black links) actually embeds the relative dependence of a given plant (e.g., palmito Euterpe edulis) on the dispersal service of the frugivore species (e.g., the Jacutinga Aburria jacutinga or the Channel-billed toucan Rhamphastos vitellinus; dark arrow) and the reciprocal dependence of the frugivore on the fruit food resource provided by the plant (light arrow). In this case, the interaction is asymmetrical since the jacutinga depends heavily on palmito fruits while the bird has only a minor contribution to the overall seed dispersal of palmito, which is a keystone resource consumed by a diverse coterie of frugivores in the Atlantic forest (Galetti and Aleixo 1998)