Community aspects of frugivory in tropical forests

Abstract

This chapter considers the ways phenological cycles of resource production interact with frugivore communities in tropical forests. The birds and mammals that feed primarily on plant reproductive parts (seeds and pulp) at an undisturbed Amazonian locality in southeastern Peru make up a biomass of about 1,400 kg/km² of mammals and 160 kg/km² of birds. In order of importance, the major groups of mammals are primates, rodents and peccaries, and of birds, are cracids, tinamous and toucans. About a third of the total biomass consists of seed predators which feed mostly on the ground and two thirds of pulp eaters which feed mainly in trees.

The production of fruits and seeds by the forest at this site follows a two-peaked annual cycle of high amplitude. During the low point in this cycle, a 3–4 month period covering the transition from wet to dry seasons, the production of plant reproductive parts falls below the estimated consumption rate of the frugivore community. In response, many animals modify their diets by switching to a limited number of alternate food resources. In all, only 12 plant species, here termed ‘keystone plant resources’, sustain as much as 80% of the animal biomass through the annual period of scarcity. The abundance of these keystone resources appears to set the carrying capacity of the forest for frugivorous animals, and in turn, many of these frugivores appear to possess adaptations for harvesting particular keystone resources.

At the end I review the available information on phenological patterns of fruit production in tropical forests around the world in an effort to extend the generality of these results to other areas of the tropics.