Potential Keystone Plant Species for the Frugivore Community at Tinigua Park, Colombia

Abstract

Different practical problems restrict the possibility of rigorously testing the role of plants as keystone species in tropical forests, and therefore we do not yet know the impacts that could result from their removal. Currently, the criteria used to suggest keystone plant species in tropical forests include an assessment of their importance in supporting frugivore communities during periods of fruit scarcity, their reliability during these periods, their abundance, and the number of species that feed on their fruits. However, even for resources that match these criteria it has been shown that the density of these plant species is not necessarily correlated with the abundance of frugivores, so their relevance is still an open question. In this study I use information on feeding behavior and phenological data collected over three years in Tinigua National Park, Colombia, to identify potential plant keystone resources for the fruiteating animals. Among 29 plant species that produced fruit or were consumed in periods of fruit scarcity, I found virtually no case of a species that could maintain a large proportion of the frugivore community. Plant species previously suggested playing keystone roles, such as palms and figs, were included in the list. But palms did not support a very large coterie of frugivores and figs were reliable only at the genus level. The fact that only 3 of the 29 species suggested to play keystone roles at Tinigua were present in a recent review of the potential keystone resources in Neotropical forests (Peres, 2000), suggests that species playing important roles in one community may be unimportant in other localities. I conclude that postulating keystone resources in tropical forests might lead to strategies to protect local animal guilds, but it is difficult to find species that could support the majority of frugivores in complex communities and it is naïve to generalize about their roles across localities. I suggest that the bulk of frugivores in Tinigua (i.e. primates) may use fat reserves accumulated during periods of fruit abundance to survive the lean period, and therefore keystone resources might not be restricted to particular seasons.