THE PRIMATE COMMUNITY OF THE LOPE RESERVE, GABON - DIETS, RESPONSES TO FRUIT SCARCITY, AND EFFECTS ON BIOMASS

The diets of all diurnal primates (Gorilla g. gorilla, Pan t. troglody tes, Mandrillus sphinx Colobus satanas, Cercocebus albigena, Cercopith ecus nictitans, C. pogonias, C. cephus) in the Lope Reserve, central G abon, are described from qualitative and quantitative data collected o ver 10 years. A total of 397 foods were recorded, of which 91% were fr om plants. The diets of seven of the eight species were numerically do minated by fruit, the exception being Colobus satanas with a diet domi nated by seeds. When proportion of feeding time was examined, fruit re mained the dominant food class for six species, while Cercocebus albig ena, like the black colobus, spent most time feeding on seeds. The num ber of foods recorded per species ranged from 46-220, but dietary brea dth of the four species that have not been subjects of detailed study was certainly underestimated. Almost half of the foods (46%) were eate n by only one species, and only four (1%) were recorded for all eight species. At Lope, fruit is scarce for 2-3 months during the annual dry season, and fruit crop failures can prolong this period of scarcity t o as many as 8 months in some years. When fruit is scarce, the diets o f all species changed to include more nonfruit foods, but chimpanzees and the three species of guenons maintained a fruit dominated diet. Th e total biomass of the Lope primate community is 374 kg/km(2), which i s low compared to other sites in tropical Africa. Within the Lope comm unity, biomass correlates negatively with degree of frugivory, suggest ing that fruit availability may be critical, but this does not explain the low total biomass compared to other sites. Neither floristic dive rsity nor the composition of the primate community at Lope can account for the low biomass. While historical events such as climate-induced changes in forest cover, disease, or impact of human activities cannot be ruled out, we conclude that the most likely explanation of low pri mate biomass is the occurrence of an ecological ''catastrophe'' in the fairly recent past from which populations have not yet recovered. We believe that the most likely scenario was climate-mediated disturbance of flowering of important fruit food species. Prolonged fruit scarcit y would have caused mortalities and affected the most frugivorous spec ies more severely. (C) 1997 Wiley-Liss, Inc.