Effects of Local Disturbance of Tropical Forests on Frugivores and Seed Removal of a Small-Seeded Afrotropical Tree

Abstract:  Small-scale, local disturbance of tropical forests, for example from selective logging, is widespread, but its effects on biodiversity and ecosystem function have rarely been studied. In 3 East African tropical rainforests, we investigated the effect of different levels of local forest disturbance on the frugivore community and on tree visitation and fruit removal rates of the small-seeded tree Celtis durandii. We quantified birds and primates in little and heavily disturbed sites, distinguishing between forest specialists, forest generalists, and forest visitors. We quantified frugivorous tree visitors and seed removal rates of C. durandii trees in the same sites. Forest disturbance reduced the species richness and density of the frugivore community and of forest specialists. Frugivorous species and individuals visiting the study trees were reduced significantly, which led to a marginally significant decline in fruit removal by all frugivores and a significant reduction in removal by forest specialists. Reduction in fruit removal by forest specialists was not compensated for by increases in removal by forest generalists or visitors. Results did not differ among the 3 rainforests, which suggests they were consistent at a regional scale. So local forest disturbance led to a loss of frugivores and their seed removal services. This suggests that large-seeded tree species and trees with small fruits are losing seed dispersers. Thus, local forest disturbance appears to have a more general negative impact on frugivores and their seed dispersal services than anticipated previously.