Impact of seed dispersal of red howler monkeys Alouatta seniculus on the seedling population in the understorey of tropical rain forest

1 Seedlings of six plant species (Parahancornia fasciculata, Virola michelii, Minquartia guianensis, Quiina obovata, Chrysophyllum lucentifolium, Pouteria torta ssp. glabra), the ripe fruits of which are exploited by howler monkeys Alouatta seniculus, were surveyed in a primary tropical forest at Nourague Station, French Guiana, under sleeping sites and on control plots. 2 For the six selected species, a total of 1209 seedlings was recorded on the sleeping site plots, vs. 312 seedlings on the control plots. 3 On the sleeping site plots, seedlings of four species (V. michelii, M. guianensis, e. obovata and C. lucentifolium) showed clumped distributions. 4 Seed dispersal by red howler monkeys seems to induce heterogeneous distributions on both the large scale (seedlings of plant species dispersed by howler monkeys are concentrated under their sleeping sites) and the small scale (seedlings on sleeping site plots are distributed in clumps). 5 The survey clearly indicates the important role of howler monkeys as seed dispersers of these plant species. The aggregative pattern of seed dispersal by howlers could contribute to the floristic spatial heterogeneity of the primary tropical forest.