Dynamic of seed dispersal by large frugivores in a forest-savanna mosaic subject to anthropic pressure in Western D.R. Congo

The Western Congolian forest-savanna mosaic is an ecotone subject to anthropogenic as well as natural fragmentation. Its forests have thus a considerable proportion of edges. This vegetation structure is likely to impact animal and plant communities and its dynamics such as animal mediated seed dispersal. Synergetically, activities such as bush meat hunting deplete large frugivores populations and thus decrease recruitment potential of the plants they disperse. Indeed, zoochory is known to be of great importance for tropical forests and a number of studies proved that large-seeded tree species closely depend on large frugivores for their regeneration. In such a context, we aim to understand how forest edges affect the dynamics of seed dispersal. More precisely, we wonder if the interactions between large seeds and their dispersers and predators are affected when closer to edges and how this can impact plant regeneration capacity. Also, we wonder if the dispersal and regeneration of large-seeded tree species depend on a few disproportionally important frugivores species. Bonobos, Pan paniscus, are among the largest frugivores left in the area and thus likely to be disproportionally important seed dispersers, though, their role as seed dispersers has yet been little investigated. We thus focus on the qualitative role for seed dispersal of the potentially keystone and umbrella ape species, the bonobo. To answer those questions, we study the main steps characteristics of large-seeded tree species regeneration process; namely quantitative seed dispersal, seed deposition pattern, germination capacity after transit in frugivore’s gut and, seed and seedling fate. By studying five different tree species at varying distances from forest edge, we aim to drive an inter-species comparison and to highlight the effect of forest edge on the regeneration process. We first quantify the seed production for each tree species and then evaluate the quantitative capacity of seed dispersal. By combining direct focal observations and camera trapping, we are able to highlight variations in composition of dispersers community and their respective contribution to seed dispersal. A literature review on each disperser species’ seed retention time and habitat use will allow the computation of the seed dispersal kernels. We will also evaluate the effect of seed ingestion by the bonobo on its germination capacity: seeds will be collected from dung to evaluate the effect of seed ingestion on the rate and velocity of germination. Finally, we will study the predation pressure exerted on dispersed and non-dispersed seeds and seedlings by setting up two sets of seeds below the canopy of parent trees and away from any conspecific trees. One set will be dispersed unprotected to seed predators; another one will be enclosed in a cage and permit seeds to germinate, allowing us to evaluate the herbivores pressure on seedlings.