Disrupted dispersal in logged tropical forest

Selective logging in tropical forests is restricted to a few species, the so-called commercial species. Among those commercial species, many produce fleshy fruits of large size. These tree species provide food to a large number of mammals and birds that often exclusively rely on these resources. These mammals and birds may also be vital for the demography of fleshy fruit trees because they act as dispersers towards more suitable place for seedling establishment (directed dispersal hypothesis or colonization hypothesis), or they increase seedling survival by avoiding conspecific high densities (escape hypothesis). Selective logging generally targets large trees, above the legal minimum cutting diameter, that also produce an important quantity of fruits to frugivores feeding in the canopy. Therefore, selective logging may impact frugivore populations in the long-term and in fine may disrupt the dispersal processes of logged species but not only. Indeed, selective logging of the largest - in terms of size and quantity -fleshy fruit producers may impact all fleshy fruit producers in decreasing the abundance of the resources hence creating local extinction of frugivores (the resource concentration hypothesis). Large frugivores feeding on the largest fruits may be more rapidly impacted. Until now studying the effect of logging is not an easy task because logging is generally correlated to hunting pressure. Based on a multispecies comparison using data from a replicated experimental logged forest with various intensities (and including control plots) at constant hunting pressure, we test the effect of selective logging on seed dispersal of tropical forest trees. Seed dispersal will be estimated as a cluster size using Ripley's K functions. In particular, we will test if dispersal distances of fleshy fruit species in logged plots decrease compared to control plots. We hypothesize that animal-dispersed species with larger seeds are dispersed less far away in treated vs control plots than smaller seeded and non animal-dispersed species. We propose to take into account tree species with different dispersal syndromes i.e. tree species with different seed size among animal-dispersed trees, and tree species with different dispersal mode such as wind-dispersed, mechanically dispersed trees or gravity dispersed trees. We also propose to link the difference in dispersal between disturbed and undisturbed forest with the structural properties of the interaction network. (Texte intégral)