Fungi, insects, and mammals differentially impact the diversity of
tropical tree seedling communities
Abstract
Natural enemies have been implicated as agents of negative density
dependence (NDD) in tropical forests, but their relative contributions
to NDD and thus the maintenance of diversity are largely unknown. We
assessed the influence of natural enemies on density-dependent
interactions among tropical seedlings, monitoring survival and relative
growth rates in plots that excluded fungal pathogens, insects, small
mammals, or large mammals. Only fungal pathogens caused density
dependent mortality, and their exclusion reduced species diversity.
Insects reduced relative growth rates when stem density was high, but
because this was not driven by conspecific density, insects had little
effect on species diversity. Mammals did not cause NDD interactions. We
conclude that both fungal pathogens and insects drive NDD interactions
among seedlings. Even so, only fungal pathogens increased species
diversity, and consequently contribute critically to the structure of
tropical tree communities.