Threatened species are disproportionately important interactors in a seed dispersal network in Southeast Asia

Southeast Asia is a conservation priority region due to its high biodiversity—including megafauna—and high rates of defaunation, which has negative impacts on key ecological processes such as seed dispersal. Yet, seed dispersal interactions at the community level have rarely been described in this region. This is a major knowledge gap because medium-size and large animals are disproportionately affected by defaunation and they also have critical roles as seed dispersers. Hence, community-wide studies that encompass a full range of animal body sizes across diverse regions are required, to enable an improved understanding of defaunation impacts. Here, we (a) describe a highly diverse Southeast Asian seed dispersal network (Khao Yai National Park, Thailand), (b) assess the role of body size in identifying important animals and (c) determine if threatened species are disproportionately important in the network. The network is highly nested and modular, with species phylogeny, body size and seed size having a major influence on modularity; mammals and birds occupied different modules. Generalist species playing important roles in the network were mainly medium or large-sized. However, the largest disperser (elephants) played a relatively minor role in seed dispersal in this community, and bulbuls were important despite their small size. Many threatened animal species were important within the network as connector species and through their interactions with a larger number of plant species. Consequently, the resilience of this biodiversity hotspot is at threat by the potential nonrandom loss of the most important seed dispersers.