The ability to disperse large seeds, rather than body mass alone, defines the importance of animals in a hyper-diverse seed dispersal network

Large-bodied animals play irreplaceable roles in seed dispersal, partly due to their capacity to disperse large seeds. Understanding this role at a community level has been limited by the paucity of network studies that include large vertebrates, and the almost complete absence of studies including synzoochoric dispersers. Synzoochoric dispersers can disperse seeds disproportionately large for their body size, potentially overlapping the roles of large-bodied animals. A comprehensive network, inclusive of large vertebrates and synzoochorous dispersers, is imperative to understand seed dispersal at a community level. Here, we analysed the seed dispersal network of a hyper-diverse Sundaic forest in Malaysia using local ecological knowledge and including multiple forms of endozoochorous and synzoochorous dispersal. We evaluated the extent to which three disperser traits: body mass, seed-handling ability (size of the largest seed dispersed) and diet explained the importance of animals in the network. We evaluated dispersers' relative importance using four network metrics-degree of specialisation (nested rank), species strength, within-module connectivity (z-value) and between-modules connectivity (c-value). We found that seed-handling ability had the biggest effect on a disperser's importance, with strong effects on three network metrics (species strength, ecological specialisation and z-value) and moderate effects on connectivity between modules. Body mass was important in defining interactions within modules, and dietary differences defined the ecological specialisation of species in seed dispersal. Important dispersers in our network were large-seed dispersers (e.g. rats, gibbons), large-bodied animals, in particular the Asian elephant, and animals with frugivorous diets such as hornbills. Synthesis. Our work uncovers the significance of seed-handling ability in identifying pivotal seed dispersal roles in tropical rainforests. Key dispersers include large-bodied herbivores and medium-sized frugivores that could disperse large seeds by endozoochory, and smaller rodents that dispersed similar-sized seeds by synzoochory. Many of the species that emerged as particularly important for the seed dispersal network are currently threatened (e.g. the Asian elephant, gibbons and hornbills). Their protection or reintroduction should be a top conservation priority.

Automated summary

Large-bodied animals play crucial roles in seed dispersal, with synzoochoric dispersers potentially overlapping the roles of large vertebrates. Seed-handling ability is key in identifying pivotal seed dispersers in tropical rainforests, with large herbivores and frugivores being important in the seed dispersal network. Protecting threatened species such as the Asian elephant, gibbons, and hornbills is essential for maintaining the integrity of seed dispersal networks.