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

1. 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. 2. 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). 3. 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 specialization, 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. 4. 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. 5. 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.