Data from: The cryptic regulation of diversity by functionally complementary large tropical forest herbivores

1. Tropical forests hold some of the world’s most diverse communities of
plants. Many populations of large-bodied herbivores are threatened in
these systems, yet their ecological functions and contribution towards the
maintenance of high levels of plant diversity are poorly known. The impact
of these herbivores on plant communities through antagonistic seed and
seedling predation has received much attention, whilst their relevance as
seed dispersal agents has been largely overlooked in experimental studies.
2. Here we tested how two key and functionally distinct large generalist
mammalian herbivore species (the tapir Tapirus terrestris- a solitary
browser and generalist seed disperser, and the white-lipped peccary
Tayassu pecari- a group-living generalist seed/seedling predator) affect
spatiotemporal patterns of diversity of seedling communities in tropical
forests. We conducted a long-term multi-region landscape-scale exclusion
experiment across four regions of the Atlantic forest of Brazil,
representing a functional gradient of defaunation where these species were
either present and absent in isolation and in combination. 3. Our results
indicate that mammalian herbivores have a substantial role in regulating
beta diversity in space and time. Seedling recruitment was strongly
limited by the presence of the seed/seedling predator species (the
peccary), but the presence of the browser and seed disperser (the tapir)
had null net effects. Alpha diversity of seedlings at the community level
did not respond to large herbivore exclusion at any region, whereas beta
diversity decreased only where both herbivores were simultaneously
excluded. Surprisingly, the synergic positive effect of both herbivore
types on beta diversity was linked to increased evenness amongst dominant
plant species, and a simultaneous decrease in alpha diversity of rare
species. 4. Synthesis: Together, these results challenge the common
perception that large tropical forest herbivores maintain tropical forest
diversity through antagonistic interactions, suggesting instead a
synergistic effect of antagonistic predation and mutualistic seed
dispersal on regional compositional diversity and local community
assembly. We suggest that the defaunation of large-bodied herbivores with
complementary functions strongly affects the structure and dynamics of
plant communities through cryptic mechanisms that remain largely
unexplored.