Plant and frugivore species characteristics drive frugivore contributions to seed dispersal effectiveness in a hyper-diverse community

Seed dispersal by frugivores is a crucial step of the life cycle of most
plants, influencing plant population and community dynamics. Although very
important for most ecosystems, we are just beginning to understand which
are the mechanisms driving frugivore-mediated seed dispersal. Most studies
identifying the drivers of seed dispersal use interaction frequency as a
proxy for estimating seed dispersal success, rather than looking at the
functional outcomes of those interactions (e.g., contributions to
successful seed germination). A valuable tool to link plant-frugivore
interactions to seed dispersal success is the seed dispersal effectiveness
(SDE) framework, which accounts for the quantity and quality components of
seed dispersal. We evaluated which mechanisms, including
morphological traits, trait matching, and phenological overlap of
interacting species, as well as the degree of frugivory and feeding
behavior of frugivores, influenced the quantity (interaction frequency and
number of seeds dispersed per visit) and quality (seed germination after
gut passage) components of SDE. To this end, we combined three methods
(focal observations, mist-netting, and camera traps) to sample
interactions between plants, birds, and mammals in a species-rich
community of Cerrado in southeastern Brazil. We recorded 590
pairwise interactions between 34 plants and 49 frugivores. We found that
phenological overlap among interacting species explained most of the
variation in interaction frequencies. Trait matching affected the number
of seeds dispersed per visit more for gulpers than mashers and peckers,
and frugivore body mass and seed sizes positively affected seed
germination. Finally, interaction frequencies had a stronger contribution
to SDE, compared to the number of seeds dispersed per visit and seed
germination, indicating an indirect effect of phenological overlap on
SDE. We found that highly abundant plant-frugivore species with
the most overlap in their phenologies also yield the highest values of
SDE, suggesting that phenological overlap was the most important driver of
SDE in our community. However, the number of seeds dispersed per visit
also influenced SDE and seed germination was species-specific, suggesting
that estimating SDE at the community level is necessary to understand how
communities work, and the current and future challenges they face.