Plant and frugivore species characteristics drive frugivore contributions to seed dispersal effectiveness in a hyperdiverse community

Abstract

1. 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.2. We evaluated which mechanisms, including morphological traits, trait matching and phenological overlap of interacting species, as well as degree of frugivory and feeding behaviour 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.3. 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 with the number of seeds dispersed per visit and seed germination, indicating an indirect effect of phenological overlap on SDE.4. Synthesis. 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 this hyperdiverse 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.