Floral Roles in Hummingbirds-Mediated Indirect Plant Interactions in Tropical Andean Communities

In pollination networks, indirect plant–plant interactions mediated by their shared pollinators can shape community dynamics and species fitness; yet, the influence of floral traits on species roles remains unclear, particularly in diverse ecosystems like the tropical Andes. We studied hummingbird-mediated interactions among 31 flowering plants in three high-elevation shrubby habitats located in southern Ecuador. During August and November 2022, and January 2023, we collected stigma samples and constructed weighted interaction networks linked by heterospecific pollen grains. Species roles were determined by defining if they were donors or receivers of pollen, measured by node degree out and node degree in, respectively. We also explored the association between the abundance of flowers and different floral traits and species roles. Finally, we assessed the potential influence of floral roles on species fitness by calculating the ratio of conspecific-to-heterospecific pollen grains observed in each species. We found that the identity of donor and receiver species was highly dynamic across habitats and time. Receiver species were characterized by being highly abundant, while donor species presented high levels of nectar production. Receiver species received more heterospecific pollen than conspecific pollen, indicating that the pollen-sharing roles of species could have fitness consequences. Our findings highlight the importance of some floral traits and abundance in shaping floral roles and their potential fitness consequences in hummingbird-mediated indirect interactions.