Functional generalism in plant–hummingbird interactions: Causes and consequences from a plant perspective

Plant species pollinated by animals differ in the pool of visitors they attract. Some attract functionally similar animals, while others engage with a broader set of functionally distinct visitors; we term this species-level variation functional generalism. Here, we explore the influence of plant traits and context-dependent factors on functional generalism, and the potential effects of this overlooked aspect of mutualistic interactions on species' reproductive outcomes. We quantified functional generalism in 211 hummingbird-visited plant species across 32 sites in three regions of Costa Rica, Ecuador and Brazil. We related functional generalism to plant traits (corolla length, opening, curvature) and context-dependent factors, including the abundance and flowering duration of the focal plant species, as well as the functional diversity of co-flowering plant species and of hummingbird pools during its flowering period. Finally, we assessed how functional generalism influenced plant reproductive outcomes (visitation rate and proportion of nectar-robbing visits). Species with long, narrow corollas had the highest functional generalism, attracting more functionally diverse hummingbirds. Functional generalism increased in functionally diverse plant communities, highlighting the influence of neighbours within the same trophic level. Abundant species with short flowering periods had greater functional generalism than less abundant, continuously flowering species. Functional generalism had a hump-shaped relationship with visitation rate, peaking at moderate levels but declining afterward. Moreover, the proportion of nectar-robbing visits increased with functional generalism. These findings reveal the joint influence of plant traits and community context on functional generalism, which in turn affects plants' reproductive success. Read the free Plain Language Summary for this article on the Journal blog.