Hummingbird flower visitation rates vary with species traits, floral abundance and phenology across bioregions

A myriad of factors influence species interactions, and determining their relative importance is a major challenge in community ecology. Here, we explored the multiple factors influencing hummingbird visitation rates to flowers by considering pollinator and floral traits alongside the broader ecological context (i.e. phenology and floral abundance). Our data were collected from 32 systematically surveyed sites within native vegetation across three distinct Neotropical bioregions, each characterized by unique species composition and evolutionary histories. In total, we sampled 6423 flowering individuals, representing 404 plant species and 68 hummingbird species. At the community level, we found that hummingbirds primarily visit flowers with long, tubular corollas, aligning with predictions from pollination syndromes, and that visitation is also higher to flowers with straight corollas. At the species level, visitation frequency was associated with specific characteristics of the hummingbird species, such as its bill length and foraging behavior, where species often forage on flowers with matching morphological traits. Further, our findings extended beyond the expected trait preferences, revealing that visitation rates are also the outcome of the ecological context; particularly, the abundance of conspecific, but not heterospecific, flowers. The effect of conspecific abundance varied across bioregions, suggesting that from the plant perspective, intraspecific competition and facilitation could prevail in different regions. Additionally, we found that plant species whose floral morphology was more distinct from the other co-flowering species tended to attract more visits, but only if they were abundant enough to stand out within the floral community. These findings highlight how plant and pollinator traits, modulated by the ecological context, jointly shape pollination dynamics.