Trait patterns across space and time suggest an interplay of facilitation and competition acting on Neotropical hummingbird-pollinated plant communities

Pollinators may influence plant community assembly through biotic filtering and/or plant-plant competition and facilitation. The relative importance of each process, however, vary according to the scale and how strongly plants share their pollinators, and possibly in relation to the pollinator groups considered. We here investigated the assembly of three Atlantic forest hummingbird-pollinated plant communities across space (among all species in the communities) and time, i.e. yearly flowering phenology (between pairs of co-flowering species), based on the pairwise distances of multiple floral traits (corolla length, anther and stigma height, colour and nectar). Because tropical hummingbird-pollinated plants are often subdivided in two pollination niches (hermits versus non-hermits), we also analyzed these groups separately. We found that trait structure across space was clustered for some floral traits, suggesting biotic filtering and facilitation. All floral traits had weak phylogenetic signal, indicating that closely related species were not more similar than distantly related species. Moreover, floral traits were randomly structured along the phenology when analyzing all plants together. On the other hand, we found similar corolla length but divergent anther height in co-flowering pairs within the same pollination niche. Thus, plants may benefit from flowering together and avoid competition through fine adjustments in reproductive traits. The results also suggest that clear signals of competition and facilitation among plants are only apparent when species strongly share their pollinators and depending on the traits that are considered. Our study illustrates a complex interplay of biotic filtering, facilitation and competition as processes structuring guilds of plants sharing the same functional group of pollinators.