Flowering overlap and floral trait similarity help explain the structure of pollination networks

Co-flowering communities are usually characterized by high plant generalization but knowledge of the underlying factors leading to high levels of generalization and pollinator sharing, and how these may contribute to network structure is still limited. Flowering phenology and floral trait similarity are considered among the most important factors determining plant generalization and pollinator sharing. However, these have been evaluated independently even though they can act in concert with each other. Moreover, the importance of flowering phenology and floral similarity, via their effects on plant generalization, in the structure of plant-pollinator networks has been scarcely studied. Here, we aim to evaluate the effect of flowering phenology and floral similarity in mediating the degree of pollinator sharing and plant generalization in two coastal communities and uncover their importance as drivers of plant-pollinator network structure. We recorded flower production per species, as well as the identity and frequency of floral visitors along the entire flowering season. We estimated the degree of flowering overlap, the degree of floral similarity (using floral traits associated with size and colour) and the degree of pollinator sharing among plant species within both communities. Structural equation models (SEM) showed a positive effect of flowering overlap on pollinator sharing and plant generalization. Pollinator sharing and plant generalization positively affected network nestedness. Furthermore, SEM showed a direct positive effect of flowering overlap on network modularity. The SEM analyses also revealed a significant interaction effect of floral similarity and flowering overlap on pollinator sharing, with consequences for network nestedness in one community.

Automated summary

Co-flowering communities with high plant generalization and pollinator sharing are influenced by flowering phenology and floral similarity, which play important roles in shaping plant-pollinator network structure. Flowering overlap has a positive effect on pollinator sharing and plant generalization, and also influences network nestedness and modularity. The interaction between floral similarity and flowering overlap affects pollinator sharing and network nestedness.