Co-flowering neighbors influence the ecological specialization on pollinators of plant species

The generalization-specialization gradient exhibited in pollination interactions is currently receiving much attention. Although the ecological specialization on pollinators is usually considered as a plant species property, it is well-known that pollinators visiting a particular plant species can differ between localities. However, the role that co-flowering species play on the composition of pollinator visits to particular plant species has rarely been considered. We investigated this role using field observations on pollinator visits to six plant species within two communities. We related the variation in the generalization level and the composition of visits to these species to variables describing the co-flowering neighborhood. The diversity, identity and density of the co-flowering species affected both the level of generalization on pollinators and the identity of the visitors of particular plant species. Although the responses to co-flowering neighborhood were highly species-specific, the generalization level and the visits by uncommon pollinators generally increased with the total number of flowers and plant diversity. In very specialized plant species, the visits by the main pollinators were not affected by the co-flowering neighborhood. In more generalized plant species, however, the visits by the main pollinators increased with an increase in the density of flowers, either of the focal species or of the pollinator-sharing species. Our results have two important implications: (1) variations in the interactions with the pollination context may provide high stability to plant communities, and (2) evolution of flower and pollinator traits may depend on the co-flowering community.