Flower visitor networks: Reduced reproductive success driven by antagonists in a hummingbird-pollinated species

Abstract

Flower–animal interactions encompass a continuum of mutualistic to antagonistic behaviors. Although the importance of pollinators in interaction networks has been widely reported, the role of floral antagonists remains overlooked. In Collaea cipoensis, an endemic shrub from southeastern Brazil, we modeled an individual-based network assessing the flower visitors' functional behavior and tested if plant centrality increases fitness. Centrality indicates how well-connected a given plant is with the rest of the conspecifics through shared flower visitors. Specifically, we tested if flower visitor interactions are amplified by many-flowered individuals, and whether the relationship between centrality and plant fitness encompasses the effects of mutualists or antagonists. Subsequently, we quantified each visiting species' effectiveness. Antagonistic interactions were the most frequent in the network (97% of visits), primarily conducted by the nectar-robbing bee Trigona spinipes (66%), which was also the most central species and detrimental antagonist. The hummingbirds Colibri serrirostris and Eupatomena macroura were the most efficient pollinators, with a high contribution to the quantity—floral visitation—and the quality—viable seeds—components, respectively. Many-flowered plants showed greater centrality, which boosted the plant's cohesion in the network and increased flower visitation. Accordingly, many-flowered plants were better connected, mainly due to antagonistic visitors. Thus, centrality increases were not positively translated into more reproductive success. Our results reinforce the dynamic scenarios of flower–animal interactions, with consequences to plant reproductive ecology. We highlight the importance of incorporating distinct types of interactions to unveil the complexity of interacting systems, that when not explored, hide potential evolutionary consequences for plant reproductive success. Abstract in Portuguese is available with online material.