Network analysis has provided a comprehensive tool to understand the role of plant-pollinator interactions at the community level; however, most studies have analyzed this biotic interaction in terms of floral visitation and at specific times of the year. To understand how community-level interactions and phenology may influence floral evolution, it is important to assess how pollinators influence plant fitness on particular plant lineages throught the year. This is the first study that evaluates plant-pollinator networks, phenology and plant reproductive success on a group of coexisting congeners that exhibit different pollination syndromes including ornitophily, melitophily, sphingophily and chiropterophily. To evaluate the role of floral visitors on plant fitness, we conducted different network analyses of an Ipomoea community in the Pacific coast of Mexico, including: (1) all flower visitors, (2) visitors that contact the reproductive organs, (3) visitors that deposit pollen on stigmas, and (4) visitors that effect fruit and seed production. We conducted a series of pollination exclusion experiments to test the effectiveness of pollinators and determined the anthesis and flowering phenology of the Ipomoea species studied.
Results/Conclusions
Our study showed the following: (1) floral visitors of Ipomoea species included the pollinator functional group that corresponded to the floral syndrome as well as other visitors; (2) effective pollinators, in terms of pollen deposition on stigmas and fruit and seed production, corresponded to the floral syndromes and were the most frequent visitors in all cases; (3) secondary pollinators were also present in most syndromes; (4) coexisting Ipomoeas species sharing the same floral syndrome have staggered flowering phenology or different patterns of anthesis. In conclusion, the fitness network of plant-pollinators of Ipomoea is determined by the floral syndrome, providing strong support for Stebbins Principle that most frequent and effective floral visitors are the primary drivers of the evolution of floral traits. Furthermore, flowering phenology determines pollination network dynamics suggesting avoidance for competition in plants with the same pollination syndrome.