Pollinators maintain biodiversity in assembling plant communities

Most angiosperms are animal-pollinated, and animal pollination increases fitness in many plant species. Although it is less well-studied than other factors, plant biodiversity may be maintained by pollinators and the associated seedling recruitment that occurs after fertilization. We experimentally applied three levels of pollinator visitation to all forb flowers that emerged in patches of a prairie restoration with different graminoid/forb ratio seed mixes: (1) a pollinator exclusion treatment where flowers were bagged, (2) an augmented pollination treatment where flowers were hand-pollinated, and (3) a control that was untreated. Plant diversity was estimated in the fourth growing season. Pollinator exclusion led to a 50% reduction of viable seeds in animal-pollinated species, a 27% decline in animal-pollinated species richness, and a 23% decline in plant species richness overall. Pollinator exclusion also eliminated the positive relationship between forb abundance and plant richness observed in controls and augmented pollination treatments. Overall, our results suggest that pollinator decline in human-impacted environments may be leading to a plant-pollinator extinction vortex in which reduced pollination leads to reductions in local plant diversity, subsequent declines in pollinators, and further reductions in plant diversity. This suggests that plant biodiversity at the community level can be limited by animal pollinators.