Increase in ant density promotes dual effects on bee behaviour and plant reproductive performance

Floral rewards do not only attract pollinators, but also herbivores and their predators. Ants are attracted by extrafloral nectaries (EFNs), situated near flowers, and may interfere with the efficiency and behaviour of pollinators. We tested the hypothesis that the impacts of ant–pollinator interactions in plant–pollinator systems are dependent on (1) the seasonal activity of EFNs, which increase ant abundance closer to flowers; (2) consequently, an ant effect, where ants decrease the temporal niche overlap of bees due to predator avoidance; and (3) ant density, where higher densities may negatively affect plant–pollinator interactions and plant performance. We studied two ant–plant–pollinator systems based on Banisteriopsis campestris and Banisteriopsis malifolia plant species. The periods of high ant abundance coincided with plant species blooming. The presence of ants around flowers reduced the visitation rates of the smaller bees and the temporal niche overlap between bee species was not higher than randomly expected when ants had free access. Additionally, we observed variable ant effects on fruit set and duration of bee visits to both Malpighiaceae species when ant density was experimentally kept constant on branches, especially on B. campestris. Our goal was to show the dual role of ant density effects, especially because the different outcomes are not commonly observed in the same plant species. We believe that reduced temporal niche overlap between floral visitors due to ant presence provides an opportunity for smaller bees to improve compatible pollination behaviour. Additionally, we concluded that ant density had variable effects on floral visitor behaviours and plant reproductive performance.