Ecological context influences pollinator deterrence by alkaloids in floral nectar

Secondary compounds may benefit plants by deterring herbivores, but the presence of these defensive chemicals in floral nectar may also deter beneficial pollinators. This trade-off between sexual reproduction and defense has received minimal study. We determined whether the pollinator-deterring effects of a nectar alkaloid found in the perennial vine Gelsemium sempervirens depend on ecological context (i.e. the availability of alternative nectar sources) by monitoring the behavioural response of captive bumblebees (Bombus impatiens, an important pollinator of G. sempervirens in nature) to nectar alkaloids in several ecologically relevant scenarios. Although alkaloids in floral nectar tended to deter visitation by bumblebees, the magnitude of that effect depended greatly on the availability and nectar properties of alternative flowers. Ecological context should thus be considered when assessing ecological costs of plant defense in terms of pollination services. We consider adaptive strategies that would enable plants to minimize pollinator deterrence because of defensive compounds in flowers.