Competition for pollinator visitation between deceptive and rewarding artificial inflorescences: an experimental test of the effects of floral colour similarity and spatial mingling

While many plant species offer rewards (e.g. nectar) to pollinators, some species, particularly in orchids, do not provide rewards. Ecological factors, such as interactions with rewarding co-flowering species may affect pollinator visitation rates to such deceptive species by influencing pollinator ability to learn to avoid deceptive plants (avoidance learning). We tested the effect of flower colour similarity (similar vs dissimilar) and fine-scale spatial mingling (monospecific vs heterospecific patches) of rewarding and deceptive artificial plants on pollinator visitation in a fully crossed design. We also examined the effect of these factors on learning of initially naive bumblebees. Over time, bumblebees increasingly avoided the deceptive plants, but at a significantly faster rate when deceptive and rewarding plants had dissimilar flower colours than when they were similar. Deceptive plants received more visits when mingled in heterospecific patches with rewarding plants of similar flower colour than when mingled with dissimilar ones. This difference was not significant when rewarding and deceptive plants were spatially separated in monospecific patches. In conclusion, both spatial mingling and flower colour similarity affected pollinator visitation to and avoidance learning of deceptive plants. This proves the validity of artificial experimental systems to study the isolated and joint effect of plant traits, and ecological factors that are crucial for the maintenance of deceptive species in natural populations.