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

Abstract

Summary1. 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). 2. 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 naïve bumblebees. 3. 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. 4. 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. 5. 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.

Carry-over effects of bumblebee associative learning in changing plant communities leads to increased costs of foraging

“…Experienced bumblebees learned novel information and progressively adapted their behaviour to the novel community composition, as indicated by the increasing number of visits to the rewarding inflorescences throughout the test phase. However, when the rewarding inflorescences resembled the deceptive inflorescences, bumblebees increasingly visited the deceptive inflorescences (Gumbert and Kunze 2001;Gigord et al 2002;Johnson et al 2003), despite the avoidance learning acquired during the training phase (see also Internicola et al 2007). By contrast, we found no significant difference in the number of deceptive inflorescences visited throughout the test phase when the rewarding inflorescences were of dissimilar colour (blue) to the deceptive inflorescences (yellow).…”

“…In particular, flower colour similarity between rewarding and deceptive plants slows down avoidance learning (Dyer and Chittka 2004a;Internicola et al 2007). As a result, bees usually visit more deceptive plants when they co-occur with rewarding species of similar rather than dissimilar flower colour (Gumbert and Kunze 2001;Gigord et al 2002;Johnson et al 2003;Internicola et al 2007). This suggests that the species composition of a plant community, and especially how rewards associate with floral cues, can affect bees' foraging choices and efficiency.…”

Bumble-bee learning selects for both early and long flowering in food-deceptive plants

“…Dissimilar signals should hasten the development of discrimination caused by both associative and avoidance learning [1,20]. Similarity of signals should slow the development of negative associations through associative learning with rewarding species, but should not alter the impact of avoidance learning.…”

“…Deceptive species compete poorly for pollinator services with rewarding species [1] because they provide no resources, which probably reduces their continued attraction of individual pollinators. Pollinator learning accentuates this limited competitiveness in two ways.…”

“…Additionally, the proportion of inexperienced pollinators should generally be higher early during the flowering season than later. All deceitful orchids are pollinated by insects with annual life cycles, so that in each flowering season all potential pollinators have a naive period before they learn which plant species are rewarding [1,20,21]. Flowering early when most pollinators are naive should expose GFD orchids to more frequent visits, even though more individuals of pollinating species are active later.…”