PMC

The number of insect visitors (A) and the number of flowers visited (B) in artificial arrays of inflorescences of staminate-phase vs. pink pistillate-phase flowers and arrays of staminate-phase vs. pale pistillate-phase flowers in 2012. In 2013, the number of insect visitors (C) and the number of flowers visited (D) was recorded for 3 types of arrays: staminate-phase vs. pink pistillate-phase flowers, staminate-phase vs. pale pistillate-phase flowers, and pale pistillate-phase vs. pink pistillate-phase flowers. An asterisk (*) indicates a comparison that is statistically different (α = 0.05).

A: The time spent foraging within the cluster by individual honeybees increased with the number of flowers available. B: The number of flowers visited increased with the total number of flowers available. C: The proportion of flowers visited by individual bees decreased with the number of flowers available. D: The number of flowers exploited per minute did not show any significant relationship to the number of flowers available. X-axis in A.—D. and y-axis in A. and B. are on a log-scale.

Each panel represents one possible outcome. If red flowers predominate (left), bees forage at blue and red flowers, while all birds forage at red flowers. If blue and red flowers are equally abundant (middle), there is complete resource partitioning, with bees foraging at blue flowers and birds at red flowers. If blue flowers become more abundant (right), all bees forage at blue flowers, while birds forage at red and blue flowers.

Conceptual diagram showing whether the behavioral rules when pollinators choose flowers to be visited leads to sexual dimorphism. In the simulations, each flower has a different size and nectar amount. As an example, we illustrate above yellow and orange flowers to show relatively large flowers without nectar, and relatively small flowers with nectar, respectively (yellow and orange do not show differences in floral color). Red in the center of orange flowers shows nectar reward and open circles in the center of yellow flowers show no nectar reward. Flowers and flies are drawn by K. Tsuji and Y. Kanzaki, respectively. The left: random model assumes that pollinators decide flowers randomly without recognition of flower size and nectar amount. Under the no selective pressure on floral size and nectar amount, no evolution of sexual difference is predicted. The middle: size-dependent model assumes that pollinators decide flowers based on floral size. In this model, since female-female and male-male competitions occur, large flowers are evolved, but sexual difference is not evolved. The right: experience model assumes that naïve pollinators will decide flowers based on flower size, and experienced pollinators choose flowers based on the nectar reward of their previous visited flower. For example, if a naïve pollinator visits the largest flower without nectar at first, the pollinator next chooses flower with a different size (i.e., smaller flower than the largest one) and avoids visiting such large flower without nectar. This pollinator behavior drives the evolution of sexual differences in floral traits: in male flowers, large flowers are evolved to attract naïve pollinators and less nectar reward to make experienced pollinators with pollen avoid the flowers with the same sizes as the male itself, while in female flowers, flowers with different size from male flowers are evolved to attract pollinators that has already visited nectar less male flowers.