Kyoto, Japan -- If you were a bee, how would you choose a flower to land on? You might go to the most beautiful one, as pollination biologists have long suggested that flowers with striking colors attract pollinators more easily. Or perhaps, as other studies indicate, you might go where other bees are feeding, like seeing a long line outside a restaurant and thinking it must be worth the wait.
This raises the overlooked possibility of a floral "bandwagon effect": that even a less striking flower may attract as many pollinators as a brightly colored one, simply by securing early visitors. A team of researchers at Kyoto University was inspired to investigate this prospect and its implications.
"I began to wonder whether pollinators' use of social information might also influence plant reproductive success by shaping how plants attract and secure pollinators," says corresponding author Lina G Kawaguchi.
The researchers tested this idea by observing bumblebees in a large flight arena designed to resemble natural foraging conditions but with artificial flowers. They set one flower type to have declining resources, motivating the bees to shift to a newly blooming species. Bees encountered two fresh flower patches of different colors, with early arrivals present at only one patch, mimicked by placing dead bees on the flowers. Then the researchers used video and statistical analysis to determine how the presence of early visitors influenced the bees' decisions.
According to the analysis, the bees showed a strong color preference in the absence of early feeders. Yet the introduction of early arrivals resulted in a much different pattern. Bees frequently favored the patch with other bees, even when those flowers lacked a color advantage. When color preference and the presence of other bees conflicted, the two factors either cancelled each other out, or the bees showed a slight preference for following early arrivals.
These results indicate that flowers do not always need to be the most visually attractive to acquire pollinators, since bees rely on social information as much as -- or even more than -- their innate color preferences when choosing flowers for foraging. Instead, flowers that bloom slightly earlier and secure the first visitors may gain a lasting advantage, as those initial visits can trigger a cascade of subsequent visitors. This may represent an under-appreciated selective force shaping the evolution of floral traits.
"These findings suggest the possibility that the use of social information among pollinators can shape plants' interspecific competition for pollinators in nature," says Kawaguchi. "I believe this has important implications for future research on plant-pollinator interactions."
This study focused on a selected food source, but pollinators travel over large areas and can forage for weeks. Future work will require long-term field studies that track pollinators throughout the flowering season, including changes in behavior and competition among individuals. Such studies will illuminate how early pollinator acquisition ultimately contributes to plant reproductive success.
