Variation in rate of nectar production depends on floral display size: a pollinator manipulation hypothesis

1. Pollinators typically visit more flowers on plants with larger floral displays, which should present such attractive plants with significant pollen transport losses. 2. Many-flowered plants with hermaphrodite flowers might reduce the costs of attractiveness by encouraging fewer sequential flower visits by pollinators. One mechanism that accomplishes this is to produce variable nectar rewards, which will cause risk-averse foragers to leave the plant after visiting fewer flowers. 3. We test the prediction that within-plant variability in nectar production rate increases with the relative number of open flowers on a plant. A field survey of nine herbaceous angiosperm species native to Alberta, Canada revealed a significant positive correlation between nectar variability (measured as standard deviation) and the size of the floral display within species. This relationship existed over and above the null expectation of a positive correlation between mean and SD. 4. Our results suggest that multiflowered plants might maximize the male fitness returns associated with a plant's attraction status (determined by relative display size), by taking advantage of risk-averse foraging by their pollinators.