COS 95-6 - Pollination effectiveness of different floral visitors to Mimulus ringens

Background/Question/Methods

Reproduction for most flowering plants relies on mobile animals to move pollen among flowers. The pollination effectiveness of different visitors can vary widely, and depends on both the amount of pollen transferred during a single visit, and on pollinator visitation rate. Furthermore, some visitors may deplete floral rewards such as pollen and nectar without pollinating flowers, acting as pollen thieves or nectar robbers. This can reduce the proportion of pollen removed from anthers that is transported to receptive flowers. Such low efficiency visitors ‘waste’ pollen, and may therefore reduce a plant’s reproductive success through both male and female function.

Results/Conclusions

We used two different experimental approaches to measure the effectiveness of different visitor taxa for the perennial wetland plant Mimulus ringens. First, we compared the effectiveness of small solitary bees (primarily Halictidae), larger bees (primarily Bombus), and Hummingbirds in delivering to and removing pollen from flowers. Our results confirm larger bees are very effective visitors, and that small bees act primarily as pollen thieves, delivering little pollen. We also found that hummingbirds are not effective visitors. Second, we evaluated pollinator visitation and daily patterns in pollination and the standing crop of pollen and nectar at four sites. We found that abundance of the different pollinators differed strongly among sites and times, that the pollen-sensitive stigmas and closed by 10-11AM each day, and that pollen in anthers was exhausted by about the same time. Since small bees visit after 10-11AM, they are even less likely to be effective pollinators of M. ringens.