The Effect of the Dispersion of Non-rewarding Flowers on Pollination by Bumblebees (Bombus impatiens): A Lab Study

The vast majority of plant species rely on insect pollination for sexual reproduction, and most plant species offer rewards like nectar to their pollinators. However, several taxa, including several thousand species of orchids, are “non-rewarding” and offer no reward to their pollinators, and it is of interest how these species are able to attract and compete for visits from pollinators. It has been found that the density and dispersion of non-rewarding plant species among rewarding species can have an effect on pollinator visitation, learning, and constancy, and successful pollen transfer. The current study aimed to see the effect of two dispersion patterns of non-rewarding flowers on both the quantity of visits from pollinators and the rate of switching of pollinators (i.e. quality of visits) to test which distribution would be most beneficial for non-rewarding flowers to grow. 46 individual bumble bees (Bombus impatiens) were tested in a two-part lab study with two artificial flower colors (blue-rewarding, purple-unrewarding) and two flower distributions (homogeneous clumps vs intermixed). I collected and analyzed data on the number of visits to each color, switches between colors, and consecutive visits to the same color. I discovered that the intermixed distribution produced the highest number of visits to the non-rewarding flowers, but also had a significantly greater rate of switching between flower species, which could result in higher interspecific pollen transfer (IPT) in nature. The aggregate distribution caused the most direct flights to flowers of the same type. These results indicate that while the intermixed distribution may have caused a higher quantity of visits to non-rewarding flowers, the aggregate distribution produced higher quality visits. Further research should be done with live plants to test the effect of these results on reproductive output to see if quantity or quality of visits is more important