Echinacea angustifolia, Narrow-leaved Purple Coneflower, serves as a model organism for long-lived, herbaceous, prairie forbs. E. angustifolia is self-incompatible and thus relies on insect pollinators for successful reproduction. The Echinacea Project has observed at least 26 species of insect pollinators visiting E. angustifolia, but some pollinators may be more effective than others. Previous studies have used rates of pollen deposition as a proxy for pollinator effectiveness. However, for Asteraceae members, the total amount of pollen deposited may not be as important as the pollinator’s ability to deposit pollen grains on multiple receptive stigmas. To test for pollinator effectiveness, we excluded pollinators and then observed a single pollinator visit. We used the number of styles shriveled per visit, a visual indication of compatible pollen receipt, as a quantitative measurement of pollinator effectiveness. We filmed all visits and used videos to quantify behavioral traits that might predict effectiveness, such as the number of times a pollinator circumnavigated the flowering head. Our objective for this study was to examine the effectiveness of single pollinator visits for the major insect taxa visiting E. angustifolia and assess if effectiveness could be explained by behavioral traits.
Results/Conclusions
During the four years of this study (2010, 2012, 2013 and 2014), we observed several hundred pollinator visits, 199 of which were included in our statistical analysis. Pollinator effectiveness varied among insect taxa and Andrena sp. were the most effective pollinators. Different pollinators circumnavigated the flowering head different numbers of times, but this behavior did not predict style shriveling. The two pollinators that circumnavigated the head the greatest number of times, Andrena sp. and female Melissodes bees, were also two of the largest and most effective pollinators. We conclude that the number of pollinator circumnavigations and body size may partially contribute to an insect’s effectiveness at pollinating E. angustifolia, but other traits not quantified in this study are also at play.