Columbine pollination success not determined by a proteinaceous reward to hummingbird pollinators

Abstract

Plants provision pollinators with a variety of nutritious or otherwise beneficial rewards. Hummingbirds (primarily Calypte anna) pollinate the columbine Aquilegia eximia. In addition to drinking nectar, they glean entrapped insects from its sticky surfaces. To test the hypothesis that this insect carrion, an abundant and easily-collected protein source, serves as a provision to the pollinator and increases pollination I experimentally manipulated this reward and measured pollination success. I set up three treatments - an insect carrion addition, carrion removal, and an unmanipulated control - on small patches of the plant in each of five populations of A. eximia. Pollination success, measured by seed set in emasculated flowers, was unaffected by carrion level. Pollination success positively correlated with average floral display in each patch; this suggests that local nectar reward in an area is more important than this proteinaceous reward in determining pollination success. Stickiness in this system may function as an effective exclusion mechanism for smaller-bodied pollinators. While this study did not demonstrate that captured insects increased reproductive success of this columbine, this interaction (and pollinator exclusion) may play a role in other hummingbird-plant interactions, as hummingbird pollination and insect-entrapment occur together in at least nine species of six plant families.