The effects of primary and secondary nectar robbing of Ipomopsis aggregata on hummingbird visitation.

Abstract

Nectar robbers feed on the nectar obtained through holes that have been chewed into the flower. This behavior often leads to a reduction in effective pollination because nectar robbers avoid floral reproductive structures (Inouye 1980). Primary nectar robbers puncture the flower, creating an opening in the petal from which to remove nectar, while secondary nectar robbers use the holes created by primary robbers. Studies have shown that nectar robbing can negatively affect plant reproduction by deterring legitimate pollinators (Irwin et al. 2010). Furthermore, data have shown that secondary nectar robbing can result in increased reproduction costs beyond that caused by primary robbing alone (Richman et al. in prep). One reason this might be is that legitimate pollinators are further deterred as plants incur more nectar robbing. I have tested this hypothesis by collecting 30 Ipomopsis aggregata plants and subjecting them to varying levels of nectar robbing: none, primary robbing only, and secondary robbing. After applying treatments I arranged them in a field and observed hummingbird visitations, recording the sex and species of the bird as well as the specific plants visited and the number of flowers probed per plant. The data show that hummingbirds probed more flowers per plant of the control group than they did of either of the nectar robbed groups and they probed more flowers per plant of the primary group than they did of the secondary group. This suggests that hummingbirds will not stay at a plant as long if it has a smaller nectar reward.

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