Measuring the relative importance of different pollinators to plants

Abstract

THE development of a predictive theory of pollinator–plant coevolution requires a means of assessing and comparing quantitatively the costs and benefits of different pollinator foraging strategies and plant flowering strategies. Although there are quantitative data for pollinator strategies^1–3, the relative benefits to the plant of alternative pollinators, in terms of pollen transferred, ovules fertilised, and seeds set, have never been quantified for field conditions. Likewise, reference to the most effective pollinator⁴ of a plant species is often based on estimates of the abundance of alternative pollinators. Demonstrations that various pollinators can cause seed set in caged plants⁵ and that pollinators transfer pollen in different amounts^6,7 are difficult to relate to natural conditions. We have developed a quantitative approach for comparing the relative importance of alternative pollinators in terms of the quantity, level of out-crossing and efficiency of pollen transferred. We have used this approach to investigate the pollination of evening primroses, Oenothera fruticosa L. (Onagraceae), by two principal pollinators, European honey bees, Apis mellifera L., and soldier beetles, Chauliognathus marginatus Fab.