A controlled experiment with flowering plants and bumblebees found that pollinator abundance changes the balance between reaching potential mates and competition after pollen arrives. More bees increased potential mating opportunities without a detected increase in overall reproductive success. Tracking visits alongside seed parentage distinguished stages that genetic analysis alone can combine.
A peer-reviewed experiment with Brassica rapa, a flowering plant, and bumblebees found that pollinator abundance shifts the balance between successive stages of reproductive competition. Plants compete both to have pollen reach partners and, after pollination, to fertilize ovules. Changing bee numbers altered the relative importance of those stages in controlled populations, rather than establishing a single response for all flowering plants.[1], [2]
The Montpellier experiment placed ten plants in each of sixteen cages, with one, two or four bumblebees per population. Marked bees were observed visiting flowers for about half an hour. Visit sequences estimated potential mating partners; genetic analysis of seedlings identified actual parents. Parentage could be assigned to 1,099 of the 1,193 seedlings examined, separating an opportunity for pollen transfer from successful reproduction.[1]
More bees increased potential-mate numbers without detected increases in genetically identified mates, average pollen load or overall reproductive success. Much variation in male reproductive success arose after pollen deposition, during fertilization. Scarce pollinators increased inequality in access to potential mates. The short visits, cages and single commercial plant line limit extrapolation to natural populations, where pollinator movements and growing conditions can differ.[1]
