“EXCESS” FLOWER PRODUCTION AND SELECTIVE FRUIT ABORTION: A MODEL OF POTENTIAL BENEFITS

Abstract

Flowering plants often produce more flowers than fruits. An initial “excess” of flowers, although making no numerical contribution to fruit set, may indirectly increase female reproductive success by allowing selective maturation of fruits of superior quality. I use a framework based on order statistics to assess the potential fitness benefit from this “wider choice” mechanism. The analysis shows that a floral surplus with subsequent selective abortion can generate large increases in mean female fitness. However, marginal fitness returns always diminished as the floral surplus increased (i.e., the fitness gain curve was always saturating), and imperfect selectivity of abortion could severely mute the advantages of surplus flowers. If the mating environment creates low variance in quality among developing fruits, then little benefit is derived from surplus flowers, while a high variance allows large fitness gains but with rapidly saturating benefits. The results imply that selection on flower number due to wider choice could be very strong in some circumstances, but that selection through this mechanism may often favor only a modest number of excess flowers.