Figure 1.

Number of fertilization events in a dioecious population, as a function of the sequence in which pollinators visit female (f) and male (m) plants. In this example, V=3 plants visited per pollinator foraging trip, which can result in either zero, one or two female plants being fertilized. The average number of pollen delivery events for this particular example is [x] [4(0)+3(1)+1(2)]/8=0.625x, where x is the advantage females experience over hermaphrodites (e.g. due to reduced inbreeding depression). Setting x to 2 (as in figure 2), then an average of 1.25 female plants are fertilized when pollinators visit three plants per trip. In contrast, all such trips in a hermaphroditic population fertilize two plants, producing a 2/1.25=1.6×advantage to hermaphroditism.