The Ecological Consequences of Flowering Asynchrony in Monoecious Figs: A Simulation Study

For plants with temporally separate sexual phases to outcross, population-level flowering asynchrony is necessary, but this can decrease the resource base available for pollinators. We developed a simulation model to examine the consequences of such asynchrony for individual reproductive success and long-term pollinator maintenance within monoecious fig populations. In figs, flowering is synchronous within a tree and the specialist pollinators/seed predators can only survive briefly away from trees. Consequently, population-level flowering asynchrony must extend year-round for pollinators to persist locally. In repeated stochastic simulations using phenological traits of one well-studied species (Ficus natalensis), a median of 95 trees was required to produce an asynchronous sequence that could maintain local pollinator populations for 4 yr. However, many trees in those simulated populations were either male-sterile (10%) or both male- and female-sterile (35%), because their sexual phases were not well timed with the opposite phases of other trees. Sterility within a population approached zero at 2-3 times the critical population size. Both the predicted critical population size and frequency of success of the trees within it depended strongly on the duration of reproductive episodes and the intervals between episodes. The level of within-tree reproductive synchrony was also critical: doubling the length of time over which individuals could donate pollen resulted in a 39% decrease in critical population size and a 27% increased likelihood that individuals would achieve at least some reproductive success. These results point to the need for precise phenological data for estimating plant fitness and population structure both in models and in the field.