CRITICAL POPULATION-SIZE FOR FIG WASP MUTUALISM IN A SEASONAL ENVIRONMENT - EFFECT AND EVOLUTION OF THE DURATION OF FEMALE RECEPTIVITY/

Fig trees and their pollinating wasps form ca. 750 pairs of obligate m utualists, mainly in the tropics. Survival of each partner depends on that of its associated species. Here, we examine the possible outcome of such an interaction at small population size. Using phenology data collected on Ficus natalensis in Gabon, we modelled wasp survival and the reproductive success of the trees according to the duration of rec eptivity of the tree, the amplitude of flowering seasonality, and the size of the fig tree population. Since the duration of receptivity is critical in these population level models, we also determined the infl uence of individual selection on this phenological trait. The models g ive three major results: (1) The minimum fig population size required to sustain a wasp population increases with the amplitude of seasonali ty, and decreases with increasing duration of receptivity; (2) tree po pulation reproductive success is higher when the duration of receptivi ty is longer and when the population is large, but (3) individual sele ction toward a long duration of receptivity is weak or absent.