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

Abstract

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.

Coevolutionary Dynamics and the Conservation of Mutualisms

“…During this brief period, they must transit large distances in search of their single mutualist species. Simulation models indicate that fairly high numbers of trees must be present within their flight range to give them any chance of locating a flowering individual (Bronstein et al 1990;Anstett et al 1995Anstett et al , 1997b However, a number of very recent discoveries about this mutualism suggest that it exhibits more resilience than once thought:…”

Variation in Native Bee Faunas and its Implications for Detecting Community Changes

“…The increased attention to the role of mutualistic relationships in ecosystem function has led to questions of how floral visitors respond to habitat modifications resulting from human activity (Bronstein et al 1990, Banaszak 1995, Allen-Wardell et al 1998, Kremen and Ricketts 2000 and the introduction of exotic species (Thorp et al 1992). Many biologists believe the impact of human activities on native pollinators to be unrelentingly negative (Vinson et al 1993, Buchmann andNabhan 1996; but see Bohart 1972).…”

Phenology of tropical understory trees: patterns and correlates

“…Notable was the absence of high amongindividual asynchrony in annual (or sub-annual) patterns. Such patterns are characteristic of reproduction in tropical New World fig (Ficus) species (Milton et al 1982, Bronstein et al 1990 and is one of the factors that permits persistence of specialization of the fig pollination mutualism. Frugivores are rarely as specialized in their interactions with plants as are fig wasps, and the phenological patterns of these plant groups may reflects these differences.…”