On mutualists and exploiters: Plant-insect coevolution in pollinating seed-parasite systems

We investigate the coevolution of time of flowering and time of pollinator emergence in an obligate association between a plant and an insect that bot h pollinates and parasitizes flowers. Numerical analysis shows that the sys tem in general evolves towards a time of flowering different from the time favoured by the abiotic environment. The equilibrium towards which the syst em evolves is a local fitness maximum (an ESS) with respect to mutational v ariation in flowering time but, for the insect, it can be a local fitness m inimum at which selection on mutational variation in the time of insect eme rgence is disruptive. A consequence of evolutionary convergence to a fitnes s minimum is that pollinators having an earlier phenology can coexist with pollinators having a later phenology. Since late emerging insects are more likely to encounter and oviposit within previously pollinated flowers, thei r effect on the plant is more exploitative, leading them to function as che aters within the system. Thus, in the long term, pollinators and exploiters are likely to be found in stable coexistence in pollinating seed-parasite systems. (C) 2001 Academic Press.