Effects of pollinators and flower bud herbivores on reproductive success of two ericaceous woody species differing in flowering season

Abstract

To investigate the relative importance of pollinators and flower bud herbivores on final fruit set, the ratios of flower to flower bud (flower/bud), fruit to flower (fruit/flower), and fruit to flower bud (fruit/bud) were examined for the two bumble-bee-pollinated ericaceous species that have different flowering seasons: Pieris japonica (Thunb.) D. Don produces flower buds in autumn and blooms in early spring, whereas Lyonia ovalifolia (Wall.) Drude produces flower buds and blooms in late spring. Floral longevity was longer in P. japonica than in L. ovalifolia, and bagged flowers had an even longer floral longevity. The fruit/flower ratio was similar between the cross-pollinated and control flowers in P. japonica, but was smaller in control flowers than in cross-pollinated flowers in L. ovalifolia. Despite unpredictable pollinator activity in early spring, long flowering duration and no competition for pollinators facilitated reproductive success of P. japonica. In contrast, short flowering duration and severe competition for pollinators limited the reproductive success of L. ovalifolia. Flower bud herbivory was more severe in P. japonica than in L. ovalifolia. In both species, predispersal seed herbivores were negligible. Consequently, the fruit/bud ratio was mainly affected by the flower/bud ratio in P. japonica and by the fruit/flower ratio in L. ovalifolia. Our results suggest that despite intense herbivory of flower buds, early spring flowering of P. japonica facilitates pollination because of less competition for pollinators in comparison to L. ovalifolia. Thus, the relative importance of pollinators and herbivores on fruit set differs between the two studied species that differ in flowering periods.