Individual flowering schedule, fruit set, and flower and seed predation in Vaccinium hirtum Thunb. (Ericaceae)

Flowering phenology is a trait that determines, in part, the reproductive success of plants. In this study, the variation in flowering schedule among individuals in four subpopulations of Vaccinium hirtum Thunb. (Ericaceae) and the effects of pollinators, flower predators, and predispersal seed predators on fruit production of individuals for 2 years were investigated. To describe variation in the flowering schedule among individuals, new methods for calculating two quantitative indices, rank order and degree of synchrony with others, are presented. The methods are suitable for quantifying between-individual differences in the synchronous schedule of a temperate spring-bloom species. The 2-year phenological census showed that there was variation in flowering schedule within local subpopulations. In all subpopulations, the flowering rank was retained for 2 years, and in two subpopulations, the relative synchrony of individuals was also retained. Correlation analysis between flowering schedule and fruit set suggested that early-flowering individuals were at a disadvantage regarding pollinator availability. However, weevil and fly larvae attacks often counteracted the disadvantage; later-flowering individuals were predated more intensively than early-flowering ones. The response of V. hirtum subpopulations to the selection pressure against early flowering may be disturbed by temporal and spatial variations in the influence of pollinators and predators.