Relationships between flowering phenology, plant size, and female reproductive output in a dioecious shrub, Ilex leucoclada (Aquifoliaceae)

Abstract

Flowering phenology is critical for reproduction in dioecious species, but selection on timing of flowering may be weakened by physiological factors such as plant size, and external factors such as climate. We investigated the flowering phenology of male and female adults, and female reproductive output, in 10 patches with various sex ratios, of the dioecious shrub Ilex leucoclada (Maxim.) Makino over three consecutive years in an old-growth beech forest. Sexual dimorphism was observed in flowering amplitude, but not in other traits examined, including flowering onset date, duration, peak date, and synchrony with plants of the opposite sex in the population. Plant size had a consistent, positive effect on flowering amplitude in both sexes throughout the study period, but its effects on other factors, including the extent of fruit set, varied. Females in mixed patches showed higher fruit set than those in female patches. Furthermore, although the reproductive output of the female I. leucoclada plants is likely to be affected by flowering phenological traits in the mixed patches, the importance of these factor is probably modulated by other variables, including precipitation (which had a major effect on male flowering patterns) and the spatial distribution of the males.