Flowering and seasonal changes in flower sex ratio and frequency of flower visitors in a population of Saxifraga hirculus

Abstract

The open, dish‐shaped flowers ofSaxifraga hirculusreflected ultraviolet and yellow light, contained very small amounts of nectar, and contained an average of about 75300 pollen grains per flower. Almost 11% of the pollen was inviable. Stigmatic pollen loads and seed set decreased during the course of the season. The plant appeared to be fully between‐ramet compatible and partially within‐ramet compatible. Seed set for the population was 30.3%. The protandrous flower opened during the day and had male and female phases of nine and three days, respectively. The protandrous system reduced the number of pollination days by a third.At least 26 species of insects, 16 of which were syrphids, visited the flowers. Based on the number of flower visits, four species were the dominant visitors ofS. hirculus: Eurimyia lineataandNeoascia tenur(Diptera: Syrphidae);Asindulum nigrum(Diptera: Mycetophilidae), andZygaena trlfolii(Lepidoptera: Zygaenidae).Eurimyia lineatawas the most frequent visitor (51% of all visits). As the season advanced, the visits byE. lineatadecreased, whereas the visits byA. nigrumincreased.Z. trifollidisappeared completely towards the end of the season. Only two thirds of the pollination days were “good” foraging days for these visitor species. The four major visitor species spent an average of 11.7, 27.4, 30.7 and 22.6 s per flower, respectively. Estimates suggest that about 6.5 visits (which is equal to 2.6 min of flower‐visiting) and 2100 grains of pollen were required to produce one seed.