Temporal changes in pollen flow and neighbourhood structure in a population of Saxifraga hirculus L.

Abstract

The population are of flowering shoots of the perennial herb, Saxifraga hirculus, reaches a max. of 134 m2 and an overall density of flowers/m2 of 11.4. The flower is mainly visited by a syrphid sp., Eurimyia lineata, and to a lesser extent by another syrphid Neoscia tenur, a moth, Zygaena trifolii, and a fungus gnat, Asindulum nigrum. The distribution of the interfloral flight distance is leptokurtic. The mean flight distance of the visitors is 101 cm. 10% of the flights are much longer (2-8 m: cross-flower patch, and about 20 m: cross-population flights). If they are not included, the mean of flights (<1.7 m) becomes 28 cm. These flights become shorter with increasing flower density. The visitors do not have a nearest-neighbour foraging pattern. They visit on average the 8th nearest neighbour. The distribution of flight directions is uniform. Seed dispersal distances have a leptokurtic distribution and a mean dispersal distance of 13 cm. The ecological neighbourhood area is 66.4 m2 and 64.9 m2 assuming normality and allowing for leptokurtosis. Z. trifolii with its large proportion of long flights increases the size of the neighbourhood area considerably. The mean flight distance (<1.7 m) is correlated with neighbourhood area. The evolutionary impact of moths and butterflies to plant population structure is stressed.