INTRASEASONAL VARIATION IN POLLINATION INTENSITY AND SEED SET IN AN ALPINE POPULATION OF RANUNCULUS-ACRIS IN SOUTHWESTERN NORWAY

I studied aspects of the pollination and reproduction ecology of an alpine population of the circumpolar Ranunculus acris (Ranunculaceae) at Hardangervidda, southwest Norway. Dipteran families, mainly Muscidae and Anthomyiidae, were the most frequent flower visitors and pollinators. A single visit by these insects resulted in a seed set of c. 18% of the total potential. Visitation rates were highest early in the flowering season. The longevity of individual flowers of early flowering plants was c. 3 d shorter than that of mid-season flowering individuals. Insect pollinators moved short distances between flowers and they mostly visited near neighbour plants. Experiments showed that Ranunculus acris was self-incompatible and thus dependent on insect visitation for seed production. Early flowering individuals had a very high seed set relative to individuals flowering in mid- and late season, suggesting a strong selection pressure for early flowering in the population. Seed production in this Ranunculus acris population seems to be limited by severe climatic conditions and a low pollination intensity.