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 al pine population of the circumpolar Ranunculus acris (Ranunculaceae) at Hardangervidda, southwest Norway. Dipteran families, mainly Muscidae and Anthomyiidae, were the most frequent flower visitors and pollinato rs. A single visit by these insects resulted in a seed set of c. 18% o f the total potential. Visitation rates were highest early in the flow ering season. The longevity of individual flowers of early flowering p lants was c. 3 d shorter than that of mid-season flowering individuals . Insect pollinators moved short distances between flowers and they mo stly visited near neighbour plants. Experiments showed that Ranunculus acris was self-incompatible and thus dependent on insect visitation f or seed production. Early flowering individuals had a very high seed s et relative to individuals flowering in mid- and late season, suggesti ng a strong selection pressure for early flowering in the population. Seed production in this Ranunculus acris population seems to be limite d by severe climatic conditions and a low pollination intensity.