Pollen limitation affects progeny vigour and subsequent recruitment in the insect‐pollinated herb Ranunculus acris

Abstract

Pollen limitation on seed production appears to be widespread among the angiosperms. However, few studies have examined if pollen limitation affects population growth. We supplementally hand‐pollinated all flowers of 20 individuals of Ranunculus acris in the temperate meadow Rudsviki, Kaupanger, west Norway in 2003. The seed production did not respond to pollen addition, but the achene weight increased by 18% after supplemental pollination. To test whether this progeny quality response to the pollen‐supplementation experiment could contribute to population growth, we sowed achenes from hand‐pollinated plants and control plants into natural conditions in ten blocks at three densities. During the subsequent season (2004), the number of seedlings and juveniles (pooled) from hand‐pollinated plants were substantially (64%) higher than from controls. There was also a clear positive effect of seed sowing‐density on recruitment, suggesting that recruitment is seed‐limited in this system. However, the density of vegetative individuals in 2005 was generally low and did not differ significantly between plots that received achenes from control or supplementary pollinated plants. Our results show that pollen limitation may affect germination through seed quality, and thereby impact plant population dynamics. However, in our system it appears that other factors, such as intra‐ and interspecific competition, may have outweighed the potential contribution from pollen limitation on population demography.