Effects of population size on pollinator guild, reproductive success and long term persistence of Comarum palustre (Rosaceae)

The great majority of flowering plants in temperate regions depend on insects for pollination and reproductive success. Habitat fragmentation resulting in small and isolated plant populations are major threats to plant-pollinator networks. Remnant populations are affected by demographical, genetic and environmental stochasticity leading to genetic erosion. This threatens the ability of populations to respond to altering selection pressures such as climate change. Comarum palustre is a perennial herb growing in highly fragmented bogs in the Ardennes in Belgium. We investigated whether population size influences its reproductive success. Flower observations, pollen limitation experiments and pollen dispersal measures with fluorescent dye were conducted in small and large populations of C. palustre from 2008 to 2010. Significantly more insects were visiting C. palustre in large compared to small populations in the two flowering seasons analysed so far (2008 and 2009). Still, this does not seem to have an influence on its reproductive success since the species did not suffer from pollen limitation. Fluorescent dye imitating pollen flow was dispersed over the whole population size (up to 200m) in three of the four investigated study sites. Observed differences in the fourth site maybe explained by the height and density of the surrounding vegetation. Dye dispersal patterns will further be related to population genetic structure.