Plant-pollinator interactions : effects of population size on long term sustainability of a bog species, Comarum palustre (Rosaceae)

In Belgium, fens and bogs have largely been destructed since the middle of the 19th century. Especially in the Ardennes where bogs had once been continuous, today, they are highly fragmented and isolated. Nowadays, habitat fragmentation is one of the most important threats to biodiversity. Decreasing patch size may lead to reduced and isolated plant populations and to an increased extinction risk of remnant populations, also affecting plant-pollinator networks. Remnant populations are affected by demographical, genetic and environmental stochasticity leading to genetic erosion. 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 three flowering seasons. Insects belonging to the family Apidae were among the main visitors. Analyses of corbicular pollen loads did not show high fidelity to C. palustre (2008). Still, this does not seem to have an influence on its reproductive success since the species did not suffer from pollen limitation in the two flowering seasons analysed so far (2008 and 2009). Furthermore, fluorescent dye imitating pollen flow was dispersed over the whole population size (up to 200m) in three of the four investigated study sites. This suggests that there is at least an effective gene flow within populations