The habitat effect on the diversity of pollen resources in several Campanula spp. – an implication for pollinator conservation

Abstract

Lack of pollen, a main protein source, is widely regarded as one of the causes of pollinator decline. This study investigated the potential mass of Campanula patula L., Campanula persicifolia L., Campanula glomerata L., Campanula bononiensis L., and Campanula trachelium L. pollen that can serve as food for insect visitors. Observations and measurements were made during the period 2006–2008 on two separate sites for each species (in natural or semi-natural vs. man-made habitats). The study site was situated in the agricultural landscape on the Lublin Upland, south-eastern Poland (51°18ʹ27ʹʹN, 22°26ʹ05ʹʹE). The total pollen yield was restricted by various biotic parameters (anther size and pollen viability) and abiotic factors (habitat and/or meteorological conditions). Therefore, the pollen production may differ considerably among species and the reward of the same species can be variable among habitats and growing seasons. The total pollen yield was higher on natural and semi-natural habitats (3.7–12.7 g per 10 m2 plot) compared to man-made habitats (2.9–4.8 g per 10 m2 plot). The main visiting insects are bees, although flies and beetles have also been recorded. Consequently, Campanula species are important in supporting general insect biodiversity within various ecosystems and indirectly influence pollination services and biocontrol in agroecosystems. To maximize the abundance and diversity of bees and other pollinators in the surroundings of agroecosystems, natural and semi-natural habitats with an adequate quantity of food supplementation, rather than man-made habitats, are indispensable. However, in the landscape context, the minimum size of high quality fragmented natural and semi-natural patches may differ considerably.