Chemical signatures of floral resource competition between honeybees and wild bees along a landuse gradient
Zusammenfassung der Projektergebnisse
The project investigated the influence of land use and competiton from honeybees on colonies and populations of bumblebees (Bombus spp.) in agricultural landscapes of Germany. All studies were conducted in the framework of the Biodiversity Exploratory project. We found no effect of competing honeybees on bumblebees, whereas land use affected bumblebees via changes in floral resource composition. The project revealed insights with regard to the origin of bumblebee pollen early in the season. In the rainy spring of 2013 experimental Bombus terrestris colonies collected on average 80 % of pollen from woody plants, with 34 % belonging to the genus Acer. Early colony growth positively correlated with total amount of woody pollen and protein collected and decreased with increasing proportions of semi-natural habitats and total amino acid concentrations, suggesting that pollen quantity is more important for B. terrestris than pollen quality. Across grassland plots in the Schwäbische Alb, the abundance of 13 species of bees (12 Bombus spp. and A. mellifera) responded negatively to land use (three of them significantly), while no species responded positively. The degree of resource specialisation did not determine a bee species’ land use response, while there was a link between the responses of bumblebees and those of their preferred food plants. The extractive footprint method was successfully used in quantifying variation in bumblebee visitation on Lotus corniculatus across plots, providing the unexpected result that visitation frequencies were highest in the most heavily used grasslands, presumably because bumblebees in sites with low plant diversity had even fewer remaining options with regard to alternative floral resources. In consequence, pollination services to those few surviving plants may not decline with land use intensity. While the extractive footprint method worked well to quantify bumblebee visitation on Lotus corniculatus, results were ambiguous for Trifolium repens, partly due to non-Bombus substances in the chemical background obscuring bumblebee footprints. Thus, while the extractive footprint method holds many advantages for quantifying bumblebee flower visitation in mutli-replicate field studies, its application requires a priory testing for each species of flowering plant and in each ecological context.
Projektbezogene Publikationen (Auswahl)
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(2016) Evaluating the effects of floral resource specialization and of nitrogen regulation on the vulnerability of social bees in agricultural landscapes. Apidologie: 1-13
Kämper, W, Weiner, CN, Kühsel, S, Storm, C, Eltz, T, Blüthgen, N
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(2016) How landscape, pollen intake and pollen quality affect colony growth in Bombus terrestris. Landscape Ecology 31 (10): 2245-2258
Kämper, W, Werner, PK, Hilpert, A, Westphal, C, Blüthgen, N, Eltz, T, Leonhardt, SD
