Foraging and nesting ecology of bumblebees (Bombus Spp.) in agricultural landscapes in Sweden

The aim of the thesis was to investigate in what way different agricultural landscapes and management routines affect the abundance and performance of bumblebees. The studies were conducted in the surroundings of Uppsala, in mid Sweden. The area consists of both intensive, large-scale farming and small agricultural fields surrounded by pastures, forests and lots of boundaries. Both the local habitat type and the amount of forest in the surrounding agricultural landscape affected bumblebee queens searching for nesting sites. Boundaries, together with other uncultivated areas, showed the highest densities of nest-seeking queens. Different bumblebee species chose nesting sites in different habitats. Few of the available plant species were used as foraging source for the bumblebees. The highest frequency of foraging bumblebees was found in clearings, road boundaries and pastures. There was a negative correlation between the number of nest-seeking bumblebees in spring in a habitat and the number of foraging bumblebees there the following summer. The most frequently visited plant species for bumblebees in general were preferred by all observed bumblebee species. Differences "castes" were found to prefer different plants. Two declining bumblebee species in the agricultural landscape, Bombus sylvarum and B. subterraneus, both forage on plant species preferably growing in boundary habitats. For prevalence of these species, such habitats have to be conserved in the modern agricultural landscape. A greater abundance of foraging bumblebee queens in spring was estimated in areas with a high volume of Salix caprea per ha (>1000 m³ crown volume). In areas with low volumes of S. caprea per ha (<100m³), there is higher competition for food resources. Thus, it is recommended that even small willows, which can have high flowering percentage, be preserved in the agricultural landscape. Plantations of short-rotation energy forests can also be used by bumblebees as a complementary foraging source. Trees and juniper shrubs (Juniperus communis) have a positive effect on the species richness of foraging bumblebees within semi-natural pastures and the proportion of arable fields and urban elements per km² surrounding area affected the bumblebee community structure positively. Bumblebees and butterflies were negatively affected by increasing grazing pressure. These results led to a recommendation to conserve management heterogeneity, i.e. grazing pressure and tree and shrub layer, within the semi-natural pastures.

Author

• Birgitta Svensson

• bombus
• animal ecology
• plant animal relations
• foraging
• animal feeding
• nesting
• farmland
• landscape
• sweden
• bumblebees
• nesting sites
• willows
• Salix caprea
• habitat selection
• agricultural landscape
• semi-natural pastures
• heterogeneity

Repository record dc:identifier.uri

https://pub.epsilon.slu.se/223/

OAI identifier oai:identifier

oai:pub.epsilon.slu.se:223