Open access publications in the SLU publication database

Abstract

Pollinators uphold important ecological functions and their economic and ecological importance is considerable. In the present thesis the relationship between management practices and the behaviour, diversity and composition of four flower visitor groups: bees, butterflies, hoverflies and beetles, are examined in grasslands with different grazing intensity and in different landscapes in East-Central Sweden. Four flower visitor groups were influenced by grazing intensity in different ways. Hoverflies and beetles were positively related to vegetation height, while bees and butterflies were not. In the latter two groups some species were favoured by short vegetation. Hoverflies were more species rich in forested landscapes, whereas butterfly species richness was lower in areas containing many roads. Bees showed the most complex responses mainly due to their diverse life-history strategies corresponding to different environmental factors. The species richness of nest-parasitic and soil nesting bees was favoured by intensive grazing and the existence of bare soil. Cylinder-nesting solitary bees were little affected by management, and high species richness was associated with eutrophication and low plant species richness. The reproductive output in this group can be measured by produced offspring biomass, and this related mainly to human activity. Bumblebees were influenced mainly by landscape factors and long-tongued species appearing late in the season were especially dependent on landscape connectivity and grassland cover. To maintain viable populations of flower visitors, alternative grazing strategies are recommended. To maintain a high diversity of flower visitors in isolated grasslands local optimisation of grazing may be the best strategy. In interconnected landscapes a better strategy may be to vary grazing intensity at the landscape level. Grasslands with different grazing management could thus complement each other. In landscapes where conditions are particularly good for specific insects, a third alternative would be to manage the landscape to enhance the diversity of this particular group.