Abstract
Mass‐flowering crops (MFCs) are increasingly cultivated and might influence pollinator communities in MFC fields and nearby semi‐natural habitats (SNHs). Across six European regions and 2 years, we assessed how landscape‐scale cover of MFCs affected pollinator densities in 408 MFC fields and adjacent SNHs. In MFC fields, densities of bumblebees, solitary bees, managed honeybees and hoverflies were negatively related to the cover of MFCs in the landscape. In SNHs, densities of bumblebees declined with increasing cover of MFCs but densities of honeybees increased. The densities of all pollinators were generally unrelated to the cover of SNHs in the landscape. Although MFC fields apparently attracted pollinators from SNHs, in landscapes with large areas of MFCs they became diluted. The resulting lower densities might negatively affect yields of pollinator‐dependent crops and the reproductive success of wild plants. An expansion of MFCs needs to be accompanied by pollinator‐supporting practices in agricultural landscapes.
Highlights
The decline of wild pollinators has raised serious concerns about the future of crop and wild plant pollination (Biesmeijer et al 2006; Garibaldi et al 2011; Gonzalez-Varo et al 2013)
We found a consistent negative relationship between the cover of pollinator-dependent mass-flowering crops (MFCs) and pollinator densities in MFC fields across Europe
This is the first evidence that an increased cultivation of MFCs decreases densities of bumblebees, solitary bees, honeybees and hoverflies in the MFC fields across regions
Summary
The decline of wild pollinators has raised serious concerns about the future of crop and wild plant pollination (Biesmeijer et al 2006; Garibaldi et al 2011; Gonzalez-Varo et al 2013). Even if increased use of managed pollinators (e.g. the honeybee, Apis mellifera L.) can provide some insurance, they cannot fully replace the loss of wild pollinators, since the yields of many crops relate more to the densities of wild pollinators than to that of honeybees (Garibaldi et al 2013). A possible reason is that intensification has caused pollinator declines, with negative consequences for crop pollination and yields (Deguines et al 2014). Alternative and untested hypothesis, is that the current expansion of mass-flowering crops (MFCs) could – according to the ‘landscape-moderated concentration and dilution hypothesis’ proposed by Tscharntke et al (2012) – cause a dilution of pollinator density with a negative effect on pollination services but without necessarily reducing pollinator population size. Between 1961 and 2006, the global cropping area has increased by 23%, of which 18–35% has been devoted to MFCs in the developed world and 23–33% in the developing world (Aizen et al 2008), partially driven by increasing demands for and subsidies to biofuels (Breeze et al 2014)
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