Evidence of pollinator declines
There is widespread concern about both wild and managed pollinator populations in a number of geographic regions. Managed populations of the domesticated honey bee have suffered recent regional losses (59% loss of colonies between 1947 and 2005 in the USA (van Englesdorp et al. 2008) and 25% loss in central Europe between 1985 and 2005 (Potts et al. 2010)), due to outbreaks of pests and diseases, genetic diversity issues and environmental stressors.
Many species of wild pollinator such as bumble bees, solitary bees and hoverflies are also under threat. In the UK and the Netherlands, Biesmeijer et al. (2006) found landscape scale declines in native bee species richness. They compiled almost 1 million records of native bee and hoverfly species before and after 1980 from national databases and reported that the number of bee species declined significantly in 52% of the 10 x 10km squares analysed in the UK, and in 67% in Dutch squares. Conversely, bee diversity increased in only 10% and 4% of squares respectively. Similarly, both hoverfly and and bee communities have gradually become dominated by a few common species, with 29% fewer bee and hoverfly species occurring in Britian after 1980. Reliance on a such a small group of pollinators for plant pollination is risky because the community may not be resilient to future variations in climate, resource provision and disease outbreaks. In parallel to these trends, Biesmeijer et al. also found that the number of plant species that rely on insect-pollination had also declined in the same period, while species pollinated by wind or water were increasing.
Other studies have shown similar trends. Since the 1950s, 13 bumblebee species have disappeared from at least one European country, and in the UK, 3 of the 25 native species have gone extinct, with a further 8 suffering major range contractions (Goulson et al. 2008). The declines are not just occuring in Europe: Cameron et al. (2011) have shown that over the last 30 years in the USA, sharp declines of up to 96% in the abundance of bumblebees have occurred, although there are fewer sources of baseline data for other groups of pollinators.
Biesmeijer, J.C., et al. 2006. Parallel declines in pollinators and insect-pollinated plants in Britain and the Netherlands. Science 313: 351-354
Cameron, S.A., et al. 2011. Patterns of widespread decline in North American bumble bees. Proceedings of the National Academy of Sciences of the United States of America 108: 662-667
van Engelsdorp, et al.. 2008. A survey of honey bee colony losses in the US, Fall 2007 to Spring 2008. Plos One 3, e4071
Goulson, D. et al. 2008. Decline and conservation of bumble bees. Annual Review of Entomology 53: 191-208
Potts, S.G. et al. 2010. Declines of managed honeybees and beekeepers in Europe? Journal of Apicultural. Research 49: 15–22