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The UK has two dozen species of bumblebee, all of which are being affected by our impact on the environment.
Improvements can be made, but not all species can be saved in the same way. A new report lays out how we can prioritise the best selection of habitats to give these pollinators a boost.
Bumblebees need a wide variety of habitats if they are to recover from population declines across the UK.
A study from the British Ecological Society found that no one habitat in the country will help all bumblebee species, including several threatened ones, to thrive. The preservation of patches of urban, rural and agricultural areas is vital to their conservation.
Lead author Dr Penelope Whitehorn says, 'Our results suggest that reversing the loss of semi-natural areas such as wetlands may be the single most generally effective action for bumblebee conservation, while improving habitats in urban and arable areas could benefit certain rare species.
'As one of the most nature-depleted countries in the world, it's really important that we better protect our native species and habitats in the UK.'
The scientists published their research in the Journal of Applied Ecology.
The UK supports around 10% of the world's species of bumblebee. The 24 species play a vital role in pollinating agricultural crops and other plants worth hundreds of millions of pounds and help ensure food security.
As early as the 1950s, scientists became aware that bumblebee populations in the UK were in decline. Three of the UK's native bumblebees have become extinct, with species maps drawn up in the 1980s revealing the existence of a 'central impoverished region' spanning from Lincolnshire to Somerset where species diversity dropped by around a third since the 1960s.
While the exact reason of bumblebee decline remains uncertain even to this day, a number of key factors are known to have an impact.
Rising temperatures due to climate change are one important factor. The increasing number of unusually hot days is increasing local extinction rates for bumblebees across Europe and North America, while forcing survivors to move to stay within their preferred climate conditions.
Pesticides and pollution are also having an impact. Pesticides known as neonicotinoids have been banned in recent years due to their impact on bees, but the effects of their replacements are not as well understood. Air pollution, meanwhile, hinders the ability of bees to find flowers and consume their nectar, increasing the risk of starvation.
But the primary cause is believed to be land use change. Agricultural intensification following the second world war saw 97% of unimproved grassland lost, dramatically reducing the availability of plants such as the red clover which bumblebees depended upon.
Conversion to farmland and fragmentation of their remaining habitat has seen bee richness decline across 75% of sites in England and put their populations under threat. Similar changes are affecting bumblebees across Europe.
Co-author Richard Comont, from the Bumblebee Conservation Trust, says, 'Bumblebees are mostly threatened by loss and degradation of nesting and feeding habitat.
'They need areas with lots of flowers available from March right through to October. Bees lose this vital resource when habitats are lost entirely because they're either built on or changed into other environments or degraded through things like pesticide use.'
The current study investigated bumblebees, using community science data collected over a decade to assess how different species responded in a range of environments. The researchers found that a one-size-fits-all policy is unlikely to help bumblebees overcome the challenges that face them.
During the survey, members of the public were asked to walk the same route monthly from March to October, and record the different bumblebees they saw. These species were later verified by specialists to confirm the presence of a particular species.
The location of the route was then used to assess the different habitats along the way, as well as the area's temperature, elevation and rainfall.
The study found that peri-urban and semi-rural habitats, where urban areas give way to rural land, have some of the largest effects on bumblebee counts, with tree bumblebees and buff-tailed bumblebees thriving in these habitats while rarer species fared more poorly.
Meanwhile, wetland habitats supported two species of carder bee, including the Vulnerable Bombus muscorum. More intensively managed areas, such as farmland and urban areas, saw increased numbers of other species.
Together, the results suggest that a range of habitats will be needed to effectively conserve all of the UK's bumblebee species. The researchers suggest that the restoration of wetland will have important benefits for bumblebees and other species, with the UK having lost 90% of this habitat in the past century.
While the findings are significant, the scientists acknowledge that the routes taken by the community scientists are often closer to urban areas than by chance, as individuals walk near their homes. This could bias the results into greater effects for these areas than may be present.
The historical ranges of bees, and bursts of high activity by certain species at different times of the year, may also skew the findings.
However, the study argues that the effects have been eliminated as much as possible, and those remaining are outweighed by the benefits of creating such a large dataset. In future, researchers hope to build on this to help inform future conservation strategies, such as the creation of 'bee highways', or B-Lines, across the UK.
Penelope says, 'We'd like to find out why different species are associated with different habitats, so we can create and preserve the right conditions for them in the future. We also need to better understand how shifting climate and land uses might affect bumblebees and their habitats.'