Last updated July 5, 2018 at 9:48 am
UK study finds key pollinators thrive in urban areas, but do less well in the country.
Agricultural land may be “a barren landscape for pollinators”, according to UK biologists who found that bumblebees (Bombus terrestris) fare better in concrete jungles than farms.
In a paper published in the journal Royal Society Proceedings B, biologists led by Ash Samuelson of the Royal Holloway University of London, UK, reveal the results of an experiment that correlated bee breeding success against land use.
The scientists first caught 176 wild queen bees in London’s Windsor Great Park. Mindful of biosecurity concerns, they then examined them all, rejecting any that showed signs of sickness or parasites.
Eventually, 43 were selected and induced to found captive colonies.
Where have all the flowers gone?
These were then placed in carefully selected sites, of varying levels of urbanisation, in and around London, including the crowded CBD, leafy suburbs, and in surrounding agricultural areas.
Samuelson and colleagues then monitored each colony at least once a week, noting reproductive success, the amount of stored food, together with the health and longevity of the insects.
The results were unambiguous: colonies in built-up areas did far better than those in agricultural zones.
This was only partly a surprise. The researchers had hypothesised that suburban bee colonies would do well because of “the combination of abundant gardens and proximity to semi-natural habitat”.
The presence of lots of flowers as the source of bumblebee good fortune, however, could not be advanced to explain their success in the inner-city.
“We found no direct effect of the proportion of flower-rich habitat surrounding colonies on colony success,” the scientists observed.
However, lack of visibility does not necessarily mean lack of presence. Samuelson and colleagues readily admit that the extent of nutritious flora in central London is unknown “due to access restrictions to gardens”.
The scientists suggest a couple of reasons to explain the comparative lack of success found in bee colonies situated in the country.
Appearances to the contrary, the extent of large single-crop fields may mean that bee food-plants are in numerically short supply. As well, they note, possible exposure to harmful agricultural chemicals could not be ruled out.
Urban versus rural
Kit Prendergast is a PhD student at Curtin University who studies native bees in urban environments, who was not involved in the study, said she was not surprised by the results.
She believes there are several reasons that urban areas may be better for bees.
“Many greenspaces still exist [in cities]. These include not only remnant natural vegetation, but also public and private parks and gardens.
“Park and gardens often boast a high diversity of flowers, including nectar-rich species that are key resources to bees. This contrasts with the monocultural plantations in rural areas,” she said.
“Flowering plants in cities also tend to be maintained year-round, compared with the short peak of many crop species, which means that, if there are not natural flowering resources in the surrounds, once the crop ceases flowering, bees are left without food.
“Herbicide and pesticide use tends to be lower in urban areas compared with rural, again improving the plight of urban bees compared with their rural counterparts given that “weeds” can be key resources for bees, and many pesticides are known to harm bees, respectively.”
If well managed, cities can be important habitats for the conservation of bees, Prendergast said.