Does your garden taste as good as it looks?

Bees in the UK have lost nearly all their natural habitat and gardens now provide a vital source of food, but gardeners are planting more exotic plants in their gardens. Do native bees share our adventurous tastes?

Spring is coming to the northern hemisphere, whether it’s ready or not and for many people that means more time in the garden. Gardeners will be working on their floral displays and planting for scents. But will local wildlife also enjoy the garden?

Insects have co-evolved with native plants over thousands of years. However many gardeners like to enliven their gardens exotic species from around the world. What does this mean for creatures like bees? Mick Hanley, Amabda Awbi and Miguel Franco of Plymouth University set up a study to find out.

The UK is part of the Palearctic ecozone. It’s a wide region as the map shows and not only do many British garden plants come from this region, bumblebees are found through the region too. Hanley et al. note they’re also found in North and South America, so while British bumblebees wouldn’t normally expect to find exotic plants, the plants themselves would be used to hosting bees. So do British bees have a taste only for British plants, or do they have a taste for foreign food?

Hanley’s team put a street in central Plymouth under the microscope. In summer 2010 they walked the street twice-weekly to see what plants were attracting the bees.

Classifying what garden plants the bees visit is surprisingly contentious. Gardeners will happily admit to growing Digitalis purpurea (foxglove) and Meconopsis cambrica (Welsh poppy), but would someone claim their display of overgrown brambles, buttercups and dandelions are gardened?

If you exclude the plants the gardeners did not deliberately plant, then the results are good news. They spotted bees feeding in both Palearctic and exotic plants. On the whole bees went where they could find food.

“Urban gardens are increasingly recognised for their potential to maintain or even enhance biodiversity,” Dr Hanley said. “In particular, the presence of large densities and varieties of flowering plants supports a number of pollinating insects whose range and abundance has declined as a consequence of agricultural intensification and habitat loss. By growing a variety of plants from around the world, gardeners ensure that a range of food sources is available for many different pollinators. But until now we have had very little idea about how the origins of garden plants actually affect their use by our native pollinators.”

In fact, the UK’s most common species Bombus terrestris the ‘buff-tailed bumblebee’ actually preferred the exotic plants, but not all bees shared the same tastes. Bombus hortorum the long-tongued ‘garden bumblebee’ much preferred native plants. For these bees the native plants, including the weeds, were very important.

Dr Hanley said: “If native plants were to disappear completely from our towns and cities, the long-term survival of some of our common pollinators – like the ‘garden bumblebee’ – could be in jeopardy. In addition to growing truly native plants like foxgloves, where possible, gardeners can help native pollinators by setting aside a small area to allow native brambles, vetches, dead nettles, and clovers to grow. But as long as some native species are available in nearby allotments, parks, or other green spaces, a combination of commonly-grown garden plants from all around the globe will help support our urban bumblebees for future generations.”

This last point comes across in the research paper. Hanley et al. refer back to other work on butterflies and note that while you might see a uniform distribution of species within an urban area, dietary specialists can be much less common in urban than rural sites. Likewise some bees have special dietary needs and change of house owner and remodelling of the garden could have serious consequences for a fussy eater.

Hanley et al. conclude helping biodiversity in urban areas shouldn’t just be gardeners’ burden. They also argue that civic authorities can play their part with parks and other green spaces. This would seem to mesh well with Lionel Smith’s work on developing grass-free lawns.

You can pick up Hanley et al.‘s paper Going native? Flower use by bumblebees in English urban gardens with free access from the Annals of Botany.

Images

The Palearctic Zone by Lokal Profil / Wikipedia. [cc]BY-SA[/cc]

Meconopsis Cambrica (Welsh poppy) by Carmona Rodriguez / Flickr. [cc][/cc]