Source Article: Baldock, K.C.R., Goddard, M.A., Hicks, D.M., Kunin, W.E., Mitschunas, N., Morse, H., Osgathorpe, L.M., Potts, S.G., Robertson, K.M., Scott, A.V., Staniczenko, P.P.A., Stone, G.N., Vaughan, I.P., Memmott, J., 2019. A systems approach reveals urban pollinator hotspots and conservation opportunities. Nature Ecology and Evolution, 3: 363-373. https://doi.org/10.1038/s41559-018-0769-y
Pollinators in a changing world
One third of all agricultural output in the United States depends on pollinator species for production, and this estimate does not even include pollinated crops that wild animals such as birds and bears depend on as part of their diets. Many of us think of honeybees when we hear the word “pollinator” but there are a wide variety of insects and other animals that pollinate plants. Did you know that bats are important pollinators in tropical and desert environments?
But pollinator populations are on the decline. As the human population grows, habitats rich in flowers and plant-life that support pollinators are transformed to urban landscapes. This habitat loss leads to a decrease in pollinator populations. Another additional stress on pollinators has been the widespread use of pesticides in agriculture. Bees exposed to pesticides display impaired foraging skills and a decline in their immune systems, sometimes leading to death.
Pollinators in urban environments
While it might seem counterintuitive, there are lots of pollinators present in urban environments. Pollinators such as bees and hoverflies find refuge in public parks, cemeteries, and gardens. Katherine Baldock from the University of Bristol (UK) and her colleagues recently published a study that examined how pollinator species used different urban spaces in four British cities (Bristol, Reading, Leeds, and Edinburgh). They wanted to understand where pollinator species were most abundant and how future urban planning could increase pollinator populations in urban spaces.
The abundance of bees and hoverflies was highest in community and home gardens and lowest on man-made surfaces. Average bee abundance was up to 52 times higher in these garden habitats!
Baldock and her colleagues examined pollinator species and their abundance in nine different urban spaces within each city: community gardens, cemeteries, home gardens, man-made surfaces (e.g. industrial estates, parking lots), other green spaces, city parks, sidewalks, nature preserves, and road verges (the space between the road and the sidewalk). The abundance of bees and hoverflies was highest in community and home gardens and lowest on man-made surfaces. Average bee abundance was up to 52 times higher in these garden habitats! Interestingly, they did not find a difference in the number of bee and hoverfly species between the nine examined habitats.
Not surprisingly, areas with higher flower abundance have more pollinators, and flower abundance was higher in community and home gardens. Home gardens in wealthier neighborhoods support more pollinators because there are a variety of different plant species present in these gardens. In total, the researchers estimate that home gardens contain 54-83% of the pollinators in the four cities. Even though community gardens contain a high amount of bees and hoverflies, they typically only occupy less than 1% of the land space in each city.
Suggestions to improve pollinators in urban cities
Based on their results, Baldock and her colleagues make several suggestions for how urban planners can support pollinator communities in their cities. The main suggestions are to increase the quantity of land favorable to pollinators and to improve the quality of existing land through better management. In particular, their results showed that increasing the amount of community gardens would have the greatest positive impact on pollinator populations in three of the cities. Additionally, an increase in the abundance of floral species in road verges and public parks would significantly increase pollinators. One easy method to increase the abundance of plants would be to reduce mowing of these spaces, since many common plants have been shown to increase in abundance when mowing is reduced. Lastly, in order to support pollinator populations in lower-income neighborhoods, cities could preferentially invest in community gardens and other initiatives in lower-income areas to help reduce the inequalities in the distribution of pollinators.