The biggest threat to biodiversity is urbanization. However, little is known by scientists about how urbanization impacts ecosystem services and biodiversity in tropical parts of the Global South.
Large solitary cavity-nesting bees such as Carpenter bees (Xylocapa spp.) can benefit from urbanization provided they find enough flower resources. Image Credit: Vikas S. Rao
In collaboration with the University of Agricultural Sciences of Bangalore in India, an international research team led by the German universities of Göttingen and Hohenheim looked into the effects of urbanization on bee communities in smallholder farms in and around Bangalore, a city in South India with a population of more than 13 million.
Contrary to findings from temperate locations, they discovered that social bees, such as wild honey bees, suffered more than huge solitary bees or those that nest in holes. Native flowers close to farms and agricultural diversity can support the survival of bee populations. Ecological Applications, a publication, reported the findings.
The researchers tallied more than 26,000 individual bees from 40 species during a thorough field study of bees on vegetable fields spanning rural and urban habitats.
The scientists were able to determine how the percentage of sealed surfaces and buildings in urban areas influenced bee colonies by combining the data with remote sensing from satellites.
They also compared bees that use various nesting locations and have various social structures and levels of mobility to examine how the various bee species reacted to the settings.
We demonstrated that the way bees responded to urbanization were specific to certain traits. For example, bees nesting in cavities actually benefited from urbanization as they can nest in small cracks and cavities on buildings.
Gabriel Marcacci, Study Lead Author and PhD Student, Functional Agrobiodiversity, University of Göttingen
Marcacci added, “Moreover, we found that ground-nesting bees, which are usually considered the losers in urbanization, find ample nesting opportunities in tropical megacities because enough bare ground is still available, mostly in the less developed neighborhoods.”
Our results differ in part from what is often found in cities in temperate regions, which shows that we cannot generalize from field studies carried out in Germany or other countries of the Global North.
Ingo Grass, Professor, Department of Ecology of Tropical Agricultural Systems, University of Hohenheim
Another striking outcome of urbanization is the sharp drop in social bee populations.
This result is particularly worrying because in the tropics, social bees—such as wild honeybees and stingless bees—form large colonies and are essential for crop pollination.
Teja Tscharntke, Professor, Department of Crop Sciences, University of Göttingen
The study also showed that farm management measures like crop diversity or the presence of native wild plants in and around vegetable fields have a favorable impact on bee colonies.
Our results suggest that urban agriculture can promote bee communities if managed in a sustainable manner and could combine to support wild bee conservation and food production in and around cities.
Prof. Catrin Westpha, Head, Functional Agrobiodiversity, University of Göttingen
Journal Reference:
Marcacci, G., et al. (2022 Functional diversity of farmland bees across rural-urban landscapes in a tropical megacity. Ecological Applications. doi:10.1002/eap.2699.