Biodiversity: bees work better in the city

Biodiversity: bees work better in the city

February 06, 2020

Biodiversity: bees work better in the city

A German study highlights the differences between the countryside and the city as regards the work of pollinators, underlining the importance of designing “bee-friendly” cities 

It might seem like a paradox, but pollinators - and in particular bees and bumble bees - are much more efficient in their work if they are in an urban setting rather than rural settings. This is explained in the journal Nature Communication by a team of German researchers working in centers that study the environment and biodiversity, including the German Centre for Integrative Biodiversity Research (iDiv)Università Martin Lutero di Halle-Wittenberg (MLU) and the Helmholtz Centre for Environmental Research (UFZ).

Urbanization is one of the driving forces behind the changes in biodiversity we are seeing globally, negatively affecting some species and creating new opportunities for others,” explain the authors. “To date, however, the impact of urbanization on ecosystem services is poorly studied” they add, including among these “services” the pollination carried out to a large extent by insects. 

Biodiversity champions in danger

There is no doubt that pollination is crucial for the health of ecosystems and the maintenance of biodiversity: according to estimates, 87.5% of angiosperms (also known as “flowering plants”) depend precisely on animals for pollination and for their seeds to be dispersed. As FAO point out, almost all bee species (there are over 25,000 of them) are good pollinators and together with other insects such as wasps, butterflies, flies and cockroaches, they represent the vast majority of pollinators. 

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In the anthropocene era - dominated by human activities - the work and the very existence of these precious biodiversity allies is in serious danger, not only in the environments most directly linked to the presence of man such as cities, but also in the countryside, especially on land used for agricultural purposes. In fact, agriculture based on a single type of crop inevitably reduces biodiversity among plants and consequently among pollinating insects. Furthermore, the use of pesticides to eliminate unwanted species also has an important negative impact on the survival of many pollinators, first of all bees, which are particularly sensitive to these substances. 


The resilience of bees

In the study published by Nature Communication, German researchers used an experimental design that allowed the impact of urbanization on the biodiversity of pollinators, but also on their pollinating efficiency, to be directly compared. 

The results of the analysis carried out in 9 German cities and in the surrounding rural areas showed that the cities are less rich than the neighboring rural areas in terms of the number of insect species present. Looking more carefully, we can see that in the cities, diptera (such as flies) and lepidoptera (butterflies) are missing, while hymenoptera - especially bees - were richer in terms of the number of species and more active in “visiting” flowers. And in these very urban areas, the pollination values calculated by the researchers were higher. There are many reasons for these differences between the countryside and the city. The most important one is the presence in the city of many possible “shelters” for bees, such as wall cavities for bumblebees, dead wood for potter wasps and exposed areas of land for digger wasps. “Cities are extremely dynamic environments and bees, with their sophisticated neurosensory skills, such as well-developed learning and memory, might have an advantage in adapting to these places compared to beetles, diptera and lepidoptera” explain the researchers, underlining the great resilience of bees. Creating “bee-friendly” cities could therefore be important for the survival of these insects and their fundamental work of pollinating flowers and crops in urban areas.

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