Urban development has a significant impact on the habitats of many animal species. Pollination is an ecosystem function vital for terrestrial ecosystems and food security. However, a quantitative meta-analysis of the overall effects of urbanization on pollinator diversity and pollination service is lacking.

The team of researchers from Wuhan Botanical Garden (WBG), the Chinese Academy of Sciences and Martin Luther University Halle-Wittenberg (MLU) performed a comprehensive meta-analysis of 133 studies to examine how urban growth impacts pollinators and their pollination performance. The analysis considers all the Earth’s continents except Antarctica.

The results find that with urbanization, butterflies are particularly susceptible to changes in their environment. “They depend on very specific plants for their nutrition and larval development. Since these are found less and less in cities, the populations of many butterfly species are also declining,” explains Dr. LIANG Huan from WBG. Also particularly affected are pollinators that are already active in early spring and feed on the nectar and pollen of early flowering plants. Wild bees that nest in the ground often lack suitable breeding sites in cities and their populations are declining. Less affected, on the other hand, are wild bees that nest above ground, in cavities or in insect hotels.

Surprisingly, despite the negative effects of urbanization on pollinator diversity, the pollination performance measured by seed set is enhanced in non-tropical cities. According to the researchers, this is mainly due to the abundant generalists and managed pollinators therein.

"Honeybees are very productive and are kept by hobby beekeepers in many places,” says LIANG. While this is good for urban plants, it can negatively impact other pollinators because honeybees often displace other native pollinators and can transmit diseases to wild pollinators.

The results demonstrate the magnitudes of multiple moderators on urban pollinators and pollination services, emphasizing the importance of nature conservation measures in urban areas.

The study has been published in Ecology Letters entitled “The effects of urbanization on pollinators and pollination: A meta-analysis”. It was funded by the Chinese Academy of Sciences and the National Natural Science Foundation of China.