Shrinking habitats and food availability are causing their populations to decline, say scientists.
Butterflies and many wild bees that fly in early spring are being hit hardest by urban growth, according to global research by scientists at the Martin Luther University Halle-Wittenberg (MLU) in Germany and the Chinese Academy of Sciences.
But pollination has not yet been impacted because honeybees, for example, can compensate for the reduction of urban pollinators, according to the first comprehensive analysis of data from more than 130 previous studies.
The research team say their findings, published in the journal Ecology Letters, underline the importance of nature conservation measures in urban areas.
The expansion of cities around the world is having a significant impact on the habitats of many animal species due to factors including impervious surfaces, a reduction in plant diversity and more environmental pollution.
Researchers say that pollinators, whose work is essential for a thriving ecosystem and hence human food security, are being particularly affected.
Biologist Dr. Panagiotis Theodorou, of MLU, said: “There are many studies that have examined the relationship between urbanization, pollinators and pollination performance and have found negative effects.
“Because this work is very complex and time-consuming, the studies are usually limited to specific cities or regions.”
To obtain a global overview, Theodorou and Chinese scientists analyzed data from 133 different studies that looked at how urban growth impacts pollinators and their pollination performance.
The analysis takes into account all of the Earth’s continents except Antarctica.
Theodorou says the results paint a “clear” picture.
He said: “As urbanization increases, the abundance and biodiversity of many pollinators decrease.”
However, he said certain groups are more affected than others. The team found that butterflies were the most negatively impacted.
Dr. Huan Liang, of Chinese Academy of Sciences, said: “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.”
The findings also showed that pollinators that are already active in early spring and feed on the nectar and pollen of early flowering plants are “particularly” affected.
Theodorou explained that wild bees that nest in the ground often lack suitable breeding sites in cities and their populations are declining.
But wild bees that nest above ground, such as in cavities, are less affected.
The research shows that the declining numbers do not necessarily result in a decrease in pollination performance.
Pollinators still regularly pollinate plants, which produced enough seeds to propagate.
The research team explained that is mainly due to honeybees, which, together with bumblebees, compensate for the reduction in urban pollinator diversity.
Liang said: “Honeybees are very productive and are kept by hobby beekeepers in many places.
“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 analysis also shows that cities with a greater diversity of flowers are usually home to more and many different types of pollinators.
Theodorou added: “If we design our cities better in terms of what they offer to pollinators, we can at least compensate for some of the negative consequences of urban growth.”
Produced in association with SWNS Talker
Edited by Saba Fatima and Asad Ali
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