Cities eliminate less mobile species and favour those that thrive at higher temperatures. This is the conclusion of a field study conducted in 81 places in Belgium. ‘For the first time, we see how urbanization consistently decreases biodiversity on a large scale’, says researcher Frederik Hendrickx from the Royal Belgian Institute of Natural Sciences (RBINS).
Belgium has a population density of 300 people per square kilometre and is one of the most urbanized countries in Europe. Worldwide, studies estimate that urbanization will have tripled by 2030. Biologists from the Royal Belgian Institute of Natural Sciences studied the effect of urbanization on natural species communities using ground beetles.
Urban heat islands
They compared species composition in rural and urban areas by installing insect traps at 81 places scattered throughout Belgium. The result: heat tolerating beetle species were much more common in cities compared to the countryside. Cities are ‘heat islands’ with a lot of heat-absorbing materials, like concrete. Because of the fragmentation of green areas, cities also appear a dead-end for short-winged beetle species. Those species are less mobile and not able to migrate to the next green spot when their habitat is converted. In urban Belgium, there are almost exclusively beetle species with long wings, the study says.
‘Urbanization makes insect faunas uniform’, says biologist Frederik Hendrickx (RBINS). ‘Cities filter species based on particular traits, like the ability to migrate and to tolerate higher temperatures. That is why you come across the same few species in every urban area, even in a forest within the city, where you would expect the same composition as in a forest in the countryside. It is not unlikely that similar mechanisms affect other insect species, and even plants.’
The study was published in Global Change Biology, and is one of the first to demonstrate this trait-filtering effect on such an extensive scale. These insights are important for measuring long-term effects for ecosystems and being able to anticipate them.