Urbanization Affects Animal Body Size



Urbanization puts a great selection pressure on species and could disrupt ecosystems. (Photo: RBINS)
Urbanization Affects Animal Body Size
post by
Reinout Verbeke

Animals in cities are considerably smaller or larger than species on the countryside, a large study concludes. Co-author Frederik Hendrickx (RBINS): ‘Urbanization puts a great selection pressure on species and could disrupt ecosystems.’

Biologists from – among others – UCL, KU Leuven, UGent and our Institute found out that for most animal groups species are remarkably smaller or larger in cities than in rural areas. They report about this finding in Nature.

Over the last five years, the researchers sampled ten animal groups – from beetles to water fleas – on 81 sites in Flanders and Brussels, for a total of 95.000 specimens from 702 species. For most organism groups, species in cities were on average smaller – even up to 16% - than those in rural areas. Butterflies, moths and grasshoppers showed an opposite pattern: they were on average considerably larger than in rural areas.

More Heat and Less Green

The shift towards smaller species in urban regions is likely attributed to the ‘heat island effect’. Cities are hotter than rural areas, because buildings absorb heath and release it during colder periods’, biologist Isa Schön (RBINS) explains. ‘In ponds, grasslands and woodlots within urban settings, we record higher ambient temperatures. This heat island effect selects for smaller species, because they are better suited to deal with increased metabolism in warmer environments.’

On the other hand, some groups in urbanized areas prove to be larger, because habitats are more fragmented and that selects for mobile species. ‘Larger grasshoppers or butterflies are usually more mobile and are generally more successful in reaching a new habitat’, Frederik Hendrickx says. ‘Cities are not a hostile environment for fauna, and exerts a great selection pressure on their mobility and heat resistance. In this way, ecological relations between species may change.’ An example: in cities, only the smaller water fleas thrive. They digest less algae than larger water fleas, which on its turn may induce local algal blooms.

City Planners to the Rescue

The study opens up possibilities for new research into long-term effects of urbanization on ecosystems. Hans Van Dyck (UCL): 'Such insights will be essential to design cities that show less strong effects on biodiversity. Urban planners could create and amend urban ponds and green infrastructure to increase the amount and quality of habitats.'



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