Urban biodiversity: the importance of scale

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While much is known about the scaling of biodiversity, less is known about specifically how biodiversity scales in urban areas. This is an important question because over two-thirds of humans live in urban areas. Understanding how, precisely, biodiversity scales in urban areas will inform management. Linear relationships would imply that similar interventions should work across the range of city sizes (from small towns to the largest mega-cities) whereas non-linear relationships would imply that biodiversity strategies must be tailored to the size of the city. We focused on avian biodiversity because more than half of the species are found in urban areas (6,120 out of 11,162 species), including at least 350 threatened ones. We calculated species richness in 2,568 cities and used eBird, a community science platform, to estimate species richness. After controlling for a variety of variables that might explain variation in avian biodiversity, we found a non-linear relationship in cities and contrasted this to a well-established power law found in natural areas. After controlling for other key variables that might explain variation in urban biodiversity, the log-log relationship between city area and avian biodiversity had a slope of 0.42 until cities got bigger than 331 km2, beyond which it decreased to 0.15. This suggests that unique processes affect urban biodiversity in smaller and larger cities. When we focused on the subset of threatened species, we found a linear relationship with a slope of 0.20. Urbanization not only contributes to a global extinction, but urban areas may provide important habitat for threatened species.

About speaker: Dr. Nannan Gao is a Postdoctoral associate with Daniel T. Blumstein in the Department of Ecology and Evolutionary Biology at UCLA. Her research mainly focuses on studying the relationship between urban biodiversity and city size by creating global urban biodiversity datasets that include small towns to megacities involving spatiotemporal advanced computing, statistical computing, and data science. Dr. Gao received her Ph.D. from the Chinese Academy of Science and also studied human geography and urban planning at Peking University. She seeks to balance humans and animals in urban areas.