The effect of grain size on the relationship between urbanization and bird diversity

Abstract

The intensifying urbanization markedly influences bird diversity, frequently with negative repercussions but also yielding mixed outcomes. Our hypothesis posits that the variability in results often arises from methodological choices in measuring both bird diversity and urbanization. We investigated whether the effects of urbanization on bird diversity are influenced by the grain size of the measurements. Selected urban areas in China from 2000 to 2020 were analyzed, and bird diversity distributions were derived from citizen science data. Urbanization levels rose by approximately 30%, resulting in the loss of around 17 urban bird species. Panel data analyses at different grain sizes showed that urbanization negatively affected bird diversity, while taxonomic diversity was more resilient at the grain size (1–10 km). Furthermore, our findings indicate a grain effect on the urbanization-bird diversity relationship, revealing instability at various measurement grains. Functional diversity requires finer grains (1 km), reflecting feature redundancy. Our analytical approach enhances understanding of the mechanisms and cross-grain relationships through which urbanization impacts bird communities, and underscores the significance of grain in urban ecology.