Abstract
Good knowledge on how increasing urbanization affects biodiversity is essential in order to preserve biodiversity in urban green spaces. We examined how urban development affects species richness and total abundance of butterflies as well as the occurrence and abundance of individual species within the Helsinki metropolitan area in Northern Europe. Repeated butterfly counts in 167 separate 1-km-long transects within Helsinki covered the entire urbanization gradient, quantified by human population density and the proportion of built-up area (within a 50-m buffer surrounding each butterfly transect). We found consistently negative effects of both human population density and built-up area on all studied butterfly variables, though butterflies responded markedly more negatively to increasing human population density than to built-up area. Responses in butterfly species richness and total abundance showed higher variability in relation to proportion of built-up area than to human density, especially in areas of high human density. Increasing human density negatively affected both the abundance and the occurrence of 47% of the 19 most abundant species, whereas, for the proportion of built-up area, the corresponding percentages were 32% and 32%, respectively. Species with high habitat specificity and low mobility showed higher sensitivity to urbanization (especially high human population density) than habitat generalists and mobile species that dominated the urban butterfly communities. Our results suggest that human population density provides a better indicator of urbanization effects on butterflies compared to the proportion of built-up area. The generality of this finding should be verified in other contexts and taxonomic groups.
Highlights
IntroductionWith an increasing proportion of the global human population living in cities (United Nations 2018), the preservation of urban biodiversity has become recognized as an important policy target which positively affects the well-being of people living in urban areas (Fuller et al 2007; Dallimer et al 2012; Aronson et al 2017)
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Correlations between the urbanization measures and butterfly species richness and total abundance were strongest within the 50-m buffer (Fig. 2), and this buffer width was selected for the main statistical analyses
Summary
With an increasing proportion of the global human population living in cities (United Nations 2018), the preservation of urban biodiversity has become recognized as an important policy target which positively affects the well-being of people living in urban areas (Fuller et al 2007; Dallimer et al 2012; Aronson et al 2017). Many studies have demonstrated that species richness tends to decline with increasing urbanization, the responses differ between taxonomic groups as well as between species within taxonomic groups (McKinney 2008; Aronson et al 2014; Ives et al 2016; Piano et al 2020). A high diversity of pollinating insects such as bees has
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