Butterfly biodiversity in the city is driven by the interaction of the urban landscape and species traits: a call for contextualised management

Context Urbanisation is an environmental filter for many species that leads to community homogenisation, with a few species inhabiting isolated patches (e.g. public and private gardens and parks) embedded within the urban landscape. Promoting biodiversity in urban areas requires understanding which species traits allow species to survive the urban landscape. Objectives The objective of this study was to assess how species traits and landscape factors combine to allow species functional groups to live in the city. Methods We used butterfly count data collected by volunteers in 24 gardens of Barcelona city, during 2018 and 2019. Species were clustered in functional groups according to their traits. We applied a multinomial choice model to test for the effect of the landscape on the different functional groups. Results Three functional groups became prevalent in the city while a fourth, containing most sedentary specialist species, was filtered out. Although the observed groups had similar species richness, abundances varied depending on urban landscape characteristics. Specialist sedentary specialists and medium mobile species were all favoured by patch connectivity; while the presence of mobile generalist species was only enhanced by habitat quality. Our results indicate that butterfly communities are more diverse in highly connected gardens. Conclusions Our study highlights the need of contextualised management with actions accounting for the species functional groups, rather than a management focused on general species richness. It demonstrates that urban landscape planning must focus on improving connectivity inside the city in order to diversify the community composition.