Contrasting relationships between socio-economic status and avian ecosystem service provision in a developing world city

Urban biodiversity, and the ecosystem services it provides, are not equitably distributed across socio-economic gradients. Previous studies have highlighted disparities in alpha-diversity along socio-economic gradients, but few have translated those findings into differences in ecological function, and critically, ecosystem service delivery by urban wildlife along the same gradient. This study tested whether turnover in bird functional diversity, and associated avian ecosystem services, varied along the socio-economic gradient of a large developing world city. We surveyed bird diversity in 27 public access urban green spaces across the urban and socio-economic gradients in the city of Johannesburg, South Africa. Bird functional traits, representing cultural, regulation and supporting ecosystem services were assigned to species recorded during the surveys. A fourth-corner analysis revealed that socio-economic and urban landscape compositional variables surrounding the green spaces acted as filters of bird species' functional traits, suggesting differences in ecosystem service provision along development gradients. Urban green spaces in low-income landscapes supported more birds of 'public interest' (a cultural ecosystem service), but in contrast had fewer nectivores (a supporting ecosystem service - pollination). Tree cover had a positive relationship with frugivorous bird abundance, and green space size had a negative relationship with granivorous bird abundance (both supporting ecosystem services - seed dispersal). The contrasting relationships, particularly between socio-economic status and ecosystem service provision, suggest that it is important to interrogate how socio-economic variables affect access to urban biodiversity beyond commonly used metrics of alpha-diversity. This allows for nuanced perspectives of environmental injustice in cities and relevant interventions that can aid in circumventing it.

Automated summary

Urban biodiversity and its ecosystem services are distributed unevenly along socio-economic gradients. Socio-economic and urban landscape variables act as filters of bird species' functional traits, leading to differences in ecosystem service provision. However, urban green spaces in low-income areas support more birds of public interest but fewer birds that provide supporting ecosystem services. Tree cover and green space size have differing relationships with bird functional traits.