Taxonomic and functional homogenization of farmland birds along an urbanization gradient in a tropical megacity

Urbanization is a major driver of land use change and biodiversity
decline. While most of the ongoing and future urbanization hot spots are
located in the Global South, the impact of urban expansion on agricultural
biodiversity and associated functions and services in these regions has
widely been neglected. Additionally, most studies assess biodiversity
responses at local scale (α-diversity), however, ecosystem functioning is
strongly determined by compositional and functional turnover of
communities (β-diversity) at regional scales. We investigated taxonomic
and functional β-diversity of farmland birds across three seasons on 36
vegetable farms spread along a continuous urbanization gradient in
Bangalore, a South Indian megacity. Increasing amount of grey area in the
farm surroundings was the dominant driver affecting β-diversity and
resulting in taxonomic and functional homogenization of farmland bird
communities. Functional diversity losses were higher than expected from
species declines (i.e. urbanization acts as an environmental filter), with
particular losses of functionally important groups such as insectivores of
crop pests. Moreover, urbanization reduced functional redundancy of bird
communities, which may further weaken ecosystems resilience to future
perturbations. Our study underscores urbanization as a major driver of
taxonomic and functional homogenization of species communities in
agricultural systems, potentially threatening crucial ecosystem services
for food production.