Large uncertainty in trait responses across insects among overall declines in a subtropical city

Continued and rapid development of urban environments presents many challenges to organisms living in and around cities. Insects are among the most abundant and diverse class of animals but surprisingly little is known about how most species respond to urbanisation across clades with varying life histories, especially in the subtropics and tropics.

In this study, we sample insect abundance and diversity across an urbanisation gradient in a subtropical region to assess the impact of urbanisation on 43 phototactic species of insects representing eight distinct orders. We also attempted to determine which life history traits best explain how species respond to urbanisation.

We predicted an overall loss of abundance and richness with increasing urbanisation, with smaller, generalist species being the least impacted. We also predicted that species with above ground larval habitats would be less affected by urbanisation.

Overall, urban development decreased both species richness and the abundance of individuals per order, with abundance being most reduced for Hymenoptera but least reduced for Coleoptera. At a species‐specific level, urban development negatively impacted most but not all species, although uncertainty around these estimates was high. We did not identify key traits that determined a species' sensitivity to urbanisation.

Our results showcase that urbanisation may impact ecosystem function given overall reduction in the number of individual insects per order, despite wide variability in species‐specific responses. Our study also emphasises the importance of species selection when designing studies that examine responses of multiple taxa across an environmental gradient.