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

Abstract

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.

Insect ecology and conservation in urban areas: An overview of knowledge and needs

“…Urban density may also select for dispersal-enhancing morphologies within populations or species assemblages, which has been proposed for flight-related traits of aquatic beetles (Liao & Lin, 2024), as well as body size of wild bees (Brasil et al, 2023) and macro moths (Merckx, Kaiser, & Van Dyck, 2018). These patterns, which are also considered a form of ecological filtering, may reflect changes in the costs and benefits of dispersal in urban environments (Ancillotto & Rocco, 2024;Jones & Leather, 2012), although they may also reflect traits of founder individuals in low-dispersal systems, and conclusions are largely uncertain (see also genetics section below) (Federico et al, 2024).…”

“…Many works indicate a homogenisation and decrease in functional type, species diversity and/or insect abundance as urban density increases (in this SI see: Barao et al, 2024;Casanelles-Abella et al, 2024;Federico et al, 2024;Rivest & Kharouba, 2024;Sanetra et al, 2024;Svenningsen et al, 2024). This picture is, however, nuanced (e.g., Ancillotto & Rocco, 2024;Federico et al, 2024;Ombugadu et al, 2024) and although urban areas can detrimentally impact some insect taxa through the predominance of artificial environments, constrained habitats and disturbances, other taxa can adapt and thrive in the mosaic of semi-natural and novel environments, management variation and abundant resources (Curry et al, 2024;Hill et al, 2024;Nunes et al, 2024;Plummer et al, 2024;Xu et al, 2024).…”