Data from: Urbanisation-driven homogenisation is more pronounced and happens at wider spatial scales in nocturnal and mobile flying insects

Aim We test whether urbanisation drives biotic homogenisation. We
hypothesise that declines in abundance and species diversity of aerial
insects are exacerbated by the urbanisation-driven loss of species with
low habitat generalism, mobility and warm-adaptedness. We predict this
homogenisation to be more pronounced for nocturnal taxa, and at wider
scales for mobile taxa. Location Belgium Time period Summers 2014-2015
Major taxa studied Lepidoptera Methods We compare communities along
urbanisation gradients using a shared, replicated and nested sampling
design, in which butterflies were counted within 81 grassland and
macro-moths light-trapped in 12 woodland sites. We quantify taxonomic and
functional community composition, the latter via community-weighted means
and variation of species-specific traits related to specialisation,
mobility and thermophily. Using linear regression models, variables are
analysed in relation to site-specific urbanisation values quantified at
seven scales (50-3200 m radii). At best-fitting scales, we test for
taxonomic homogenisation. Results With increasing urbanisation, abundance,
species richness and Shannon diversity severely declined, with butterfly
and macro-moth declines due to local- versus landscape-scale urbanisation
(200 vs. 800-3200 m radii, respectively). While taxonomic homogenisation
was absent for butterflies, urban macro-moth communities displayed higher
nestedness than non-urban communities. Overall, communities showed mean
shifts towards generalist, mobile and thermophilous species, displaying
trait convergence too. These functional trait models consistently fit best
with urbanisation quantified at local scales (100-200 m radii) for
butterfly communities, and at local to wider landscape scales (200-800 m
radii) for macro-moth communities. Main conclusions Urban communities
display functional homogenisation which follows urbanisation at scales
linked to taxon-specific mobility. Light pollution may explain why
homogenisation was more pronounced for the nocturnal taxon. We discuss
that urbanisation is likely to impact flying insect communities across the
globe, but also that impacts on their ecosystem functions and services
could be mitigated via multi-scale implementation of urban green
infrastructure.