Data from: Urbanization-driven changes in web-building and body size in an orb-web spider

1. In animals, behavioural responses may play an important role in
determining population persistence in the face of environmental changes.
Body size is a key trait central to many life history traits and
behaviours. Correlations with body size may constrain behavioural
variation in response to environmental changes, especially when size
itself is influenced by environmental conditions. 2. Urbanization is an
important human-induced rapid environmental change that imposes multiple
selection pressures on both body size and (size-constrained) behaviour.
How these combine to shape behavioural responses of urban-dwelling species
is unclear. 3. Using web-building, an easily quantifiable behaviour linked
to body size, and the garden spider Araneus diadematus as a model, we
evaluated direct behavioural responses to urbanization and body size
constraints across a network of 63 selected populations differing in
urbanization intensity. We additionally studied urbanization at two
spatial scales to account for some environmental pressures varying across
scales and to obtain first qualitative insights about the role of
plasticity and genetic selection. 4. Spiders were smaller in highly
urbanized sites (local scale only), in line with expectations based on
reduced prey biomass availability and the Urban Heat Island effect. Web
surface and mesh width decreased with urbanization at the local scale,
while web surface also increased with urbanization at the landscape scale.
The latter two responses are expected to compensate, at least in part, for
reduced prey biomass availability in cities. The use of multivariate mixed
modelling reveals that although web traits and body size are correlated
within populations, behavioural responses to urbanization do not appear to
be constrained by size: there is no evidence of size-web correlations
among populations or among landscapes, and web traits appear independent
from each other. 5. Our results demonstrate that responses in
size-dependent behaviours may be decoupled from size changes, thereby
allowing fitness maximisation in novel environments. The spatial scale at
which traits respond suggests contributions of both genetic adaptation
(for web investment) and plasticity (for mesh width). Although fecundity
decreased with local-scale urbanization, Araneus diadematus abundances
were similar across urbanization gradients; behavioural responses thus
appear overall successful at the population level.