Body-size shifts in aquatic and terrestrial urban
*, Caroline Souffreau
, Aurélien Kaiser
, Lisa F. Baardsen
, Thierry Backeljau
, Dries Bonte
, Kristien I.
, Marie Cours
, Maxime Dahirel
, Nicolas Debortoli
, Katrien De Wolf
, Jessie M. T. Engelen
, Diego Fontaneto
, Lynn Govaert
, Frederik Hendrickx
, Janet Higuti
, Luc Lens
, Koen Martens
, Hans Matheve
, Elena Piano
, Rose Sablon
, Isa Schön
, Karine Van Doninck
, Luc De Meester
& Hans Van Dyck
Body size is intrinsically linked to metabolic rate and life-history
traits, and is a crucial determinant of food webs and community
. The increased temperatures associated with the
urban-heat-island effect result in increased metabolic costs
and are expected to drive shifts to smaller body sizes
environments are, however, also characterized by substantial
, which favours mobile species. Here,
using a replicated, spatially nested sampling design across ten
animal taxonomic groups, we show that urban communities
generally consist of smaller species. In addition, although we
show urban warming for three habitat types and associated
reduced community-weighted mean body sizes for four taxa,
three taxa display a shift to larger species along the urbanization
gradients. Our results show that the general trend towards
smaller-sized species is overruled by filtering for larger species
when there is positive covariation between size and dispersal,
a process that can mitigate the low connectivity of ecological
resources in urban settings
. We thus demonstrate that the
urban-heat-island effect and urban habitat fragmentation are
associated with contrasting community-level shifts in body
size that critically depend on the association between body size
and dispersal. Because body size determines the structure and
dynamics of ecological networks
, such shifts may affect urban
Body size is a fundamental species trait relating to space use and
key life-history features such as longevity and fecundity
. It also drives
interspecific relationships, thus affecting ecological network dynam-
. Size-biased species loss has profound effects on ecosystem func-
. Ectotherms rely on ambient conditions to achieve operational
. Because higher ambient temperature increases
metabolic rates and the associated costs for a given body size
climatic warming is expected to drive shifts to communities consisting
of smaller species
Our planet is urbanizing quickly
, which is a primary example of
human-induced rapid environmental change. Cities are urban heat
islands characterized by increased temperatures that are decades ahead
of global averages
. Not only are cities warmer than surrounding areas,
but they also experience extensive fragmentation of (semi-)natural hab-
itats, and both of these effects increase with percentage built-up cover
(BUC; a proxy for urbanization)
. This provides an opportunity to
study the opposing effects of size-dependent thermal tolerance and
dispersal capacity, as larger body size favours dispersal in some, but
not all, taxa.
Here we test the hypothesis that urbanization causes shifts in com-
munity-level body size, and that these shifts are dictated by the commu-
nity-specific association between body size and dispersal. We generally
expect the urban-heat-island effect to drive shifts to species with
smaller body sizes in communities of ectothermic species, in line with
Atkinson’s temperature–size rule
. For taxa characterized by a positive
association between body size and dispersal, however, we also expect a
filtering in favour of larger-bodied species associated with habitat frag-
. Filtering for increased mobility has been demonstrated
for urban ground beetle and plant communities
. Hence, for taxa
characterized by a positive body-size–dispersal link, we predict that
the general community-level pattern of smaller species with increasing
urbanization may be neutralized or even reversed.
To test our hypothesis, we engaged in an analysis of community-level
shifts in body size across a broad range of both terrestrial and aquatic
taxa along the same systematically sampled urbanization gradients. We
studied the direction of change of community-level body size in ten
taxa using a replicated, highly standardized and nested sampling design
that covers urbanization gradients at seven spatial scales (50–3,200 m
radii; Fig. 1). We sampled each taxon at up to 81 sites, sampling 95,001
individuals from 702 species, with species-specific body size varying by
a factor of 400 (0.2–80 mm; Extended Data Table 1). Three of the ten
groups are characterized by a positive association between body size
and dispersal capacity (see Extended Data Table 1).
We show that the local temperature of pond, grassland and wood-
land habitats significantly increases with urbanization (linear mixed
regression models, P < 0.002; Extended Data Table 2). The intensity
of these urban-heat-island effects is consistently larger during night
and summer, in accordance with slower night-time city cooling and
higher irradiation levels in summer
(Fig. 2, Extended Data Fig. 1,
Extended Data Table 2). We also show that increased urbanization is
linked to significant declines in habitat amount and the patch size of
terrestrial habitats, and significant increases in distances among patches
for both terrestrial and aquatic habitats (Pearson’s r correlations, P ≤
0.020; Extended Data Fig. 2).
Confirming our metabolism-based prediction that interspecific
mean body size decreases with increasing temperature, urban com-
munities for four out of the seven taxa (ground spiders, ground beetles,
weevils and cladocerans) that did not have a positive size–dispersal
link display reduced community-weighted mean body size (CWMBS).
For ostracods, bdelloid rotifers and web spiders, no relationship with
urbanization is found. By contrast, all three taxa with positive size–
dispersal links display increased CWMBS in response to urbanization
Behavioural Ecology and Conservation Group, Biodiversity Research Centre, Earth and Life Institute, Université catholique de Louvain, Louvain-la-Neuve, Belgium.
Laboratory of Aquatic Ecology,
Evolution and Conservation, KU Leuven, Leuven, Belgium.
Evolutionary Ecology Group, University of Antwerp, Antwerp, Belgium.
Directorate Taxonomy and Phylogeny, Royal Belgian Institute of
Natural Sciences, Brussels, Belgium.
Terrestrial Ecology Unit, Biology Department, Ghent University, Ghent, Belgium.
Directorate Natural Environment, Royal Belgian Institute of Natural Sciences,
ECOBIO (Ecosystèmes, biodiversité, évolution), CNRS, Université de Rennes, Rennes, France.
Laboratory of Evolutionary Genetics and Ecology, URBE, NAXYS, University
of Namur, Namur, Belgium.
National Research Council, Institute of Ecosystem Study, Verbania-Pallanza, Italy.
German Centre for Integrative Biodiversity Research (iDiv), Halle-Jena-Leipzig,
Helmholtz Centre for Environmental Research (UFZ), Department of Community Ecology, Halle, Germany.
Centre of Research in Limnology, Ichthyology and Aquaculture/PEA, State
University of Maringá, Maringá, Brazil.
Limnology Research Unit, Biology Department, Ghent University, Ghent, Belgium.
Department of Life Sciences and Systems Biology, University of Turin,
Zoology Research Group, University of Hasselt, Hasselt, Belgium.
These authors jointly supervised this work: Luc De Meester, Hans Van Dyck. *e-mail: firstname.lastname@example.org
7 JUNE 2018 | VOL 558 | NATURE | 113
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