Urban warming alters body size in Neotropical geometrid moths: Divergent patterns at community and intraspecific scales

Abstract Urbanization is a global phenomenon inducing rapid and permanent land‐use changes. These transformations have significant impacts on biodiversity and ecosystem functioning, primarily through the filtering of specific functional and/or morphological traits. In animals, body size is a critical functional trait linked to ecosystem functioning because it affects metabolism, dispersal and trophic interactions. Moth communities are particularly sensitive to urbanization, often exhibiting reduced species diversity due to non‐random species loss. However, body size responses to urbanization remain ambiguous, as contrasting eco‐evolutionary processes may drive shifts in opposite directions. The Urban‐Heat‐Island effect (UHI) predicts a reduction in body size—following Atkinson's temperature‐size rule—due to increased metabolic costs, whereas habitat fragmentation may favour larger individuals with greater dispersal ability. Here, to test these hypotheses, we sampled geometrid moths along an urbanization gradient in a tropical Andean city and analysed body size variation at both community and population levels in relation to UHI intensity. At the community level, our results revealed a reduction in body size at high levels of UHI, consistent with the temperature‐size rule. However, at the population level, phenotypic changes were consistent with opposing pressures associated with urban warming and habitat fragmentation, depending on the species. Hence, our study suggests that urban environments can filter species idiosyncratically within communities and individuals within species, but through different mechanisms.