Only habitat specialists become smaller with advancing urbanization

Abstract

AbstractAimUrbanization profoundly changes environments, ecosystems and biodiversity. The urban heat island (UHI) effect represents one of the most consistent human‐induced environmental change in urbanized areas. Recently, it was observed that the UHI causes community‐wide shifts towards species with smaller body sizes in urban communities of ectotherms due to increased metabolic costs. We here assembled a large dataset of published data of geographically distant carabid communities collected along urbanization gradients to examine whether we could confirm this consistent change in body size distribution.LocationRural and urban forests at 11 northern temperate locations, spanning 25 latitudinal degrees.Time period2002–2018.Major taxa studiedSpecies of ground beetles (Coleoptera: Carabidae).MethodsWe evaluated size distribution changes using community‐weighted mean body sizes of ground beetles collected from similarly vegetated rural and urban habitats between 2002 and 2018. We separately examined the UHI effect on the various sub‐assemblages of the carabid community.ResultsWhen analysing the entire dataset, we could not detect any clear trend in the community body size mean, with urban communities showing similar values to those sampled in rural areas. However, the sub‐assemblage of forest habitat specialists consistently displayed a significant shift towards smaller species from rural to urban habitats. The inconsistent trend at the community level was likely due to the influx into urban habitat fragments of non‐specialist species. The UHI effect also had a significant influence but only on the forest specialist sub‐assemblage.Main conclusionsOur results indicated that forest‐specialist species were most affected by the UHI as a powerful urbanization‐related environmental filter, whereas this effect was not evident for the overall community. Urban management practices should aim to minimize the intensity of urbanization‐related environmental filters such as the UHI, to enable habitat specialists to survive in habitat fragments under urbanized conditions.