Body-size shifts in aquatic and terrestrial urban communities

Abstract

Body size is intrinsically linked to metabolic rate and life-history traits, and is a crucial determinant of food webs and community dynamics. 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 . Urban environments are, however, also characterized by substantial habitat fragmentation , 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 ecosystem function.

Urbanization‐driven homogenization is more pronounced and happens at wider spatial scales in nocturnal and mobile flying insects

“…The pattern of dominance of mobile species with increasing urbanization is a result fully in line with recent findings on body‐size shifts due to urbanization (Merckx, Souffreau, et al, ). This multi‐taxa study showed that butterfly and macro‐moth communities become increasingly dominated by larger species with urbanization.…”

“…The body‐size shift was interpreted as a shift towards increased mobility since body size is positively linked to mobility in Lepidoptera (Nieminen et al, ; Sekar, ; Slade et al, ; Stevens, Trochet, Van Dyck, Clobert, & Baguette, ). Rather than by the UHI‐effect, which would have caused shifts towards smaller body size for metabolic reasons (Merckx, Souffreau, et al, ), the body size of the urban communities of butterflies and moths appeared instead to be shaped mainly by the high degree of habitat fragmentation. It is obvious that the typically severe fragmentation of ecological resources in urban settings constitutes an effective filter on mobility, so that mainly the more mobile species are retained within urban communities (Sattler et al, ).…”

“…Not only are towns and cities typified by extensive loss and fragmentation of (semi)natural habitats, they are also characterized by higher ambient temperatures [i.e., the urban‐heat‐island (UHI) effect] and higher levels of artificial light at night (ALAN) than surrounding rural and natural areas (Parris, ). These effects of habitat fragmentation, UHI, and ALAN get stronger with increasing built‐up cover (BUC) (Merckx, Souffreau, et al, ; Sutton, ).…”

Responses of zooplankton body size and community trophic structure to temperature change in a subtropical reservoir

“…We found shrinking body size with elevated temperature along time series from the mixing to stratification periods. The smaller zooplankton taxonomic groups found in the stratification period were in line with recent investigations that warming benefits smaller organisms (Chiba et al, ; Merckx et al, ; Yvon‐Durocher et al, ). We also found that taxonomic groups differed in their body size response to temperature, which might be due to different food adaptability and competitive ability (Hart & Bychek, ; Sheridan & Bickford, ).…”

The origin of urban communities: From the regional species pool to community assemblages in city

“…Knapp et al, ) and overall suggest that local climatic conditions, and resource availability and distribution are the main drivers of the assembly of urban communities from the regional pool. For instance in a meta‐analysis, Merckx et al () find body size changes among several taxa, possibly driven by both the urban‐heat‐island effect and habitat fragmentation. Similarly, our model city may select for cavity‐nesting bees because of the increasing availability of artificial cavities but also the corresponding lack of bare ground for ground nesting bees.…”