Urban effects on saprophagous macroarthropods are mainly driven by climate: A global meta-analysis

Abstract

Macrodecomposers provide important ecosystem services even in human dominated habitats including urban ecosystems, but the effect of urban land conversion on their species diversity and abundance has not been explored at global scale. Here, we present the first meta-analysis to quantify the general response of two major arthropod taxa, terrestrial isopods and millipedes to urbanization and to reveal the underlying mechanisms. Climatic (temperature, precipitation, growing season length), edaphic (pH, organic carbon, CaCO3 and clay content of surface soils), urban (population density, city age, vegetation cover and mean actual evapotranspiration) parameters and methods of study (duration, sampling technique, replications) were used as moderators. We used a hierarchical meta-analytic approach to consider the dependence of multiple effect sizes obtained from one study. Altogether 156 paired observations were extracted from 59 urban studies conducted between 1980 and 2020. Urbanization had a negative effect on species diversity (species richness and Shannon index) of both macroarthropod taxa. However, both the direction and strength of their abundance response varied to a greater extent, resulting in a neutral effect of urban disturbance on them. The key drivers influencing the urban effects on macroarthropods were mean annual temperature and precipitation, absolute minimum temperature and length of growing season. The study also highlighted the importance of sampling methods: direct sampling (hand collecting) resulted in stronger urban effects presumably due to several sources of sampling bias. Our global synthesis highlighted that urbanization is a threat to soil arthropods, particularly to litter-dwelling detritivores, which potentially alters plant residue processing and ultimately soil biogeochemical cycles.