Small urban fragments maintain complex food webs of litter-dwelling arthropods in a subtropical city in China

Abstract

Urbanization-induced environmental changes such as habitat fragmentation impact arthropod assemblages and food web-related ecosystem functions, such as nutrient cycling and energy fluxes. Yet, we lack insight into how arthropod food webs are structured along urban fragmentation gradients. Here, we investigated the community composition and food web structure of litter-dwelling arthropods along fragmentation gradients (green median strip, i.e. green fragments in the middle of roads, urban park, urban forest and natural forest) in Xiamen City, southeast China. We found the density of litter-dwelling arthropods in median strips and urban parks to be two to four times higher than in urban and natural forests, with, as indicated by literature-based stable isotope values, 67%–68% of the individuals comprising primary consumers (trophic level I). Consequently, more complex food webs were found in small urban fragments (i.e., green median strip and urban park) than in the other fragments studied, including higher linkage density and higher energy flux. The biomass of litter on the floor was significantly correlated with the density of arthropods of trophic levels I, III and IV, and each trophic guild positively correlated with each other pointing to the dominance of bottom-up forces. Overall, our results suggest that small urban fragments maintain a high density of arthropods forming complex food webs and thereby may contribute to maintaining high energy fluxes and providing important ecosystem functions in urban areas.