Little evidence for land-use filters on intraspecific trait variation in three arthropod groups

Abstract. Declines in species richness and abundance of insects over the last decades are often driven by anthropogenic land use and can have severe consequences for ecosystem functioning. Many studies investigated the effects of land-use intensification on the distribution of phenotypic traits across species at the community level, often with mixed results. However, biotic and abiotic environmental filters and potential selection act on individuals within each species, i.e., at the species' population level, and thus drive the extent of intraspecific phenotypic variation. Here, we compare the morphological trait variation within selected species of dung beetles, bees and grasshoppers and link this variation to land-use intensity in forests and grasslands. Selected traits included absolute body size measures and relative leg, wing or eye size, or shape and are often interpreted as “functional traits” in the context of specific ecological responses or effects. We predicted that trait variability among individuals of arthropod species is reduced in intensively used ecosystems (with pronounced environmental filtering) compared to low-intensity ones, particularly for arthropod species that were more abundant in intensively used sites (“land-use winners” compared to “losers”). In general, only few effects of land-use intensity on trait variation were found showing a decreasing variation with increasing land-use intensity in forests but an increasing variation in grasslands. Although many studies confirmed strong land-use impacts on species composition, diversity and trait distribution, including evidence from the same land-use gradients, we were not able to confirm consistent effects at the intraspecific level. However, the choice of which traits are included in analyses and the linkage between phenotypic variation and genetic variability can strongly influence the conclusions drawn on ecological processes. Therefore, we suggest extending the use of intraspecific trait variation on other, more specific response or effect traits and a broader range of species in future studies.