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

Declines in species richness and abundance of insects over the last decadesare often driven by anthropogenic land use and can have severe consequencesfor 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 intensivelyused ecosystems (with pronounced environmental filtering) compared tolow-intensity ones, particularly for arthropod species that were moreabundant in intensively used sites (land-use winners compared tolosers). In general, only few effects of land-use intensity on traitvariation were found showing a decreasing variation with increasing land-useintensity in forests but an increasing variation in grasslands. Althoughmany studies confirmed strong land-use impacts on species composition,diversity and trait distribution, including evidence from the same land-usegradients, we were not able to confirm consistent effects at theintraspecific level. However, the choice of which traits are included inanalyses and the linkage between phenotypic variation and geneticvariability can strongly influence the conclusions drawn on ecologicalprocesses. Therefore, we suggest extending the use of intraspecific traitvariation on other, more specific response or effect traits and a broaderrange of species in future studies.

Automated summary

Declines in insect species richness and abundance are often caused by human activities and can have significant impacts on ecosystem functioning. Many studies have examined the effects of land-use intensity on phenotypic trait distribution among species at the community level, but results have been mixed. This study investigates intraspecific variation in morphological traits within selected species of dung beetles, bees, and grasshoppers and links it to land-use intensity in forests and grasslands.