Interactive effects of vegetation and soil determine the composition and diversity of carabid and tenebrionid functional groups in an arid ecosystem

• We assessed interactive effects of vegetation and soil changes on communities of detritivorous, herbivorous, and predatory beetles.
• Vegetation–soil interactions explained most of the composition variation in functional groups than did vegetation or soil alone.
• Vegetation changes affected the composition of beetle functional groups more than soil changes.
• Changes in vegetation and soil affected beetle abundance and diversity through both direct and indirect effects.

The community dynamics of ground beetles as a dominant group in arid ecosystems are strongly affected by land-use change associated alterations in vegetation and soil conditions. However, little is known about the relative effects of altered vegetation and soil, or their interactions, on the composition and diversity of beetle functional groups. To address this question, we collected data on the species richness and activity abundance of ground carabid and tenebrionid beetle functional groups (predators, herbivores, and detritivores), along a gradient of land-use conversion from natural grassland to pure and mixed plantations of two shrub species (Haloxylon ammodendron and Tamarix ramosissima) in an arid region of northwestern China. Additionally, we collected key variables related to the vegetation (shrub cover, height, herbaceous plant biomass, and species richness) and soil (soil pH, texture, and salinity). Variation partitioning showed that vegetation changes had stronger effects on the functional group composition than changes in the soil did. However, vegetation–soil interactions explained more of the composition variation in the beetle functional groups than vegetation or soil alone. Shrub cover and herbaceous species richness were the best predictors of species composition of detritivores and herbivores. For predator species composition, shrub height and cover were the best predictors. Structural equation models showed that changes in vegetation and soil influenced beetle abundance and diversity through both direct and indirect effects, and the strength of this influence varied among the functional groups. Overall, we conclude that vegetation and vegetation–soil interactions are important determinants of beetle community assemblies.