Land-use components, abundance of predatory arthropods, and vegetation height affect predation rates in grasslands

Land use is a major driver of biodiversity loss in many taxa including the mega-diverse arthropods, but consequences for arthropod-mediated processes are still little understood. Using a rapid ecosystem function assessment (REFA), we approximated predation by quantifying predation attempts on artificial sentinel prey. Dummies were placed on the soil surface of 83 managed temperate grasslands across a broad range of land-use intensities (grazing intensity, mowing frequency, and the amount of applied fertiliser) in two regions of Germany. Additionally, we measured vegetation height and assessed the abundance of ground-dwelling arthropods using pitfall traps. We documented predation marks left by arthropods, rodents, and birds. The proportion of dummies with predation marks (i.e. predation rates) differed between regions. Vegetation height was the strongest predictor for predation in our study but correlated only weakly with land use. Predation rates increased with increasing vegetation height, for rodents and for all predator groups combined. All three land-use components affected predation, which was most prominent for arthropod predation. Arthropod predation increased with higher grazing intensity and decreased with higher mowing frequency and higher fertilisation intensity. Also, the abundances of ground-dwelling arthropods affected predation. While predation rates generally increased with a higher abundance of carabids and decreased with higher abundance of ants, the effects of spider abundance interacted with region. Our results demonstrate that different components of land use can have counteracting effects on predation rates acting together with changes in the abundance of different predator groups and vegetation height. This suggests that land-use practices that sustain high vegetation and ground-dwelling predator abundances increase predation rates in grasslands and consequently the potential to provide ecosystem services in the form of pest control.