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Abstract:
Intensive land use is a driving force for biodiversity decline in many ecosystems. In semi-natural grasslands, land-use
activities such as mowing, grazing and fertilization affect the diversity of plants and arthropods, but the combined effects of
different drivers and the chain of effects are largely unknown. In this study we used structural equation modelling to analyse
how the arthropod communities in managed grasslands respond to land use and whether these responses are mediated
through changes in resource diversity or resource quantity (biomass). Plants were considered resources for herbivores
which themselves were considered resources for predators. Plant and arthropod (herbivores and predators) communities
were sampled on 141 meadows, pastures and mown pastures within three regions in Germany in 2008 and 2009. Increasing
land-use intensity generally increased plant biomass and decreased plant diversity, mainly through increasing fertilization.
Herbivore diversity decreased together with plant diversity but showed no response to changes in plant biomass. Hence,
land-use effects on herbivore diversity were mediated through resource diversity rather than quantity. Land-use effects on
predator diversity were mediated by both herbivore diversity (resource diversity) and herbivore quantity (herbivore
biomass), but indirect effects through resource quantity were stronger. Our findings highlight the importance of assessing
both direct and indirect effects of land-use intensity and mode on different trophic levels. In addition to the overall effects,
there were subtle differences between the different regions, pointing to the importance of regional land-use specificities.
Our study underlines the commonly observed strong effect of grassland land use on biodiversity. It also highlights that
mechanistic approaches help us to understand how different land-use modes affect biodiversity.
