Increasing landscape complexity enhances species richness of farmland arthropods, agri-environment schemes also abundance – A meta-analysis

Intensification of agricultural production and simplification of landscape structure have negatively affected arthropod communities, in particular since the end of Second World War. Agri-environment schemes may partly compensate for these losses and enhance arthropod populations, but their effectiveness is higher in simple landscapes rather than complex landscapes, characterized by a large proportion and diversity of semi-natural areas. As the landscape-scale species pool is known to drive local species richness, we tested our hypothesis that landscape complexity determines local arthropod species richness, whereas local management affects only arthropod abundance. Here we undertake a meta-analysis as part of a wider systematic review of the effects of land use heterogeneity on arthropod species richness. We searched for studies quantifying the effects of agri-environment schemes (e.g. wildflower strips/areas, grassy field margins, organic farming) and landscape complexity on arthropod richness and abundance. We additionally separated vegetation- vs. ground-dwelling taxa, because the effects were hypothesized to be greater in the more mobile vegetation-dwelling taxa. As expected, increasing landscape complexity enhanced arthropod richness, but not their abundance. Unexpectedly, agri-environment schemes did not only support the abundance of arthropods, but also their species richness. This pattern was driven by the vegetation-dwelling, not the ground-dwelling taxa, presumably because the higher mobility of vegetation-dwelling taxa allows faster responses to environmental changes. Our results show that agri-environment schemes in Europe benefit both arthropod abundance and species richness, whereas increasing landscape complexity primarily enhances species richness. This is why both local and landscape management need to be taken into account to halt current biodiversity losses in agricultural landscapes. Agri-environment schemes need to be implemented at a larger spatial and temporal scales to enhance landscape complexity, maintaining or restoring biodiversity sustainably