Direct and indirect effects of land use intensification on ant communities in temperate grasslands

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Ants are important ecosystem engineers in temperate grasslands as they modify soil structure and microbial communities by building subterranean nests and importing resources into these nests. Intensification of land use has been shown to negatively influence the structure of ant communities by reducing ant species richness and abundance with potential consequences for their functions as soil engineers. However, the mechanisms leading to changes in community structure are not well understood. Different types of land use may affect composition of ant communities and overall ant abundance either by altering available food sources (indirect effects) or by disturbance of nesting sites (direct effects). Ant communities in grasslands usually comprise species that consume prey, scavenge or feed on plant-derived food sources via trophobiosis (e.g. with aphids ), or rely on several of these food sources. Intensified land use typically results in lower plant species richness, which in concert with more frequent mowing may result in lower trophobiont abundance above as well as below-ground, while potential prey items (e.g. generalisitc herbivores) may be less affected. Omnivorous ant species may therefore show a shift in trophic niche towards relatively more predation. If such trophic plasticity is limited, the community may comprise a different set of species and show a shift towards more predacious species. Both mechanisms result in an ant community feeding on a higher trophic level. Ants should also be affected directly by more intensive land use due to disturbance of nesting sites by mowing and heavy grazing. Mound-building species should be more strongly affected by disturbances than other species. Ant as well as trophobiont species richness and abundance will be measured above and belowground on all grassland plots and interactions among the groups documented. The trophic niche of ants will be assessed using stable isotope analyses as well as preferred nutrient intake in the field. Mechanisms of community assembly will be analyzed by combining co-occurrence patterns with phylogenetic and phenotypic data. Potential changes in the specificity of trophic interactions between ants and aphids will be assessed using network analyses.