Differential responses of ant assemblages (Hymenoptera: Formicidae) to long-term grassland management in Central Germany

Biodiversity decreases in response to either intensive management or land abandonment in permanent grasslands of Central Europe. Here, we evaluated the long-term impacts of different management regimes on ant richness, nest abundance, assemblage structure, and food resource use in three experimental grassland sites in Thuringia, Germany. Each experimental site comprised identical management regimes established in 2000 / 2001. Grassland sites differed with respect to plant community type and abiotic conditions. Ants were assessed in four treatments representing a gradient in management intensity: intensive mowing (four-five cuts per year), traditional mowing (two cuts per year), mulching (mulched once per year), and abandonment (no management). A total of fourteen species belonging to three genera were recorded. Overall, ant responses to management treatments were site dependent. Mean species richness did not vary across treatments but sites. Nest abundance was high in the intensive and traditional treatment but strikingly low in the mulching treatment. Assemblages were more diverse in the traditional and abandonment treatment in sites representing semi-dry conditions, while the intensive treatment enhanced ant diversity under mesic site conditions. Higher rates of food monopolization were detected in the intensive and traditional treatment in drier conditions. Our results show that long-term management affected ant assemblages in different ways, but these effects were strongly related to local climate and soil conditions. The responses of ants to grassland management, that is mowing, can be explained by how these management practices (or their absence) affect the microclimatic conditions under a local context. Hence, the interplay of these factors along with the species requirements is of key importance to determining the impact of the land management on ant assemblages in German and Central European grasslands.