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

• Applicant: Professorin Dr. Heike Feldhaar
• Subject Area: Ecology and Biodiversity of Animals and Ecosystems, Organismic Interactions ; Ecology of Land Use
• Term: from 2014 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 252153788

• Final Report Year: 2019

Final Report Abstract

The aim of the project AntAphid within the framework of the Biodiversity Exploratories was to estimate the impact of management intensity on ants along the land use gradient in temperate grasslands. While negative impacts of land use intensity on ants had been shown before in temperate and Mediterranean grasslands the effects of the different land use components mowing, grazing and fertilization have not been disentangled before. Ant species richness and ant abundance both decreased significantly with more intensive land use. In the project we were able to show that mowing is the most detrimental land use practice in grasslands in comparison to fertilization or grazing. Nest structures such as epigaeic nest mounds may get destroyed during the mowing process, affecting ants directly and negatively. As land use intensification may also alter nutritional resources such as potential trophobionts or prey items we expected that ants may also be indirectly affected by land use intensification. We had expected that carbohydrate sources such as honeydew collected from trophobionts or floral nectar resources should become scarcer with land use intensification as they may also be destroyed through mowing. As a result ants should feed on a higher trophic level. Results on the abundance of ant-aphid interactions corroborate this hypothesis as their frequency decreased significantly with increasing land use intensity. However, contrary to our expectation, the stable isotope analysis showed that the most abundant ant species tend to feed on a lower trophic level with increasing land use intensity. In a second part of the project that became feasible through the work by another PhD-student funded from other sources we studied the impact of forest management on ant communities in the forest plots of all three Exploratories. This project was in cooperation with the Arthropod Core project (Weisser et al.) where we obtained ant samples from pitfall traps from. While forest management had been shown to have an overall negative effect on ant communities in tropical, and a positive effect in boreal forests it was unclear how ant communities are affected by the different components of forest management. Main direct effects of forest management on ant abundance and species richness were caused by tree species selection, measured as dominant tree species. The main positive indirect effect was mediated by a reduced canopy cover with an increasing proportion of oak and pine, resulting in a higher temperature amplitude. Functional diversity of ant communities was also influenced by forest management. Similarly to ant species richness functional diversity increased in more open forests with lower structural complexity. Our results show that forest management practices in temperate forests strongly impact ant community structure.

Publications

• (2018) Effect of forest management on temperate ant communities. Ecosphere 9: e02303
  Grevé, M., J. Hager, W.W. Weisser, P. Schall, M.M. Gossner, H. Feldhaar
  
• (2019) Direct and indirect effects of land-use intensification on ant communities in temperate grasslands. Ecology and Evolution
  Heuss, L., M.E. Grevé, D. Schäfer, V. Busch, H. Feldhaar
  
• (2019) Land-use components, abundance of predatory arthropods, and vegetation height affect predation rates in grasslands. Agriculture, Ecosystems and Environment 270-271: 84-92
  Meyer, S.T., L. Heuss, H. Feldhaar, W.W. Weisser, M.M. Gossner