Acknowledgements
We thank Annika Ackermann and the Grassland Sciences group at ETH Zürich for the help with the CN -analyses, Matthias Saurer and Loïc Schneider at WSL for the help with the isotope analyses, Saran Karadaghi, Marc-Jacques Mächler, Sandra Racine, Evelin Iseli and and Annette Bieger Altermatt for the help in the field and the lab, and the Genetic Diversity Center at ETH for the use of laboratory facilities. This research was funded by ETH Zurich and the Swiss National Science Foundation grant 31003A_173210. JMA received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement no. 678841.