Duplicate title to Brännström, Å., Gross, T., Blasius, B., & Dieckmann, U. ORCID: https://orcid.org/0000-0001-7089-0393 (2010). Consequences of fluctuating group size for the evolution of cooperation. IIASA Interim Report. IIASA, Laxenburg, Austria: IR-10-025