Duplicate title to Brännström, Å., Gross, T., Blasius, B., & Dieckmann, U. ORCID: https://orcid.org/0000-0001-7089-0393 (2011). Consequences of fluctuating group size for the evolution of cooperation. Journal of Mathematical Biology 63 (2) 263-281. 10.1007/s00285-010-0367-3.