Vincent, Thomas L., and Joel S. Brown. “Evolution under nonequilibrium dynamics.” Mathematical Modelling 8 (1987): 766-771.
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We define an ESS to be a set of strategies (a coalition) which can persist together through time and which are resistant to invasion by rare alternative strategies. In spite of large fluctuations in population density and relatively small fluctuations in strategy frequencies, we show that the evolutionary game will still produce a well-defined coalition of strategies as an ESS. Since population fluctuations are endemic properties of ecosystems, it is significant that although such fluctuations may alter the strategies of the coalition, they do not preclude the existence of an ESS.