Cooperation in the two-population snowdrift game with punishment   enforced through different mechanisms
  I study two mechanisms based on punishment to promote cooperation in the two-population snowdrift game. The first mechanism follows the traditional approach in the literature and is based on the inclusion of a third additional strategy in the payoff matrix of the stage-game. The second mechanism consists of letting cooperators to punish defectors with a given exogenous frequency. While both mechanisms share the same result regarding the minimum required level of punishment in order to eliminate defectors in both populations, stability in the mechanism following the second approach is more robust in the sense that extinction of defectors is a globally asymptotically stable state for any interior initial conditions in the phase space. Results were obtained analytically through non-linear differential equations and also using an agent-based simulation. There was a good level of agreement between both approaches with respect to the evolutionary pattern over time and the possible steady-states. 
Andr\'e Barreira da Silva Rocha
q-bio.PE