EvoLudoLab: Space promotes cooperation in the Prisoner's Dilemma
Along the bottom of the applet there are several buttons to control the execution and the speed of the simulations - for details see the EvoLudo GUI documentation. Of particular importance are the parameters button and the data views pop-up list along the top. The former opens a panel that allows to set and change various parameters concerning the game as well as the population structure, while the latter displays the simulation data in different ways.
|New cooperator||New defector|
Note: The shades of grey of the payoff scale are augmented by blueish and reddish shades indicating payoffs for mutual cooperation and defection, respectively.
Spatial Prisoner's Dilemma: pure strategies
The spatial Prisoner's Dilemma supports cooperation within a certain parameter range. In that range cooperators can keep up with defectors by forming clusters and thus reducing interactions with (exploitation from) defectors. Even though the parameter range is rather limited, it still demonstrates that cooperation may persist simply because of spatial dimensions and without the need for sophisticated strategic behavior. Whereas in absence of spatial structures and limited local interactions cooperators would invariably go extinct. The parameters are set to <math>T = 1.07</math> and <math>S = -0.07</math> with individuals arranged on a square <math>70\times 70</math> lattice with four neighbors and players imitating better strategies with a probability proportional to the payoff difference. The inital fraction of cooperators is 50%.
|Snapshot of the spatial arrangement of strategies.|
|Time evolution of the strategy frequencies.|
|Snapshot of the spatial distribution of payoffs.|
|Time evolution of average population payoff bounded by the minimum and maximum individual payoff.|
|Snapshot of payoff distribution in population.|
|Degree distribution in structured populations.|
|Message log from engine.|
The list below describes only the few parameters related to the Prisoner's Dilemma, Snowdrift and Hawk-Dove games. Follow the link for a complete list and detailed descriptions of the user interface and further parameters such as spatial arrangements or update rules on the player and population level.
- reward for mutual cooperation.
- temptation to defect, i.e. payoff the defector gets when matched with a cooperator. Without loss of generality two out of the four traditional payoff values \(R, S, T\) and \(P\) can be fixed and set conveniently to \(R = 1\) and \(P = 0\). This means mutual cooperation pays \(1\) and mutual defection zero. For example for the prisoner's dilemma \(T > R > P > S\) must hold, i.e. \(T > 1\) and \(S < 0\).
- sucker's payoff which denotes the payoff the cooperator gets when matched with a defector.
- punishment for mutual defection.
- Init Coop, init defect
- initial fractions of cooperators and defectors. If they do not add up to 100%, the values will be scaled accordingly. Setting the fraction of cooperators to 100% and of defectors to zero, then the lattice is initialized with a symmetrical configuration suitable for observing evolutionary kaleidoscopes.