EvoLudoLab: Spatial 2x2 Game - Bistability

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.

Color code:	Cooperators	Defectors
	New cooperator	New defector

Payoff code:	Low									High

Note: The shades of grey of the payoff scale are augmented by blueish and reddish shades indicating payoffs for mutual cooperation and defection, respectively.

Bistability

In well-mixed populations either type \(A\) or type \(B\) players thrive and take over the entire population. In spatial populations the same holds but the odds are hugely in favor of \(A\) types because they no longer need to exceed the threshold frequency on a global scale but rather only locally. Therefore, a sufficiently big initial cluster of \(A\)'s exists, ensures their survival and seeds their victory, or, they quickly disappear within the first few generations.

The bi-stability of this system is nicely illustrated when running the above setting several times. Sometimes the system converges to all cooperators and sometimes all defectors. The parameters are set to \(R = 1, P = 0, T = 0.9\) and \(S = -0.54\) with Moore neighborhood and players imitating better strategies proportional to the payoff difference and an initial fraction of 50% \(A\)'s.

	Data views
Strategies - Structure	Snapshot of the spatial arrangement of strategies.
Strategies - Mean	Time evolution of the strategy frequencies.
Fitness - Structure	Snapshot of the spatial distribution of payoffs.
Fitness - Mean	Time evolution of average population payoff bounded by the minimum and maximum individual payoff.
Fitness - Histogram	Snapshot of payoff distribution in population.
Structure - Degree	Degree distribution in structured populations.
Console log	Message log from engine.

Game parameters

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

reward for mutual cooperation.

Temptation

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

sucker's payoff which denotes the payoff the cooperator gets when matched with a defector.

Punishment

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.