Figure 2.

Successful invaders. The big black point is the resident strategy. The cloud shows the distribution of the first successful mutation that replaces the resident. The arrowhead indicates the centre of gravity of the cloud of successful invaders. The number quantifies how many unsuccessful mutants are generated on average before one successful mutant takes over. (a) Typically, an ALLD population is taken over after a while by a mutant with TFT-like behaviour. (b) A TFT population is then quickly taken over and the dynamics move towards some new state close to the edge from TFT to ALLC. (c) If the new resident strategy is carefully forgiving—in this example we have (p, q) = (0.9,0.5)—the population stays at this state for a long time, but will eventually move closer to ALLC. (d) An ALLC population is quickly taken over and the population returns to ALLD. As in figure 1, mutations are generated from a uniform distribution. Parameter values are population size N = 100, benefit b = 10 and cost c = 1.