Figure 1.

A schematic illustrating temporal (a) and spatial (b) randomness. Cells (assumed to reside on a ring) are represented by circles. Mutants are coloured by reddish tones (marked by m) and wild-types by bluish tones (marked by w). Four consecutive time-steps are shown, and for simplicity it is assumed that the locations of the four mutant cells do not change (which is not the case in general). Saturation of the colour represents cells’ rate values, and the division rates and the death rates can each take two possible values. In (a), at each time step, all mutants and all wild-type cells have the same rate values, but they randomly change from step to step. In (b), both mutants and the wild-type cells have random fitness values determined by the cells’ locations, but they remain constant in time. (Online version in colour.)