Figure 1.

(a–c) Birth–death updating with environmental heterogeneity in reproductive fitness. At location i, an A-individual (mutant) has fitness a_i and a B-individual (resident) has fitness b_i. At each time step, an individual is selected to reproduce with probability proportional to fitness; the offspring then replaces a random individual chosen for death. Here, the individual at location 8 reproduces and its offspring replaces the individual at location 2. Although the parent has fitness b₈, the offspring has fitness b₂ since it is in a different environment. While dispersal is determined by a complete graph (light grey), the population cannot be considered ‘unstructured’ since one must keep track of locations due to environmental variations in fitness (which could result from variations in resources).