Stochasticity, Selection, and the Evolution of Cooperation in a Two-Level Moran Model of the Snowdrift Game

Figure 1

Two-Level Moran Process. This is a condensed representation of the two-level, discrete time Moran process in our model. Each isolated cluster of red and blue ovals is a “group," while the ovals themselves are “individuals,” which come in two varieties, cooperators (blue) and defectors (red). The set of six groups constitutes a metapopulation. Within a group, an individual is chosen to reproduce and replace some individual in the same group: the arrow represents an individual having an identical offspring, which replaces another individual in the group. (The replaced individual has a dashed border around it.) Across groups, a group is chosen to reproduce and replace some group in the metapopulation. The group in the bottom-left corner reproduces and replaces the group in the top-right corner. (The replaced group has a dashed border around it.)