Fig. 1
From: High cost enhances cooperation through the interplay between evolution and self-organisation
The model. a The world is a square lattice with connectivity k=8 (every node has 8 neighbours) and wrapped boundary conditions. Individuals produce public good at rate p, shared in equal parts (p/9) among all neighbouring nodes and self. b Individuals compete for reproduction into an adjacent empty spot. Probability of reproduction depends on fitness f i , which is the difference between benefits and costs. The sum of the public good an individual collects from itself and the neighbours, if any, is p sum=(p a +p b +…+p i )/9, and confers a benefit b·p sum. Individuals pay a fitness cost proportional to the public good they produce: c·p. Successful reproduction yields a copy of the selected individual. Mutations occur with probability μ and change the public good production rate by a small random number chosen uniformly in the interval [−δ/2,δ/2]. Individuals have a small probability k move to move to a random adjacent node, and can die with probability k death, leaving the node empty (See Methods for the details of the models)