  Much research has focused on the deleterious effects of free-riding in public
goods games, and a variety of mechanisms that suppresses cheating behaviour.
Here we argue that under certain conditions cheating behaviour can be
beneficial to the population. In a public goods game, cheaters do not pay for
the cost of the public goods, yet they receive the benefit. Although this
free-riding harms the entire population in the long run, the success of
cheaters may aid the population when there is a common enemy that antagonizes
both cooperators and cheaters. Here we study models in which an immune system
antagonizes a cooperating pathogen. We investigate three population dynamics
models, and determine under what conditions the presence of cheaters help
defeat the immune system. The mechanism of action is that a polymorphism of
cheaters and altruists optimizes the average growth rate. Our results give
support for a possible synergy between cooperators and cheaters in ecological
public goods games.
