mutual cooperation, that in turn, allows them screening the exploitation by defectors throughout the borders of the cluster. It must be mentioned that some authors found an inverse relationship between the formation of clusters and the success of cooperation [@hauert].

In this work we intend to show that the survival of cooperators involves much more than the conformation of clusters. If it depended only on that, cooperation success would increase monotonically with the clustering coefficient of the underlying network. By focusing on the analysis of networks which only differ in their clustering coefficient, in the next sections we show not only that this does not happen (i.e. the equilibrium fraction of cooperators is a non monotonic function of $C$) but also that there is a strong dependence on the composition of the initial population. This hints at the existence of several mechanisms responsible for the expansion or extinction of cluster of cooperators. To find these mechanisms, in the last section we focus on what happens for populations in completely ordered and completely disordered networks. A detailed analysis allows us to understand the important of the initial fraction of cooperators for the evolution of the different systems.

The model
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The 