  Besides the structure of interactions within networks, also the interactions
between networks are of the outmost importance. We therefore study the outcome
of the public goods game on two interdependent networks that are connected by
means of a utility function, which determines how payoffs on both networks
jointly influence the success of players in each individual network. We show
that an unbiased coupling allows the spontaneous emergence of interdependent
network reciprocity, which is capable to maintain healthy levels of public
cooperation even in extremely adverse conditions. The mechanism, however,
requires simultaneous formation of correlated cooperator clusters on both
networks. If this does not emerge or if the coordination process is disturbed,
network reciprocity fails, resulting in the total collapse of cooperation.
Network interdependence can thus be exploited effectively to promote
cooperation past the limits imposed by isolated networks, but only if the
coordination between the interdependent networks is not disturbed.
