“…For the simplest among this models, the branching random walk, much has been done: for instance in [4,5,7,32,45,47] one finds characterization of the persistence/disappearance of genotypes (seen as locations for the model), on general space structures; the same can be found, for some random graphs, in [8,35]. Stochastic modelling and interacting particle systems have been successfully applied to biology and ecology (see [1,2,3,12,13,24,25,26,28,19,48] just to mention a few). Although stochastic modelling is very interesting and complex, here we will assume that over many generations, our populations have been sufficiently large to justify the use of a model where stochasticity appears only in the random time at which the disturbance strikes.…”