“…In particular, special attention has been paid to the problem of modelling migratory movements. Within the class of discrete time models, it is worthwhile to mention the branching process with immigration, the branching process with time-dependent immigration, the branching process with immigration only after empty generation, branching processes with migration or the branching process with immigration in varying or random environment (for their description, see the pioneer works [11,12], [4], [22], [21] and [18], respectively, or [6] for a review of them) and the age-dependent branching process with immigration or its generalization, the Sevast'yanov branching process with immigration (see [15] and [28], respectively, for their description), in continuous time among others.…”