ON THE ROLE OF ALLEE EFFECT AND MASS MIGRATION IN SURVIVAL AND EXTINCTION OF A SPECIES

We use interacting particle systems to investigate survival and extinction of a species with colonies located on each site of Z(d). In each of the four models studied, an individual in a local population can reproduce, die or migrate to neighboring sites. We prove that an increase of the death rate when the local population density is small (the Allee effect) may be critical for survival, and that the migration of large flocks of individuals is a possible solution to avoid extinction when the Allee effect is strong. We use attractiveness and comparison with oriented percolation, either to prove the extinction of the species, or to construct nontrivial invariant measures for each model.