  We adopt an operatorial method based on the so-called creation, annihilation
and number operators in the description of different systems in which two
populations interact and move in a two-dimensional region. In particular, we
discuss diffusion processes modeled by a quadratic hamiltonian. This general
procedure will be adopted, in particular, in the description of migration
phenomena. With respect to our previous analogous results, we use here
fermionic operators since they automatically implement an upper bound for the
population densities.
