  A microscopic approach to macroeconomic features is intended. A model for
macroeconomic behavior under heterogeneous spatial economic conditions is
reviewed. A birth-death lattice gas model taking into account the influence of
an economic environment on the fitness and concentration evolution of economic
entities is numerically and analytically examined. The reaction-diffusion model
can be also mapped onto a high order logistic map. The role of the selection
pressure along various dynamics with entity diffusion on a square symmetry
lattice has been studied by Monte-Carlo simulation. The model leads to a sort
of phase transition for the fitness gap as a function of the selection pressure
and to cycles. The control parameter is a (scalar) ''business plan''. The
business plan(s) allows for spin-offs or merging and enterprise survival
evolution law(s), whence bifurcations, cycles and chaotic behavior.
