  We investigate the time evolution and stationary states of a stochastic,
spatially discrete, population model (contact process) with spatial
heterogeneity and imposed drift (wind) in one- and two-dimensions. We consider
in particular a situation in which space is divided into two regions: an oasis
and a desert (low and high death rates). Carrying out computer simulations we
find that the population in the (quasi) stationary state will be zero,
localized, or delocalized, depending on the values of the drift and other
parameters. The phase diagram is similar to that obtained by Nelson and
coworkers from a deterministic, spatially continuous model of a bacterial
population undergoing convection in a heterogeneous medium.

Statistical Mechanics;Populations and Evolution