  We discuss several models of the dynamics of interacting populations. The
models are constructed by nonlinear differential equations and have two sets of
parameters: growth rates and coefficients of interaction between populations.
We assume that the parameters depend on the densities of the populations. In
addition the parameters can be influenced by different factors of the
environment. This influence is modelled by noise terms in the equations for the
growth rates and interaction coefficients. Thus the model differential
equations become stochastic. In some particular cases these equations can be
reduced to a Foker-Plancnk equation for the probability density function of the
densities of the interacting populations.
