Chapman-Enskog asymptotic procedure in structured population dynamics

Complexity of many biological models often makes impossible their robust theoretical and numerical analysis and thus requires a systematical method of reducing the number of variables in the system in such a way that the dynamics of the simplified model approximates the original way in a reasonable way. Such an aggregation of variables is often done by ad hoc methods. In turns out that in many biological systems the well-known Chapman-Enskog asymptotic procedure is well suited for aggregation which then can be viewed as passing from a microscopic (kinetic) to a macroscopic (hydrodynamic) description of the system. We demonstrate this approach by applying it to an age- and space-structured population model.