  This paper is concerned with an age-structured model in population dynamics.
We investigate the uniqueness of solution for this type of nonlinear
reaction-diffusion problem when the source term depends on the density,
indicating the presence of, for example, mortality and reaction processes. Our
result shows that in a spatial environment, if two population densities obey
the same evolution equation and possess the same terminal data of time and age,
then their distributions must coincide therein.
