Link to this article: http://journals.cambridge.org/abstract_S0956792513000028How to cite this article: M. AL-JARARHA and CHUNHUA OU (2013). Population dynamics with age-dependent diffusion and death rates.In this paper we investigate the population dynamics of a species with age structure in the case where the diffusion and death rates of the matured population are both age-dependent. We develop a new application of the age-structure technique in terms of an integral equation. For unbounded spatial domains, we study the existence of travelling waves, whilst in bounded domains, we investigate the existence of positive steady-state solutions and their stability.Population dynamics with age-dependent diffusion and death rates 473 where u m and u are the population density of the mature and the immature populations, f(u m ) and g(u m ) are the birth and death functions, D I (a) and μ I (a) are the diffusion and death rates of the immature population, and D m and d m are age independent diffusion and death rates of the mature population. They investigated the existence of travelling wave solutions of this model, when the spatial domain is the whole real line R. When the spatial domain is bounded, the above model was studied by Xu and Zhao in [28] and by Jin and Zhao in [11] where they investigated the existence of steady-state solutions. Also, with a slight modification, these types of models have been recently studied by many mathematicians. For example, Al-Omari and Gourley [1], Gourley and Kuang in [4], Gourley and So in [5], Gourley, So, and Wu in [6] and Ou and Wu in [18]. Overall, all these papers study the models with a crucial assumption that the diffusion and death rates of the mature population are constants so that equation (1.4) can be easily derived. Actually, all models above seem to fail if D m (a) and d m (a) are not constants, because equation (1.4) is not valid anymore if both D m (a) and d m (a) are age-dependent.Biologically, it is more realistic to include the age effects in the mathematical models during the whole life of the species. For example, women in the age between 15-40 years have higher birth rate and lower death rate. Another example is the predation of animals; the predation could be heavier on some certain age groups of mature population, which makes the death rate depend on the age. In epidemiology, it is also important to consider the death rate of mature population to be age-dependent. Indeed, the disease may have different infection rates for different age groups of mature population. An example of this is the sexually-transited diseases (STDs), which spread through mature individuals; most AIDS cases occur in young adults. This causes a variation in the death rate amongst the different age of the mature individuals. Therefore, it is natural and more realistic to consider the diffusion and death rates to be age-dependent during all the life time.In this paper, we aim to investigate the populations dynamics for this case (agedependent in the whole life). Therefore, we consider the...