“…Mathematical model, that describes this interaction, could help to understand its dynamic processes and to make practical predictions. Such model could be various type of differential equations: ordinary differential equations [11,23,34], delay differential equations [3,24,31,37], reaction-diffusion equations [4,7,32,36], first order partial differential equations with age-structure [6,13,26,30,35] and so on. In this paper, we will consider the following model, which is formulated from the one in [26] by incorporating the fertility rate τ 1 into the model,…”