“…However, the idea in [9], [10], [29] to acquire the asymptotic behavior of system (1.2) is unavailable for system (1.4) because the Fokker−Planck equation corresponding to system (1.4) is of degenerate type. In this paper, one of our aims is to study the stationary distribution of system (1.4) by applying Markov semigroup theory ( [13], [14], [16], [17], [23], [24]) which is different from the idea in [8] and [30]. However, perturbations that biological populations suffer often appear periodic phenomena, such as seasonal effect, individual lifecycle and so on.…”