“…Most of the works in the earlier literature were devoted to studying the linear diffusion case: that is, m = n = 1, p = q = 2 (see, for example, [1,7,13,16,20,21]). We also mention that, as a special case, the coexistence steady state for biological community system has also been investigated in some references: see [3,5,6,8,18]. The biological background makes it very interesting to study the coexistence periodic solutions of a nonlinear diffusion system of the same type as (1.1).…”