where u 1 and u 2 stand for the densities of prey and predator population, respectively, ρ 1 , ρ 2 stand for the catchability parameter, the effort applied to harvest the prey species, respectively, ρ 3 and ρ 4 denote appropriate real constants, γ i (i = 1, 2, 3, 4), κ have the same implication as those in model (1.1). Based on the biological viewpoint, we