264870.fig.002a
(a)
264870.fig.002b
(b)
264870.fig.002c
(c)
264870.fig.002d
(d)
Figure 2: The time histories and phase portrait of system (4.1) with the following parameters: , and . Hopf bifurcation occurs from the positive equilibrium . The initial value is (0.2, 2).