Figure 6

The trivial equilibrium \(\bar{E}_{3,0}\) is represented by the circle “”, the unstable endemic equilibrium \(\bar{E}_{3,1}\) is denoted by the rhombus “”, and the stable endemic equilibrium \(\bar{E}_{3,2}\) is represented by the star “”. Simulations have been done with parameter values \(\lambda = 10\), \(\mu = 0.1\), \(\beta = 0.5\), \(\gamma = 0.1\), and \(h = 30\). Part (a) is produced with \(m = 0.8m^{\star }\), while part (b) is produced with \(m = 1.5m^{\star }\)