0 0.2 0.4 0.6 0.8 1 r$_{31}$ 0.005 0.01 0.015 0.02 0.025 0.03 P[N>0] Model B FIG. 3: Simulation results for r$_{13}$ = 0 . 5. Black circles correspond to r$_{12}$ = 0 . 5, red squares to r$_{12}$ = 0 . 525, and green diamonds to r$_{12}$ = 0 . 55. Other parameter values: µ = 0 . 001, ϵ = 10 − $^{5}$, and α = 1. FIG. 4: Simulation results for r$_{13}$ = 0 . 5 and r$_{12}$ = 0 . 5, and green diamonds to r$_{12}$ = 0 . 5. Black circles correspond to r$_{31}$ = 0 . 05 and red squares r$_{31}$ = 0 . 1. Other parameter values: µ = 0 . 001, and α = 1. considered. First we let a population whose dynamics is given by Model A, evolve for some time in an environment free of the hostile agent. In this environment, both type (1) and type (2) individuals can thrive. The dynamics in an environment free of any hostile agent is described in terms of the generating functions shown in Table I. The introduction of the hostile agent is describe by changing the dynamics of the population to the one described by model B (see the diagram 1 and Table II), which is essentially the same as model A (Table I) but with type (2) individuals doomed to perish. We further assume that the hostile agent is active only for a given period of time, after which its detrimental effect on type (2) organisms ceases and the dynamics of the population reverts to Model A (as per Table I). Parameter values are chosen so the dynamics of the agent-free population is super-critical (i.e. the corresponding survival probability is bigger than zero). After the hostile agent has been 7