RICH DYNAMICS OF A SIMPLE SI MODEL WITH TWO AGE GROUPS

Resumo

The objective of this paper is to study the global dynamics of a simple SI model with two explicit age groups. We divide the population into juvenile and adult groups. Only adults are assumed to be sexually active and we implicitly assume that the sex ratio is constant.

We also assume that infected adults may produce both susceptible newborns and infected newborns. We show that such models can produce the often observed and feared scenario of susceptible extinction. This suggests that age structure alone will not remove the total extinction dynamics in a typical ratio-dependent predator-prey model.

An important feature of our work is that our analytical results are all presented in terms of the biologically meaningful threshold values.