On the relationship between evolution of virulence and host demography

The effects of density-dependence on the evolution of virulence in super-infection models is the theme of this paper. The qualitative dynamics of three host-pathogen systems are studied numerically in a virulence-superinfection parameter landscape. It is shown numerically that pathogen's competitive exclusion coexistence and host population extinction depend heavily on the population dynamics of the host population. Reported patterns of diversity found using models without demography, are insufficient to account for the coevolutionary dynamics under defined selective pressures. Specifically, virulence and superinfection in the presence of a variable host population give rise to threshold values that divide (as switches) the regions of coexistence and competitive exclusion. Tight coevolution on a variable host population may occur within regions of parameter space that are not connected. We present our numerical results using a simple host-disease system where a homogeneous host population is invaded by two competing pathogen strains (partial analytical results will be published elsewhere). (C) 1998 Academic Press.