Parasites and host population dynamics

Abstract

Abstract The role that parasites have in influencing the dynamics of their host population has been a central question in the study of wildlife diseases (Kennedy 1975; Grenfell and Dobson 1995). Ecologists and wildlife managers have typically assumed that the answer to this question is ‘No’, believing that para-sites are normally benign, specialized predators that live in a delicate balance with their hosts (Lack 1954). Whilst epidemic outbreaks of disease may cause massive host mortalities, they were explained as cases where environmental factors had disturbed the careful balance and thus rationalized as unusual exceptions to the general rule of no impact. It was even frequently argued that parasites were unlikely to impact on host population dynamics because if their actions led to the death of the host, then the parasite would also die. Theoretical and empirical evidence is now available that highlights the fallacy of this view. Since the lifetime reproductive success of parasites does not depend upon survival alone, but on the interactions between survival, reproduction, and transmission which determine the parasites ability to establish breeding offspring in new hosts, parasites can indeed have highly detrimental effects on their hosts (Box 3.1).