WHAT ARE THE EMERGING PRINCIPLES OF PARASITE ECOLOGY THAT RELATE TO CONSERVATION BIOLOGY?
Authors: The group
This short paper will review the emerging principles of epidemiology and how they can be used to illuminate problems within conservation biology.
A. We start by making some broad comments about parasites and raise hypotheses that reveal the important role of parasites:
- Parasitism is a pervasive component of all ecosystems
- There are probably more parasites than free-living organisms
- Parasites are a major force maintaining diversity
- Parasitism was a main driving force leading to the evolution of sex
B. We summarise the 10 main principles of epidemiology and why they are important
- Parasite establishment requires R0>1
- There is a critical host population size for parasite persistence and extinction although the critical density for invasion may differ from that for extinction
- The dynamics and evolution of a parasite are determined by whether transmission rates are density or frequency dependent
- Observed levels of prevalence reflect the interaction between host susceptibility and exposure to parasites but does not necessarily indicate the significance of parasitism to host regulation
- Generalist pathogens pose more of a threat to rare species than specialist pathogens, particularly when vector transmitted
- The relatively high reproductive rates of pathogens creates the potential for rapid evolution in epidemiological parameters
- Herd immunity is a function of the force of infection
- Pathogen fitness is a trade off between virulence and transmission
- Changing host abundance has a strong effect on host parasite dynamics with significant second order effects on community structure
- Parasitic helminths are invariably aggregated within their host population and this tends to stabilise host parasite dynamics but reduce the efficacy of control programmes.
C. We consider what a vet or conservation biologist needs to examine:
- Age prevalence curves to estimate R0
- Vaccination aims to reduce the size of the susceptible host population to R0<1