My final dissertation chapter explores the paradox of parasites on predators. Parasites likely decrease predator efficiency, which in turn decreases the level of vigilance in the prey, which in turn increases predator efficiency. Parasites are both good and bad for predators--is there an optimal level of parasites?
I modeled the dynamics, isoclines, and equilibria of the system with a Rosenzweig and MacArthur predator-prey model (1963), using a Type I functional response. I used two implementations of prey vigilance: behaviorally fixed, where vigilance remained constant, and behaviorally flexible, where prey could adapt their vigilance to changing predator dynamics.
Predators in the flexible vigilance model saw no real consequence for changes in the prey’s value of vigilance. The behavioral consequences of parasites appear to manifest through lower encounter rates with prey, which reduce the wariness of the prey, which in turn increases predator efficiency. If parasites also reduce predator lethality, prey will respond to this weakness with reduced vigilance, increasing predator efficiency beyond the deficit from reduced lethality.
The model and figures were written in R.
Project link: Github