An ecoepidemic model with diseased predators and prey group defense

In this paper we consider a prey population that gathers in herds, together with its interactions with predators. The latter are affected by a disease, and only the healthy individuals hunt. The defensive attitude of the prey is reflected in the fact that mostly the individuals at the border of the herd suffer from the attacks of the predators. Equilibria and their stability are fully analysed. The system can either eliminate the predators, or the disease can be eradicated, or finally infected and healthy predators can coexist with prey. In particular circumstances persistent population oscillations can arise. The ultimate behavior of the system is characterized by two suitably introduced parameters, one of demographic nature, the other mainly of epidemiological significance. As in other ecoepidemic models, the analysis points out that the disease plays a relevant influence also when group defense is considered, so that the ultimate outcome of the system is not prescribed just by demographic considerations.