The effect of reservoir-based chemical defense on predator-prey dynamics

Numerous animal species use defense mechanisms such as chemical secretion to defend against attacks of predators. Although defense mechanisms have the potential to considerably change the dynamics and stability of a system, few theoretical studies exist. In this paper, we focus on predator-prey systems with reservoir-based chemical defense, which is also called "reducible defense" and is widespread among invertebrates. The predator has to attack often enough to disarm and consume prey, and prey can biosynthetically restore lost secretion. The model includes these features in the functional response, and in a separate equation for the stored amount of secretion. Additionally, our model takes into account that defense involves metabolic costs, reducing population growth of the prey. By performing computer simulations, we show that the defense mechanism causes the predator to take more time to consume prey. This time is increased more efficiently when the prey invests in a large reservoir rather than in fast restoration of secretion. We also investigate the stationary states resulting on longer time scales, finding that both predator and prey can become considerably more abundant due to the defense mechanism. However, investment into defenses pays off only when predator density is large enough and costs of defense are not too high.