Effect of population size in a Prey-Predator model

We consider a stochastic version of the basic predator-prey differential equation model. The model, which contains a parameter ω which represents the number of individuals for one unit of prey If x denotes the quantity of prey in the differential equation model x = 1 means that there are ω individuals in the discontinuous one is derived from the classical birth and death process. It is shown by the mean of simulations and explained by a mathematical analysis based on results in singular perturbation theory (the so called theory of Canards) that qualitative properties of the model like persistence or extinction are dramatically sensitive to ω. For instance, in our example, if ω = 10 we have extinction and if ω = 10 we have persistence. This means that we must be very cautious when we use continuous variables in place of jump processes in dynamic population modeling even when we use stochastic differential equations in place of deterministic ones.