A predator–prey system may be modeled using the differential equations

˙ x = x(1 − y − ǫx), ˙ y = y(−1 + x − ǫy), where x(t) is the population of prey and y(t) is the predator population size at time t , respectively. Classify the critical points for ǫ ≥ 0 and plot phase portraits for the different types of qualitative behavior. Interpret the results in physical terms.