The Lotka-Volterra model takes its name from the authors of the ﬁrst investigations of interacting populations. Volterra (1926a; 1926b; 1931) based his considerations on the unexpected results of the ﬁeld observations of the biologist D’Ancona (1954) on the ﬁshing catches in the Adriatic sea after the First World War. Other models were developed later to avoid the main drawback of the original Lotka-Volterra model, namely, the neutral stability of its interior equilibrium point. This makes the solutions sensitive to variations of the initial conditions of the system, and therefore biologically they are not very satisfactory. These modiﬁcations include at ﬁrst quadratic models, which incorporate a logistic growth term for at least one of the two populations, and then also other nonlinear terms, such as the eﬀect of satiation in feeding.