Figure 1

(Colour online) Strong Allee effect: prey-nullclines are identified by solid blue curves and, accordingly, predator-nullclines are recognized by solid red curves. (a) For \(\beta =10\),the two nullclines cross thrice, then there exist three positive intersections. (b) For \(l= 0.01, \beta =7.8, a = 10.5, b = 5.2, d = 0.3\), in this case we have three interior equilibrium points. (c) Two equilibrium points exists for \(l= 0.2; \beta =9; a = 7.5; b = 4.1; d = 0.7\). (d) For \(l= 0.2, \beta =5, a = 10.5, b = 5.2, d = 0.3\), in this case we obtain the existence of two equilibrium points. (e) one equilibrium point exists for \( l= 0.2; \beta =10.1267155062337; a = 7.5; b = 4.1; d = 0.7\), (f) one equilibrium point for \(l= 0.01, \beta =1, a = 0.5, b = 0.9, d = 0.3\). (g) One equilibrium point for \(l= .1, \beta =5, a = 10.5, b = 5.2, d = 0.3\). (h) For \(l= 0.2; \beta =10.7; a = 7.5; b = 4.1; d = 0.7\), there exists no interior equilibrium point.