BIFURCATION ANALYSIS OF A GENERALIZED GAUSE MODEL WITH PREY HARVESTING AND A GENERALIZED HOLLING RESPONSE FUNCTION OF TYPE III∗

Abstract. In this paper we study a generalized Gause model with prey harvesting and a generalized Holling response function of type III: p(x) = mx2 ax2+bx+1. The goal of our study is to give the bifurcation diagram of the model. For this we need to study saddle-node bifurcations, Hopf bifurcation of codimension 1 and 2, heteroclinic bifurcation, and nilpotent saddle bifur-cation of codimension 2 and 3. The nilpotent saddle of codimension 3 is the organizing center for the bifurcation diagram. The Hopf bifurcation is studied by means of a generalized Liénard system, and for b = 0 we discuss the poten-tial integrability of the system. The nilpotent point of multiplicity 3 occurs with an invariant line and can have a codimension up to 4. But because it occurs with an invariant line, the effective highest codimension is 3. We de-velop normal forms (in which the invariant line is preserved) for studying of the nilpotent saddle bifurcation. For b = 0, the reversibility of the nilpotent saddle is discussed. We study the type of the heteroclinic loop and its cyclicity. The phase portraits of the bifurcations diagram (partially conjectured via the results obtained) allow us to give a biological interpretation of the behavior of the two species