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- Bifurcation structures in a 2D exponential diffeomorphism with Allee effectPublication . Rocha, J. Leonel; Taha, Abdel-KaddousAn embedding of one-dimensional generic growth functions into a two-dimensional diffeomorphism is considered. This family of unimodal maps naturally incorporates a key item of ecological and biological research: the Allee effect. Consequently, the presence of this species extinction phenomenon leads us to a new definition of bifurcation for this two-dimensional exponential diffeomorphism: Allee’s effect bifurcation. The stability and the nature of the fixed points of the two-dimensional diffeomorphism are analyzed, by studying the corresponding contour lines. Fold and flip bifurcation structures of this exponential diffeomorphism are investigated, in which there are flip codimension-2 bifurcation points and cusp points, when some parameters evolve. Numerical studies are included.
- Homoclinic and big bang bifurcations of an embedding of 1D Allee's functions into a 2D diffeomorphismPublication . Rocha, J. Leonel; Taha, Abdel-Kaddous; Fournier-Prunaret, D.In this work a thorough study is presented of the bifurcation structure of an embedding of one-dimensional Allee's functions into a two-dimensional diffeomorphism. A complete classification of the nature and stability of the fixed points, on the contour lines of the two-dimensional diffeomorphism, is provided. A necessary and sufficient condition so that the Allee fixed point is a snapback repeller is established. Sufficient conditions for the occurrence of homoclinic tangencies of a saddle fixed point of the two-dimensional diffeomorphism are also established, associated to the snapback repeller bifurcation of the endomorphism defined by the Allee functions. The main results concern homoclinic and big bang bifurcations of the diffeomorphism as "germinal" bifurcations of the Allee functions. Our results confirm previous predictions of structures of homoclinic and big bang bifurcation curves in dimension one and extend these studies to "local" concepts of Allee effect and big bang bifurcations to this two-dimensional exponential diffeomorphism.