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Bifurcations of invariant tori in predator-prey models with seasonal prey harvesting. (English) Zbl 1294.34050
Subject of the paper is a predator-prey model whose non-monotonous functional response decays exponentially, and where prey harvesting takes place. First, the harvesting is assumed to have constant yield $$h$$, and six possible equilibria in the closed positive quadrant are determined, three of them on the boundary. Depending on $$h$$ and three additional parameters, the existence, types, and degeneracies of these equilibria are next investigated. From these results, and using a known statement on the generalized Liénard system, the authors then derive the different possibilities of bifurcation: saddle-node and (degenerate) Hopf bifurcation with the existence of up to two limit cycles. Moreover, a Bogdanov-Takens bifurcation is proved at one of the inner equilibria. In the last part of the paper, the authors add to the constant-yield harvesting h a time-periodic harvesting with small amplitude $$A$$, and then prove the existence of an asymptotically stable periodic solution. Finally, under some non-resonant conditions, an asymptotically stable invariant torus is shown to bifurcate from a stable limit cycle that exists for $$A=0$$. Numerical simulations illustrate the preceding results and also indicate the bifurcation of a stable invariant homoclinic torus from the homoclinic loop that exists when $$A=0$$.

##### MSC:
 34C60 Qualitative investigation and simulation of ordinary differential equation models 34C23 Bifurcation theory for ordinary differential equations 92D25 Population dynamics (general) 37G15 Bifurcations of limit cycles and periodic orbits in dynamical systems 37G20 Hyperbolic singular points with homoclinic trajectories in dynamical systems 34C05 Topological structure of integral curves, singular points, limit cycles of ordinary differential equations 34D20 Stability of solutions to ordinary differential equations
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