Destabilising effect of periodic harvest on population dynamics

The effect of periodic harvesting or feeding by a constant amount in nonlinear population dynamics was studied. We used for discussion the Ricker model, and a host–parasite model proposed by Beddington et al. (Beddington, J.R., Free, C.A., Lawton, J.H., 1975. Nature 255, 58–60). Even so simple an action may in the long term qualitatively modify the behaviour of the system. From initially periodic dynamics the action might lead to completely chaotic dynamics, and from initially chaotic dynamics, the action might completely stabilise the orbits. In addition, as a general rule, harvesting tends to destabilise the dynamics while feeding tends to stabilise the dynamics.