Destabilising effect of periodic harvest on population dynamics

The effect of periodic harvesting or feeding by a constant amount in nonlin ear population dynamics was studied. We used for discussion the Ricker mode l, 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 ac tion may in the long term qualitatively modify the behaviour of the system. From initially periodic dynamics the action might lead to completely chaot ic dynamics, and from initially chaotic dynamics, the action might complete ly stabilise the orbits. In addition, as a general rule, harvesting tends t o destabilise the dynamics while feeding tends to stabilise the dynamics. ( C) 2000 Elsevier Science B.V. All rights reserved.