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UBC Theses and Dissertations

Exploitation of predator-prey associates Dowidar, M. Sameer


A continuous-time model, describing the interaction between a "'facultative"' predator and a prey is used to study the consequences of exploitation of either the predator, the prey or both. The model assumes a logistic growth pattern in absence of the interaction. The change in steady-state levels of the associates due to different combinations of fishing intensities are described mathematically and diagrammatically. The effect of density of predation, on the equilibrium populations associated with the yield of either, or both, the predator and the prey are studied. Yield curves were constructed for both the predator and the prey under different fishing intensities of the other associate. The model is given in a discrete-time form, of which the stochastic version is derived to show the effect of intrinsic variability. The stochastic version was simulated on the computor through the use of random normal deviates. Fair agreement between the calculated values of the variances of the steady states, and those empirically found through simulation is listed. This simple structural model reveals that in such an association, fishing the prey population alone gives a lower maximum sustained yield than can be maintained, if the predator is also fished. It is hoped that such a model, which is a preliminary but a necessary step, will lead to a more comprehensive model applicable to natural fish populations.

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