RESUMO
Continuous time models of single exploited populations usually generate outcomes expressing a dependence of yield and economic items on harvest intensity. In this work it is shown that a known threshold policy is able to generate yield and related economic items that do not depend on harvest intensity, but rather on the values of the population threshold itself and the species intrinsic parameters. It is argued that since this result can be carried over to other models of single species dynamics, it may have significant implications in the management and conservation of exploited populations.
Assuntos
Conservação dos Recursos Naturais , Extinção Biológica , Modelos Biológicos , Animais , Pesqueiros/economia , Pesqueiros/estatística & dados numéricos , Dinâmica PopulacionalRESUMO
In a plant-herbivore system, a management strategy called threshold policy is proposed to control grazing intensity where the vegetation dynamics is described by a plant-water interaction model. It is shown that this policy can lead the vegetation density to a previously chosen level under an overgrazing regime. This result is obtained despite both the potential occurrence of vegetation collapse due to overgrazing and the possibility of complex dynamics sensitive to vegetation initial densities and parameter uncertainties.
Assuntos
Animais Domésticos/metabolismo , Cadeia Alimentar , Modelos Biológicos , Plantas/metabolismo , Água/metabolismo , Algoritmos , Criação de Animais Domésticos , Animais , Animais Domésticos/crescimento & desenvolvimento , Conservação dos Recursos Naturais , Ecossistema , Desenvolvimento Vegetal , Dinâmica PopulacionalRESUMO
Yodzis discusses how the differing biological assumptions as to predator interference on the forms of predator-prey models can influence the conclusion to be drawn from multispecies population models with respect to the way predators affect human harvesting of natural populations. To deal with these intricacies related to biological assumptions and fishery management policies, a specific management strategy called threshold policy is proposed. It is shown that its application to the same models analysed by Yodzis leaves the behaviour of the managed population less sensitive to the underlying biological features and assumptions as well as parameter uncertainties. The same management strategy is proposed for the same models in the context of the timely issue of predator culling in fisheries. Interestingly, the fishery yield for each model is exactly the same despite their different biological assumptions.
Assuntos
Pesqueiros , Peixes/crescimento & desenvolvimento , Modelos Biológicos , Comportamento Predatório , Animais , Conservação dos Recursos Naturais/métodos , Dinâmica Populacional , Recursos HumanosRESUMO
The stability of predator-prey models, in the context of exploitation of renewable resources, subject to threshold policies (TP) is studied in this paper using the idea of backstepping and control Liapunov functions (CLF) well known in control theory, as well as the concept of virtual equilibria. TPs are defined and analysed for different types of one and two species predator-prey models. The models studied are the single species Noy-Meir herbivore-vegetation model, in a grazing management context, as well as the Rosenzweig-MacArthur two species predator-prey model, in a fishery management context. TPs are shown to be versatile and useful in managing renewable resources, being simple to design and implement, and also yielding advantages in situations of overexploitation.