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
Stage dependent predation may give rise to the hydra effect--the increase of predator density at equilibrium as its mortality rate is raised. Management strategies that adjust predator harvest rates or quotas based on responses of populations to past changes in capture rates may eventually lead to a catastrophic collapse of predator species. A proposed threshold management policy avoids the hydra effect and its subsequent danger of predator extinction. Suggestions to extend the application of threshold policies in areas such as intermediate disturbance hypothesis, density-trait mediated interactions and non-optimal anti-predatory behavior are put forward.
Assuntos
Ecossistema , Modelos Biológicos , Comportamento Predatório , Animais , Conservação dos Recursos Naturais , PesqueirosRESUMO
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.