Optimal harvesting, economic discounting and extinction risk in fluctuating populations

R Lande, S Engen, BE Saether - Nature, 1994 - nature.com
Nature, 1994nature.com
DETERMINISTIC models demonstrate that when the economic dis-count rate of future
harvests exceeds a critical value related to population growth rate, the strategy that
maximizes the present value of cumulative harvest is immediate extinction (liquidation) of
the population1–3. Here we analyse stochastic models to derive optimal strategies that
maximize the expected present value of cumulative harvest before extinction of a fluctuating
population. Stochastic models reveal that discount rates below the critical value can …
Abstract
DETERMINISTIC models demonstrate that when the economic dis-count rate of future harvests exceeds a critical value related to population growth rate, the strategy that maximizes the present value of cumulative harvest is immediate extinction (liquidation) of the population1–3. Here we analyse stochastic models to derive optimal strategies that maximize the expected present value of cumulative harvest before extinction of a fluctuating population. Stochastic models reveal that discount rates below the critical value can substantially reduce the mean time to extinction and the expected real harvest before extinction. With an unstable equilib-rium at small population size (Allee effect4–6 or depensation2), the critical discount rate is lower in the stochastic model than in the corresponding deterministic model. These results argue against economic discounting in the development of optimal strategies for sustainable use of biological resources.
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