Dynamic Use of Closures and Imperfectly Enforced Quotas in a Metapopulation

The dynamic efficiency of closures in bioeconomic systems depends upon stock levels and in situ values that evolve over time, and on relative costs of implementation. A model of a harvested metapopulation is presented in which second-best reduction of harvest from open-access levels using input quotas balances monitoring costs against dynamic benefits of mitigating overharvesting. Temporary or permanent closures—though generally still second best—are preferable to quotas under certain conditions, as demonstrated for a representative patch and time period. Interactions between patches are discussed. Numerical solutions illustrate comparative dynamics of closure use, and show their potential benefits in a dynamic regulatory path.     

具有异质性扩散率的传染病模型分析

为了刻画大尺度空间范围内的个体移动对疾病传播的影响,主要研究了异质集合种群网络的传染病传播过程。由于城市之间存在规模以及交通发达程度等方面的异质性,扩散率也存在一定的异质性。以城市作为节点,建立了具有异质性扩散率的传染病动力学模型,更加准确地刻画了网络结构以及人们的出行对疾病传播的影响。通过对系统进行定性及稳定性分析,发现系统存在一个无病平衡点,并得到了无病平衡点不稳定的阈值条件。当达到疾病爆发的阈值条件时,系统存在唯一的地方病平衡点,并且地方病平衡点是局部渐近稳定的。通过数值模拟验证了理论的正确性。研究表明,增大扩散率能加快疾病的流行速度,因此,通过有效控制大城市的人口出行率可以在一定程度上控制疾病的爆发。