Basson M, Beddington J R, May R M
Renewable Resources Assessment Group, Imperial College of Science, Technology and Medicine, London, England.
Math Biosci. 1991 Apr;104(1):73-95. doi: 10.1016/0025-5564(91)90031-d.
A general, logistic population model is used to explore the dynamics of harvested elephant populations. The model includes two features peculiar to elephant populations and the harvesting of ivory. First, because of the shape of the growth curve of tusks with age, the conversion factor that relates the number of elephants killed to the ivory yield in weight is not constant, but a function of the population size. Second, tusks from animals that die from natural causes can be retrieved and included in the total yield of ivory. The implications of the relationship between tusk size and age of an animal on the maximum sustainable yield in terms of ivory tonnage and in terms of the number of tusks are explored. The nonequilibrium implications of the tusk growth curve on the population dynamics under different harvesting strategies are also investigated. Results indicate that the maximum sustainable yield is achieved at very low harvest rates with population levels close to the pristine equilibrium. When tusks from animals that die of natural causes are included in the harvest, the maximum yield may, depending on the mortality and recruitment parameters, occur when there is no direct harvest.
一个通用的逻辑斯谛种群模型被用于探究被猎杀的大象种群的动态变化。该模型包含大象种群和象牙猎杀的两个独特特征。其一，由于象牙重量随年龄的增长曲线形状，将被杀死大象的数量与象牙重量产量联系起来的转换因子并非恒定不变，而是种群规模的一个函数。其二，死于自然原因的动物的象牙可以被获取并纳入象牙总产量中。本文探讨了动物象牙大小与年龄之间的关系对象牙吨位和象牙数量方面的最大可持续产量的影响。还研究了在不同猎杀策略下，象牙生长曲线对种群动态的非平衡影响。结果表明，在极低的猎杀率且种群水平接近原始平衡状态时可实现最大可持续产量。当将死于自然原因的动物的象牙纳入猎杀范围时，根据死亡率和补充参数的不同，最大产量可能在没有直接猎杀的情况下出现。
