Wikström Anders, Ripa Jörgen, Jonzén Niclas
Department of Biology (Theoretical Population Ecology and Evolution Group), Ecology Building, Lund University, SE-223 62 Lund, Sweden.
Theor Popul Biol. 2012 Dec;82(4):348-54. doi: 10.1016/j.tpb.2011.12.008. Epub 2011 Dec 27.
Understanding the processes generating fluctuations of natural populations lies at the very heart of academic ecology. It is also very important for applications such as fisheries management and pest control. We are interested in the effect of harvesting on population fluctuations and for that purpose we develop and analyze an age-structured model where recruitment is a stochastic process and the adult segment of the population is harvested. When a constant annual harvest is taken the coefficient of variation of the adult population increases for most parameter values due to the age truncation effect, i.e. an increased variability in a juvenescent population due to the removal of older individuals. However, if a constant proportion of the adults is harvested the age truncation effect is sometimes counteracted by a stabilizing dynamic effect of harvesting. Depending on parameter values mirroring different life histories, proportional harvest can either increase or decrease the relative fluctuations of an exploited population. When there is a demographic Allee effect the ratio of juveniles to adults may actually decrease with harvesting. We conclude that, depending on life history and harvest strategy, harvesting can either reinforce or dampen population fluctuations due to the relative importance of stabilizing dynamic effects and the age truncation effect. The strength of the latter is highly dependent on the fished population's endogenous, age-structured dynamics. More specifically, we predict that populations with strong and positively autocorrelated dynamics will show stronger age truncation effect, a testable prediction that offers a simple rule-of-thumb assessment of a population's vulnerability to exploitation.
理解自然种群波动产生的过程是理论生态学的核心所在。这对于渔业管理和害虫防治等应用领域也非常重要。我们关注捕捞对种群波动的影响，为此我们构建并分析了一个年龄结构模型，其中补充是一个随机过程，且种群中的成年部分会被捕捞。当进行恒定的年度捕捞时，由于年龄截断效应，即由于老年个体的移除导致幼年种群变异性增加，成年种群的变异系数对于大多数参数值都会增加。然而，如果捕捞成年个体的恒定比例，年龄截断效应有时会被捕捞的稳定动态效应所抵消。根据反映不同生活史的参数值，比例捕捞既可能增加也可能减少被开发种群的相对波动。当存在人口统计学上的阿利效应时，幼体与成体的比例实际上可能会随着捕捞而降低。我们得出结论，取决于生活史和捕捞策略，由于稳定动态效应和年龄截断效应的相对重要性，捕捞既可能增强也可能抑制种群波动。后者的强度高度依赖于被捕捞种群的内源性年龄结构动态。更具体地说，我们预测具有强烈且正自相关动态的种群将表现出更强的年龄截断效应，这是一个可检验的预测，为评估种群对开发的脆弱性提供了一个简单的经验法则。
