Understanding and predicting responses to increased mortality is important for conservation biology and population management strategies. In stage-structured populations, increased mortality of a particular stage can have the counterintuitive effect of causing increased abundance in one or more stages (called stage-specific overcompensation in density) or the whole population (called a hydra effect). We analyzed an n-stage, single-species, ordinary differential equation model in order to explore the mechanisms driving overcompensation in density and hydra effects in stage-structured populations. We find that in the absence of inter-stage competition, overcompensation in density only occurs if intra-stage competition in one stage is sufficiently strong to cause overcompensation in the maturation or reproductive rate of that stage (i.e., increased input causes decreased output for that stage). When there is inter-stage competition, overcompensation in density can also be driven by sufficiently strong inter-stage competition, even in the absence of overcompensation in any ecological rate. Hydra effects arise under the same conditions and are more likely to be caused by sufficiently strong intra-stage competition. We interpret our results in terms of the direct and indirect effects between stages, which helps clarify the relationships between stage-specific overcompensation in density, overcompensation in ecological rates and hydra effects.

了解和预测增加死亡率的反应对于保护生物学和种群管理策略很重要。在阶段结构化的种群中，特定阶段死亡率的增加可能会引起反常的影响，从而导致一个或多个阶段的丰度增加（称为阶段特定的密度过度补偿）或整个种群的增加（称为水hydr效应）。我们分析的ñ阶段单物种常微分方程模型，以探讨驱动阶段结构种群密度和水合效应过度补偿的机制。我们发现，在没有阶段间竞争的情况下，仅当一个阶段的阶段内竞争足够强大而导致该阶段的成熟度或繁殖率发生过度补偿时（即输入增加导致该阶段的产出减少），密度才会发生过度补偿。阶段）。当存在阶段间竞争时，即使没有任何生态速率的过度补偿，也可以通过足够强的阶段间竞争来驱动密度的过度补偿。九头蛇效应是在相同条件下产生的，更可能是由足够强的阶段内竞争引起的。