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首页> 美国卫生研究院文献>PLoS Clinical Trials >Superadditive and subadditive dynamics are not inherent to the types of interacting threat
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Superadditive and subadditive dynamics are not inherent to the types of interacting threat

机译：超加性和亚加性动力学不是交互威胁类型所固有的

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摘要

Species and ecosystems usually face more than one threat. The damage caused by these multiple threats can accumulate nonlinearly: either subadditively, when the joint damage of combined threats is less than the damages of both threats individually added together, or superadditively, when the joint damage is greater than the two individual damages added together. These additivity dynamics are commonly attributed to the nature of the threatening processes, but conflicting empirical observations challenge this assumption. Here, we use a theoretical model to demonstrate that the additivity of threats can change with different magnitudes of threat impacts (effect of a threat on the population parameter, like growth rate). We use a harvested single-species population model to integrate the effects of multiple threats on equilibrium abundance. Our results reveal that threats do not always display consistent additive behavior, even in simple systems. Instead, their additivity depends on the magnitudes of the impacts of two threats, and the population parameter that is impacted by each threat. In our model specifically, when multiple threats have a low impact on the growth rate of a population, they display superadditive dynamics. In contrast, threats that impact the species’ carrying capacity are always additive or subadditive. These dynamics can be understood by reference to the curvature of the relationship between a given population parameter (e.g., growth) and equilibrium population size. Our results suggest that management actions can achieve amplified benefits if they target low-amplitude threats that affect the growth rate, since these will be in a superadditive phase. More generally, our results suggest that cumulative impact theory should focus more than previously on the magnitude of the impact on the population parameter, and should be cautious about attributing additive dynamics to particular threat combinations.
机译：物种和生态系统通常面临不止一种威胁。这些多重威胁造成的损害可以非线性累积：或者当组合威胁的共同损害小于单独加在一起的两个威胁的损害时是亚加性的，或者当联合损害大于两个单独的损害加起来的总和时的超累加性。这些可加性动力学通常归因于威胁过程的性质，但是相互矛盾的经验观察对这一假设提出了挑战。在这里，我们使用理论模型来证明威胁的可加性会随着威胁影响的大小（威胁对人口参数的影响，例如增长率）的不同而发生变化。我们使用收获的单物种种群模型来整合多种威胁对均衡丰度的影响。我们的结果表明，即使在简单的系统中，威胁也不总是显示一致的累加行为。取而代之的是，它们的可加性取决于两种威胁的影响程度以及每种威胁所影响的总体参数。具体来说，在我们的模型中，当多种威胁对人口增长率的影响不大时，它们就会表现出超加和的动态。相比之下，影响物种承载能力的威胁总是加性的或次加性的。可以通过参考给定种群参数（例如，增长）和平衡种群规模之间关系的曲率来理解这些动态。我们的结果表明，如果管理措施针对影响增长率的低振幅威胁，则可以取得放大的收益，因为这些威胁将处于超加性阶段。更普遍地说，我们的结果表明，累积影响理论应比以前更加关注人口参数的影响幅度，并且在将累加动态归因于特定威胁组合时应保持谨慎。

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