Hydra effects in stable communities and their implications for system dynamics
Hydra effects in stable communities and their implications for system dynamics
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DOI：
10.1890/15-0648.1
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发表时间：
2016-05-01
期刊：
影响因子：
4.8
通讯作者：
Abrams, Peter A.
中科院分区：
文献类型：
--
作者：
Cortez, Michael H.;Abrams, Peter A.
当一个物种的平均密度随着死亡率的增加而增加时，就会发生水螅效应。我们表明，在一个稳定的多物种系统中，一个物种表现出水螅效应，只有当保持该物种在其平衡密度不稳定的系统。原始系统的稳定性是由于水化效应物种对其他物种密度变化的响应。如果通过固定受水力影响的物种的密度来消除这种动态反馈，那么群落构成就会发生巨大变化（包括物种灭绝的可能性）。这一普遍结果有几个含义：（1）水螅效应发生在比以前描述的更广泛的物种和相互作用网络中，并且可能发生在多个物种中，甚至在小网络中;（2）捕食者引起水螅效应的条件（或疾病）往往不同于由其他死亡因素引起的疾病;（3）引入一种专门的或转换性的捕食者往往会引起群落的巨大变化，这往往涉及其他物种的灭绝;（4）试图维持一种水螅效应物种的恒定密度的捕捞政策可能难以实施，而且，如果成功，很可能导致其他物种密度的巨大变化;（5）水生生物的捕食者引起的营养级联和其他间接效应可表现出放大效应或意想不到的变化方向。虽然我们专注于最初稳定的系统和模型，没有阶段结构或性状的变化，我们的结果的一般性表明，类似的反应，死亡率将发生在许多系统没有这些简化的假设。此外，虽然水螅效应被定义为对死亡率变化的反应，但它们也意味着对移民和影响人口增长的其他参数变化的反直觉反应。
A hydra effect occurs when the mean density of a species increases in response to greater mortality. We show that, in a stable multispecies system, a species exhibits a hydra effect only if maintaining that species at its equilibrium density destabilizes the system. The stability of the original system is due to the responses of the hydra-effect species to changes in the other species' densities. If that dynamical feedback is removed by fixing the density of the hydra-effect species, large changes in the community make-up (including the possibility of species extinction) can occur. This general result has several implications: (1) Hydra effects occur in a much wider variety of species and interaction webs than has previously been described, and may occur for multiple species, even in small webs; (2) conditions for hydra effects caused by predators (or diseases) often differ from those caused by other mortality factors; (3) introducing a specialist or a switching predator of a hydra-effect species often causes large changes in the community, which frequently involve extinction of other species; (4) harvest policies that attempt to maintain a constant density of a hydra-effect species may be difficult to implement, and, if successful, are likely to cause large changes in the densities of other species; and (5) trophic cascades and other indirect effects caused by predators of hydra-effect species can exhibit amplification of effects or unexpected directions of change. Although we concentrate on systems that are originally stable and models with no stage-structure or trait variation, the generality of our result suggests that similar responses to mortality will occur in many systems without these simplifying assumptions. In addition, while hydra effects are defined as responses to altered mortality, they also imply counterintuitive responses to changes in immigration and other parameters affecting population growth.