High-amplitude fluctuations and alternative dynamical states of midges in Lake Myvatn
High-amplitude fluctuations and alternative dynamical states of midges in Lake Myvatn
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DOI：
10.1038/nature06610
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发表时间：
2008-03-06
期刊：
影响因子：
64.8
通讯作者：
Gardarsson, Arnthor
中科院分区：
文献类型：
--
作者：
Ives, Anthony R.;Einarsson, Arni;Gardarsson, Arnthor
复杂的动力学通常由简单的生态模型（1，2）显示，并已在实验室（3，4）和自然系统（5-9）中得到明确证明。然而，许多理论上可能的动力学在自然界中仍然缺乏文献记载。在这里，我们研究了长期的时间序列数据，摇蚊，Tanytarsus gracilentus（双翅目：摇蚊科），在湖Myvatn，冰岛。吸浆虫的密度波动几乎有六个数量级。然而，这些波动不是有规律的周期，而是4 - 7年的不规则周期，表明动态复杂。我们适合三个消费者资源模型能够定性不同的动态数据。其中，最佳拟合模型在没有环境变化的情况下显示了替代的动态状态;根据初始的蠓密度，该模型显示了围绕固定点的波动或高振幅周期。这解释了观察到的复杂的种群动态：高振幅但不规则的波动发生，因为随机变异性导致动态之间的吸引域切换到替代状态。在该模型中，波动的幅度强烈依赖于分钟的资源补贴到吸浆虫栖息地。这些资源补贴可能对人类引起的湖泊水文变化很敏感，人类的影响，如疏浚，导致更高幅度的波动。Tanytarsus gracilentus是Myvatn生态系统的关键组成部分，代表湖泊次级生产力的三分之二（10），并为鱼类和繁殖鸟类种群提供重要的食物资源（11，12）。因此，由交替的动态状态产生的高振幅、不规则的摇蚊密度波动主导了湖泊的大部分生态。
Complex dynamics are often shown by simple ecological models(1,2) and have been clearly demonstrated in laboratory(3,4) and natural systems(5-9). Yet many classes of theoretically possible dynamics are still poorly documented in nature. Here we study long- term time- series data of a midge, Tanytarsus gracilentus ( Diptera: Chironomidae), in Lake Myvatn, Iceland. The midge undergoes density fluctuations of almost six orders of magnitude. Rather than regular cycles, however, these fluctuations have irregular periods of 4 - 7 years, indicating complex dynamics. We fit three consumer - resource models capable of qualitatively distinct dynamics to the data. Of these, the best- fitting model shows alternative dynamical states in the absence of environmental variability; depending on the initial midge densities, the model shows either fluctuations around a fixed point or high- amplitude cycles. This explains the observed complex population dynamics: high-amplitude but irregular fluctuations occur because stochastic variability causes the dynamics to switch between domains of attraction to the alternative states. In the model, the amplitude of fluctuations depends strongly on minute resource subsidies into the midge habitat. These resource subsidies may be sensitive to human- caused changes in the hydrology of the lake, with human impacts such as dredging leading to higher- amplitude fluctuations. Tanytarsus gracilentus is a key component of the Myvatn ecosystem, representing two- thirds of the secondary productivity of the lake(10) and providing vital food resources to fish and to breeding bird populations(11,12). Therefore the high- amplitude, irregular fluctuations in midge densities generated by alternative dynamical states dominate much of the ecology of the lake.