CSIRO Ecosystem Sciences, Long Pocket Laboratories, Indooroopilly, Queensland 4068, Australia.
Nature. 2011 Feb 3;470(7332):86-9. doi: 10.1038/nature09735.
Suppression of the invasive plant Salvinia molesta by the salvinia weevil is an iconic example of successful biological control. However, in the billabongs (oxbow lakes) of Kakadu National Park, Australia, control is fitful and incomplete. By fitting a process-based nonlinear model to thirteen-year data sets from four billabongs, here we show that incomplete control can be explained by alternative stable states--one state in which salvinia is suppressed and the other in which salvinia escapes weevil control. The shifts between states are associated with annual flooding events. In some years, high water flow reduces weevil populations, allowing the shift from a controlled to an uncontrolled state; in other years, benign conditions for weevils promote the return shift to the controlled state. In most described ecological examples, transitions between alternative stable states are relatively rare, facilitated by slow-moving environmental changes, such as accumulated nutrient loading or climate change. The billabongs of Kakadu give a different manifestation of alternative stable states that generate complex and seemingly unpredictable dynamics. Because shifts between alternative stable states are stochastic, they present a potential management strategy to maximize effective biological control: when the domain of attraction to the state of salvinia control is approached, augmentation of the weevil population or reduction of the salvinia biomass may allow the lower state to trap the system.
抑制入侵植物满江红的水葫芦象甲是生物防治成功的标志性范例。然而，在澳大利亚卡卡杜国家公园的牛轭湖中，控制效果时好时坏并不完全。通过将一个基于过程的非线性模型拟合到来自四个牛轭湖的十三年数据集，我们在这里表明，不完全控制可以用两种稳定状态来解释——一种状态下满江红受到抑制，另一种状态下水葫芦逃脱象甲的控制。状态之间的转变与年度洪水事件有关。在某些年份，高水流会降低象甲的数量，从而导致从受控制状态向不受控制状态的转变；而在其他年份，有利于象甲的条件则促使其向受控制状态的转变。在大多数已描述的生态范例中，由于环境变化缓慢，如积累的养分负荷或气候变化，替代稳定状态之间的转变相对较少。而卡卡杜的牛轭湖则呈现出替代稳定状态的不同表现形式，产生了复杂且看似不可预测的动态。由于替代稳定状态之间的转变是随机的，因此它们提供了一种潜在的管理策略，可以最大限度地提高有效的生物控制效果：当接近满江红受控制状态的吸引域时，增加象甲的数量或减少满江红的生物量可能会使系统陷入较低的状态。
