Alternative stable states explain unpredictable biological control of Salvinia molesta in Kakadu

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.     

正视电子游戏

<正>吴宇森,蜚声世界影坛的艺术巨匠,第一位在好莱坞星光大道留下印记的华人导演。他常常被人们称为"暴力美学大师",而暴力美学也是吴氏电影的独有标签。暴力?美学?两者竟然能合二为一?是的,两个看似毫无关联的事物的确能这样有机地结合在一起。名著?电子游戏?更没问题!国人必读的"四大名著",每一本都被搬上了游戏的舞台,而且还有不少中国文学作品被国外的游戏公司反复制作。当然,也有不少经典的电子游戏作品,经过拍摄制作成了电