Whole lake responses to species invasion mediated by climate change

湖泊生态系统面临多重压力，包括营养物质丰富、气候变化和非本土物种的入侵。后一种压力被广泛认为对世界各地的生物多样性和生态系统的功能产生了重大影响，其影响正在增加，因为人类活动提高了扩散速度，气候变化正在高纬度开辟新的生态位。温德米尔由两个盆地组成，是英格兰最大的湖泊，也是世界上研究最深入的湖泊之一，详细的记录可以追溯到70年前。在过去10至15年里，尽管污水处理厂继续去除一种关键的营养物质--磷，但水质仍明显恶化。例如，夏季藻类水华增加，深海氧气浓度下降。近年来，珍稀和受保护的北极鱼的数量也大幅下降。这些变化与低纬度非本土物种蟑螂的种群扩张相吻合。在这个项目中，我们将测试这样的假设，即蟑螂的扩张是有记录的温德米尔水域变暖的结果，以及种群的增加引发了一场‘营养级联’，导致对浮游动物更大的捕食，这反过来又减少了藻类对捕食者的控制。我们还将测试北极炭数量的下降是否是与蟑螂竞争的结果，因为两者都以浮游动物为食。我们在评估多重应激源的长期影响方面处于独特的地位，因为我们拥有丰富的生态和环境数据，并在上个世纪的大部分时间里从温德米尔收集了保存下来的样本。该项目将涉及对长期数据进行有针对性的详细分析，分析历史存档的鱼类和浮游动物样本，利用稳定同位素分析确定不同鱼类种群的食物来源和食物网结构，研究鱼的肠道内容物，进行水声分析以估计鱼的密度和位置，并建立模型以估计蟑螂生态位、浮游动物放牧和藻类生长。该项目涉及当前的一般生态问题，如自上而下控制的重要性、多种应激源的影响以及物种入侵可能导致的物种灭绝。研究结果也将与湖泊管理高度相关，因为如果我们的假设是正确的，那么面对气候变化和非本土物种入侵造成的食物链中断，养分去除将需要更加严格。

Lake ecosystems face multiple stresses including nutrient enrichment, climate change and invasion of nonindigenous species. This latter stress is widely recognised as having a major impact on biodiversity and the functioning of ecosystems worldwide and its effects are increasing because human activity has enhanced rates of dispersal and climate change is opening new niches at high latitudes. Windermere, comprising two basins, is England's largest lake and one of the best studied in the world with detailed records extending back for up to 70 years. A marked deterioration in water quality has been observed in the last 10 to 15 years despite continued removal of a key nutrient, phosphorus, at the wastewater treatment works. For example, summer algal blooms have increased and concentrations of oxygen at depth have decreased. The numbers of the rare and protected fish, the Arctic charr, have also declined dramatically in recent years. These changes have coincided with the population expansion of a lower-latitude, nonindigenous species, the roach. In this project we will test the hypotheses that the roach expansion is a result of the documented warmer waters in Windermere and that the population increase has triggered a 'trophic cascade' leading to greater predation on the zooplankton, which in turn has reduced the algae from control by their grazer. We will also test whether the decline in Arctic charr numbers results from competition with roach, since both feed on the zooplankton. We are in a unique position to assess the long term ramifications of multiple stressors because of the wealth ecological and environmental data and preserved samples collected from Windermere for most of the last century. The project will involve targeted, detailed analysis of the long-term data, analysis of the historical archived fish and zooplankton samples, identification of food sources of the different fish populations and food-web structure using stable isotope analysis and studies of fish gut contents, hydroacoustic analysis to estimate fish density and location and modelling to estimate roach ecological niche, zooplankton grazing and algal growth. The project is relevant to current general ecological issues such as the importance of top-down-control, the effects of multiple stressors and possible species extinction caused by species invasion. The results will also be highly relevant to the management of lakes since if our hypotheses are correct, nutrient removal will need to be even more stringent in the face of climate change and disruption of food-chains caused by invasion of nonindigenous species.