DISSERTATION RESEARCH: Climate change and regime shifts

了解气候变化如何改变物种之间的相互作用是当今生态学家面临的重大挑战之一。 物种之间现有相互作用的变化的后果在湖泊生态系统中特别重要，因为湖泊生态系统有可能在交替状态之间发生变化。 湖泊通常可以在清水状态下发现，几乎没有藻类生长，或者是浑浊的状态，其中经常有密集的藻类水华。 决定湖泊清澈或浑浊的两个主要因素是营养物质和藻类消费者。 营养物质，特别是氮和磷，会增加藻类的生长速度，导致藻华和浑浊状态。 藻类消费者，特别是水蚤属，是藻类的非常有效的食草动物，限制了它们的数量，促进了清澈的水状态。 全球气温的上升正在减少冬季的长度和严重程度，这增加了越冬水蚤的丰度。 本研究的重点是了解湖泊营养状况如何影响水蚤越冬的气候驱动的差异。 实验池塘将用于进行关键实验，以确定在浑浊和清澈的水状态之间的临界点是在整个湖泊营养浓度和越冬水蚤丰度的范围内看到的天然湖泊。确定引起生态系统状态之间转变的条件是气候变化下生态系统管理的一个重要组成部分。 该研究将回答湖泊交替状态的基本问题，并为湖泊管理者提供一个有用的工具，用于促进湖泊的清水状态。 这项研究的结果将发表在一个面向管理的杂志上;以及一个生态杂志，以确保他们达到可以利用它们的观众。 这项研究将确定在给定的营养水平下所需达到的水蚤密度，为湖泊管理者提供管理活动的目标，以保持美丽清澈的湖泊。 此外，该项目将为一名本科生提供科学研究方面的培训和指导。

Understanding how climate change alters interactions among species is one of the big challenges facing ecologists today. The consequences of changes to existing interactions among species are especially important in lake ecosystems where there is the potential for shifts between alternate states. Lakes often can be found in either a clear-water state with little algal growth, or a turbid state in which there are frequent dense algal blooms. Two factors which largely determine whether a lake will be clear or turbid are nutrients and algal consumers. Nutrients, especially nitrogen and phosphorus, increase the growth rate of algae leading to algal blooms and a turbid state. Algal consumers, particularly of the genus Daphna, are very effective grazers of algae, limiting their populations and promoting the clear-water state. The increase in global temperatures is decreasing the length and severity of winters, which increases the abundance of over-wintering Daphnia. This study focuses on understanding how lake nutrient status affects the climate driven differences in over-wintering of Daphnia. Experimental ponds will be used to perform the critical experiment to determine where the tipping point between a turbid and a clear-water state is across the range of lake nutrient concentrations and overwintering Daphnia abundance seen in natural lakes. Determining the conditions that bring about shifts between ecosystem states is an important part of the management of ecosystems under a changing climate. This research will answer fundamental questions about alternate states in lakes and provide a useful tool for lake managers to use for promoting the clear-water state in lakes. Results of this study will be published in a management oriented journal; as well an ecological journal to ensure they reach the audience that can make use of them. This study will determine the densities of Daphnia required to be achieved for a given nutrient level, providing lake managers with targets for their management activities to maintain beautiful clear lakes. Additionally, this project will provide an undergraduate student with training and mentoring in the conduct of scientific research.