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。在湖泊生态系统中，物种之间现有相互作用变化的后果尤其重要，因为湖泊生态系统有可能在交替状态之间发生变化。湖泊通常是清澈的状态，几乎没有藻类生长，或者是浑浊的状态，经常有密集的藻类繁殖。有两个因素在很大程度上决定了一个湖泊是清澈还是浑浊，那就是营养物质和藻类的消耗者。营养物，尤其是氮和磷，会增加藻类的生长速度，导致藻华和浑浊状态。食藻者，特别是水蚤属，是非常有效的藻类食草动物，限制了它们的数量，促进了清澈的水状态。全球气温的上升缩短了冬季的长度和严酷程度，这增加了越冬水蚤的数量。本研究的重点是了解湖泊营养状况如何影响气候驱动的水蚤越冬差异。实验池塘将用于进行关键的实验，以确定浑浊和清澈的水状态之间的临界点在湖泊营养浓度和自然湖泊中看到的越冬水蚤丰度的范围内。确定导致生态系统状态转换的条件是气候变化下生态系统管理的重要组成部分。本研究将回答有关湖泊交替状态的基本问题，并为湖泊管理者促进湖泊的清澈状态提供有用的工具。这项研究的结果将发表在一本管理学期刊上；同时也是一份生态期刊，以确保它们能够接触到能够利用它们的受众。这项研究将确定在给定的营养水平下需要达到的水蚤密度，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.