DISSERTATION RESEARCH: Climate change and regime shifts

Yale University, New Haven CT

Investigators

Abstract

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.