A paleolimnological analysis of the hierarchy of environmental controls on the resilience of aquatic communities in Yellowstone National Park, USA

An ecosystem’s ability to maintain structure and function during disturbance, defined as resilience, is influenced by a hierarchy of environmental controls. Climate exerts a first-order level of control by influencing water column thermal structure, catchment vegetation, and precipitation seasonality; these in turn exert lower-order levels of control on biological community composition and productivity. This dissertation examines lacustrine sediment records of the response of aquatic communities to climate and trophic cascades in Yellowstone National Park. It also uses Yellowstone as a model system in a role-playing game to teach the complexity of environmental and human dimensions in management decisions in an undergraduate classroom. A 20th Century valve size diminution trend in the diatom genus Cyclotella has been observed in many Northern Hemisphere lakes and attributed to warmer temperatures with a consequent influence on lake thermal structure. This study explored whether a similar size diminution trend is evident in the fossil record of the Holocene Insolation Maximum and did not find the predicted trend. Instead, many species exhibited increasing cell size over time, likely responding to water column thermal structure and nutrient availability. During the 20th century, fish were stocked in naturally fishless lakes. This study reconstructed the impacts of fish stocking on trophic structure as recorded by diatom and zooplankton assemblages and the trophic function as reflected by proxies of primary and secondary productivity. Overall, the sediment records did not exhibit a distinct response to fish stocking. Instead, a shift to dominance by benthic diatom species began in the interval of 1935-1950, which suggests lower lake levels resulting from warmer, drier climatic conditions. Thus, climate likely had a more prominent influence on diatom community structure than did manipulation of the fish community. A role-playing game was created and assessed as an authentic performance task in an undergraduate biogeography class. Student players assumed the roles of stakeholders and worked together to reconcile habitat requirements of grizzly bears, human dimensions, and external environmental issues to design a habitat bridge for grizzly bears in Montana. The game emphasized the challenges of the decision making process and the importance of communication