Aquatic community responses to environmental change

One current challenge to ecologists is to develop informative ways of detecting subtle changes in the structure and function of ecosystems as they are perturbed by an expanding list of natural and human impacts. The impacts of global change (e.g., eutrophication, species invasion, climate warming) on freshwater ecosystems are widely recognized, but fundamental questions remain to be answered. The goal of my research proposal is to investigate the influence of global change on freshwater ecosystems and to explain the underlying mechanisms regulating the temporal variability in plankton. In particular, I will use time-series models to assess the impact of climate change and species invasion on the temporal dynamics among interacting species. Most of our understanding how ecosystems respond to environmental perturbations results from small-scale, short- term experiments. The analysis of long-term data sets provides a powerful tool to studying the impacts of environmental perturbations on ecosystem functions, to evaluate ecological indicators, and develop predictive models to forecast future changes. In the proposed research the time series data (over 40 years) that describe population dynamics of ~80 zooplankton species and ~300 phytoplankton species from Lake Washington, Seattle, USA will be used. In the first study, I will investigate how climate change alters the temporal variability in plankton. There is a strong climate signal over the last 40 years in Lake Washington: it is warmer now and the lake stratification period is about 30 days longer than it used to be. This long-term change in thermal conditions in the lake provides us with the opportunity to evaluate how communities respond to climate change using dynamic linear models. In a second study I evaluate whether climate change facilitate the invasion of Daphnia and how the increase of this invading taxon changed the plankton community and interactions among the component species. Daphnia spp. was absent in Lake Washington until the late 1970s and is now the most dominant crustacean. Finally, I will evaluate the relative impact of trophic and climate change on plankton. To test this, I will apply autoregressive time-series models to evaluate species interactions. The proposed studies will contribute to a better understanding of environmental perturbation impacts on lake ecosystems and provide knowledge needed for the management of the earth freshwater sources.