Assessing ecological responses to environmental change using statistical models

Summary 1. There is a clear need to improve our ability to assess the ecological consequences of environmental change. Because of the complexity of ecosystems and a need to disentangle the effects of multiple pressures, predictions are often reliant on models and expert opinion. These require validation with observed data; in this respect, long-term datasets are particularly valuable. 2. Innovative statistical methods (nonparametric regression and additive models) are presented for identifying nonparametric ecological trends and changes in seasonality in response to environmental change. These are illustrated through the example of Loch Leven, a shallow freshwater lake. 35 years of monitoring data are examined spanning periods of enrichment, ecological recovery and changing climate. 3. Models are developed for phosphorus and nitrogen; temperature and rainfall; Daphnia grazers; and chlorophylla with the ecological objectives to examine trends in water quality and the corresponding trends in nutrient availability, grazer abundance and climate. 4. The analysis highlighted a generally decreasing availability of phosphorus over the study period and generally increasing nonparametric trends in nitrate concentrations and rainfall. Increasing spring temperatures were also evident as were significant nonparametric changes in summer grazer densities. 5. Significant reductions in spring and summer chlorophylla are highlighted, related to the return of Daphnia to the loch. However, no response in chorophylla is apparent to the later declining trends in phosphorus, but seasonality has changed. 6. Synthesis and applications. The analysis highlights the value of nonparametric statistical models for assessing complex ecological responses to environmental change. The models outlined can examine key ecological impacts of climate change, particularly effects on the timing of seasonal events and processes. The models are illustrated using long-term water quality data from Loch Leven to explore patterns in key environmental drivers and ecological responses affecting freshwater ecosystems. Analysis of chlorophylla in particular, highlighted the value of examining the seasonal trends separately, with different trends evident for winter and spring and a changing seasonal pattern.