UC Davis

While individual populations wax and wane, aggregate community properties such as total biomass of organisms are often much less variable. The contrasting stability dynamics at the population and community levels have intrigued many ecologists to ask: (1) What are the underlying mechanisms maintaining long-term community stability despite the large variations in individual population size and in environmental conditions? (2) Will the mechanisms that historically undergird community stability become ineffective or even flip to destabilizing forces under changing climate? And (3) to what extent is fluctuating population dynamics chaotic in natural ecosystems? Here, I address these questions with data from freshwater ecosystems. In the first chapter, I show how climate change modifies the effectiveness of various stabilizing mechanisms—including their direction (stabilizing vs destabilizing) and strength using four-decade ecological observations in a dryland stream. In the second chapter, I focus on another stability mechanism—cross-ecosystem subsidies. Using two-year stable isotope measurements, I demonstrate the critical role of terrestrial detritus in maintaining food web stability and productivity of seasonal wetlands in two distinct and compensatory pathways. In the last chapter, I investigate whether chaos exists in lake ecosystems using time series analysis. I found evidence for high-dimension chaos in both daily and high-frequency Chlorophyll a data. The chaotic dynamics likely primarily arises from endogenous interactions within lake ecosystems.