Disturbance-driven changes in ecosystem variability: a new tool for understanding ecological dynamics

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Statistics teaches us that all variables can be initially characterized by two parameters - their central tendency and their variability. Both impart meaningful information about the distribution of a response variable and thus provide a foundation for inference, prediction, and theory. However, variance is seldom considered in ecological studies as a response of interest. As a result, little is known about the functional importance of, or the mechanistic basis for, changes in the variance of ecosystem dynamics. Disturbances have the potential to affect all aspects of ecosystems, from species diversity to structure and function, by generating significant spatial and temporal heterogeneity that can profoundly alter system dynamics. Defined by their frequency, severity, and extent, disturbances can directly or indirectly contribute to changes in variability. Examining how a disturbance alters variance can reveal ecological change that might otherwise be overlooked and may also suggest the underlying mechanisms that produce such dynamics. Building on previous work, I use freshwater lakes, with complex multi-dimensional habitat structure, well-delineated ecosystem boundaries and multiple trophic levels with rapid generation times as ideal candidates for modelling and experimentation. The current proposal will test disturbance-variance predictions across multiple temporal and spatial scales: 1) among lakes with large “system-wide” disturbances occurring annually over decades; 2) within lakes (and years) with different mixing frequencies (i.e., disturbance regimes) and stressor regimes; and 3) experimentally, using mesocosms to test predictions arising from different disturbance regimes. Increasing variance has been identified as an indicator of state change and I will also assess the utility of using variance as an early warning metric and a tool to trigger management and mitigation activities. In a world where multiple stressors are now the norm rather than the exception and increased variability further reduces our chances of detecting their effects, developing a predictive understanding of the response of ecosystem variability to disturbance is an imperative. Lakes are of critical importance to human well-being and many of the threats to freshwater ecosystems globally (e.g., climate warming, nutrients), are readily observed and documented in the long-term and high-frequency datasets captured by long-term monitoring program. These projects will explore the most important attributes of both disturbance and ecosystem variability and will ultimately improve our ability to manage our freshwater resources.This initiative will draw on the best of both worlds to collaboratively train 2 Ph.D., 1 M.Sc. and 2 undergraduates with involvement from a top university-based limnological laboratory as well as a pre-eminent provincial government freshwater research centre.