Thermal tolerance and the response of freshwater communities to multiple stressors

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Canadians are the stewards of more inland water bodies than any other country in the world, a unique resource we have committed to preserve via the Canada water act. Yet, freshwater ecosystems face a number of threats that include pollution linked to watershed land use, and warming waters due to directional climate change and more frequent heat waves. Predicting impacts of these threats on freshwater biodiversity requires an assessment of their interactive effects, namely their impact when acting individually and when acting in combination. My research program will disentangle the interactive effects of climate warming and agricultural pollution on freshwater animals (plankton and fish) in Canada. My previous research has shown that agricultural pollution causes widespread ecological and evolutionary effects in freshwater ecosystems, with communities gaining and losing species and with populations evolving (changing their traits) in response to watershed land use. I will now ask whether these changes make communities more or less tolerant of a warming climate. My research program is centered around three objectives. First, using a 'big data' approach, my team will estimate the thermal tolerance of hundreds of species of lake plankton and fish. We will then use two large standardized surveys of zooplankton (664 lakes across Canada) and fish (768 lakes in Québec) from lakes that differ in watershed land use (from pristine to highly agricultural) and quantify the 'mean thermal tolerance' of animals in these lakes. Second, we will rely on a state-of-the-art experimental facility to expose plankton communities to agricultural pollution in 98 experimental ponds. We will conduct a unique large-scale experiment, exposing plankton to two gradients of agricultural pollution based on field data. We will track ecological and evolutionary responses, and then expose communities to an experimental but realistic heat wave event to test whether pollution influenced thermal tolerance. Finally, we will sample zooplankton and fish from lakes that differ in watershed land use and measure their thermal tolerance with established physiological assays. This will allow us to determine whether populations (of the same species) found in pristine vs. polluted sites differ in their thermal tolerance. As a whole, this program will assess whether agricultural land use and climate change are likely to have additive or interactive (antagonistic or synergistic) effects on lake animals. This information will allow us to better predict and manage biodiversity change in Canadian lakes facing a warming climate and intensifying agriculture in their watersheds.