Estimating the Direct and Indirect Impacts of Climate Change On Small Wetland Ecosystems

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The Intergovernmental Panel on Climate Change released a report in 2018 estimating the consequences of the 1.5o C increase in temperature that we are almost certain to see in the next 25 years. The evidence is unequivocal that our climate is changing, that the changes are caused by human activities and the economic and social consequences will be large and negative. Mitigation of climate change impacts is going to require reasonably accurate predictions of the effects of climate change over the next 30-100 years. Changes in temperature and precipitation are likely to have both direct and indirect impacts on small wetland communities. Direct impacts are caused by pushing some organisms outside the range of temperatures or hydro-period where they can thrive or persist and indirect impacts are caused by changing biological interactions among species within aquatic systems. One example of such a potential indirect effect caused by changes in interactions, is between green frog and wood frog tadpoles. Green frogs and wood frogs benefit from the direct effect of deeper, longer lasting ponds due to increased precipitation because they are less likely to undergo mortality as a result of pond drying. However, the beneficial effect on wood frogs of increased hydro-period may be offset or overwhelmed by increased consumption of wood frog eggs by green frog tadpoles or increased transmission of Rana virus from green frog larvae to wood frog larvae. The Houlahan lab at the University of New Brunswick in Saint John will use wood frogs in natural ponds as a model system supplemented by laboratory experiments and observations of unmanipulated systems, to examine the direct and indirect effects of warming. We will increase the temperature of six natural ponds at the Long-term Experimental Wetlands Area on CFB Gagetown in New Brunswick by ~ 6 degrees C using solar panel heating units and polyethylene tubing. Each of the manipulated ponds will be paired with a similar control pond. We will measure wood frog growth, development, survival, amphibian disease prevalence and virulence, and green frog and dragonfly larval abundance in treatment and control ponds. We will build predictive models describing the direct impacts of temperature on wood frog growth, development and survival and indirect impacts through effects of warming on wood frog predators such as green frogs and dragon fly larvae, and wood frog diseases such as chytridiomycosis and Rana virus. These predictive models will be used by policymakers and conservation professionals to develop policies and strategies to mitigate climate change impacts in natural systems.