The effects of experimental wetland warming and drying on subarctic wood frogs
Freshwater ecosystems are predicted to be heavily impacted by climate change over the next century. These temperature increases are expected to disproportionally affect temporary wetlands and polar ecosystems. Current research on climate-related impacts in polar regions has primarily focused on fishes and aquatic invertebrates. However, other polar freshwater organisms, such as amphibians, are sensitive to environmental change and will likely be strongly affected by climate change. For example, changes in air temperature could affect larval amphibian growth and survival through both increases in water temperature and decreases in wetland hydroperiod.
In order to evaluate the effects of wetland warming and drying on growth and survival of larval amphibians, we conducted an experiment in 378-L experimental wetlands with wood frogs (Rana sylvatica) located at Churchill, Manitoba, Canada. We fully crossed three warming treatments (ambient temperature, +1°C, +2°C) with three drying treatments (fast, moderate, semi-permanent) and measured survival, size at, and time to metamorphosis. Each wetland was stocked with 25 wood frog tadpoles (Gosner stage = 25) and also received 100 g of dried sedge added to filtered lake water.
The proportion of wood frogs that survived to metamorphosis increased with warming temperature and wetland hydroperiod. The effect of wetland drying was independent of the effect of wetland warming. Size at metamorphosis was not affected by drying or warming treatment. Wood frogs did respond wetland drying by emerging earlier from fast-drying wetlands. Warming also affected wood frog time to metamorphosis with the +2°C treatments producing the earliest metamorphs.
Our results suggest the effects of future temperature increases on wood frogs will be complex. While our results show larval wood frogs from the subarctic have some capacity to accelerate their developmental rate in response to environmental change, it is uncertain if their response will be enough to offset a net reduction in survival. Overall, our experiment provides a significant advancement in understanding how polar amphibians will respond to future climate change.