Climate change is affecting ecosystems worldwide, including freshwater habitats, through shifts in precipitation and temperature. Temporary freshwater habitats, or those that dry for a portion of the year, are important homes to many aquatic organisms, including some amphibians.

Yet current understanding of how changes to temperature and patterns of drying affect freshwater organisms remains limited. In particular, changes to temperature and drying don’t happen in isolation – they often happen together.

To tackle some of these questions and further understand how aquatic organisms, which are already threatened in many cases, are affected by those simultaneous changes was the foundation of former Virginia Tech master’s student Elizabeth Shadle (biological sciences) and member of the Mims Lab at Virginia Tech.

The team's approach

The Virginia Tech team led by Shadle used an experimental approach to understand the effects of faster drying and warmer temperatures on the growth and survival of tadpoles (amphibian larvae) of two species common to the eastern United States, including Blacksburg: wood frogs (Lithobates sylvaticus) and spring peepers (Pseudacris crucifer). 

Shadle's findings were recently published in Freshwater Biology journal, with Virginia Tech co-authors William Hopkins, Lisa Belden, Mackenzi Hallmark, and Meryl Mims, all affiliated with the Global Change Center at the Fralin Life Sciences Institute.

Shadle led the 13-week experiment, with the help of a team of undergraduate researchers at Virginia Tech, over the spring and summer semesters in 2019. They used 48 experimental ponds, or “mesocosms”, with the same number of tadpoles in each, and modified warming, drying, in addition to both together, to examine how those two species react to faster drying and warmer freshwater habitats.

Elizabeth Shadle with members of the undergraduate research team along with Meryl Mims.
Elizabeth Shadle with her undergraduate research team and Meryl Mims, associate professor of biological sciences. Photo courtesy of Meryl Mims.

Key findings

  • The team found that warming temperatures shortened the time amphibians spend as tadpoles, with individuals metamorphosing into adults sooner. Additionally, drying resulted in smaller amphibians at metamorphosis. They didn’t find evidence of an interaction between warming and drying, indicating that warming and drying may affect amphibians independently and in unique ways.

  • They also expected that individuals that metamorphose faster should have smaller body size, which would indicate a tradeoff between speed of development (e.g., escape a “bad” pond sooner) and body size (e.g., possibly better fitness long-term). However, that’s not what the team found. Instead, faster developing amphibians also had larger body size. But this kind of “winner takes all” may be more common that we thought, and may point to complex outcomes of multiple effects of climate change.

  • Long term, this may mean to think carefully about making predictions when it comes to the effects of climate change on organisms with complex life cycles (for example, an aquatic and terrestrial life stage). This is particularly important as calls increase for simulations and advanced predictive models to understand possible consequences of climate change.