An international team of researchers has completed the most comprehensive survey ever of the predicted planetwide effects of drought and global warming on anurans (frogs and toads). An article reporting their findings is published in the journal Nature Climate Change.
"The Amazon and the Atlantic Rainforest are the biomes with the most anuran species and the highest probability of an increase in both the frequency and intensity or duration of drought events. This will be harmful to the physiology and behavior of countless species. These biomes are among the regions of the planet with the greatest diversity of amphibians. Many species only occur in these places," said Rafael Bovo , a researcher at the University of California, Riverside (USA), and one of the authors of the article.
The raw data used in the study had never previously been collected by any scientist. Most of the data was assembled by Bovo during research he conducted in Brazil with a scholarship from FAPESP, more precisely for his doctorate at São Paulo State University's Institute of Biosciences (IB-UNESP) in Rio Claro, and for postdoctoral studies at the University of São Paulo's Institute of Biosciences (IB-USP).
The research was also part of the Thematic Project "Impacts of climate/environmental change on fauna: an integrative approach" , supported by FAPESP and coordinated by Carlos Navas , full professor at IB-USP and penultimate author of the article.
The findings include a prediction that between 6.6% and 33.6% of anuran habitats will become arid by the period 2080-2100, depending on the level of greenhouse gas emissions from now on. If greenhouse gas emissions rise moderately and global warming increases by 2 °C, 15.4% of these habitats will be exposed to more drought events.
If greenhouse gas emissions reach a high level by the end of this century and global warming increases by 4 °C, more than a third (36%) of these habitats will suffer from drought events that may be devastating for anurans, which are particularly sensitive to water loss owing to their thin, highly permeable skin.
In practice, in a future world 4 °C warmer, anurans in the Amazon, Central America, Chile, the northern U.S. and the European Mediterranean are predicted to experience drought events lasting an additional four months per year.
Even 2 °C warming, however, will increase the duration of droughts by one to four consecutive months per year in most of the Americas, Europe, southern and central Africa, and southern Australia.
Combination
The researchers concluded that frogs and toads may experience twice the rate of water loss in some arid regions and that the combination of drier weather and higher temperatures may double the reduction in anuran activity compared with the expected impact of warming alone.
"In a hotter and drier environment than the one they've adapted to in their evolutionary history, anurans will have to spend less time outside their shelters to avoid the heat and dryness, both of which accelerate evaporative water loss. As a result, they will also have to spend less time foraging and finding mates for reproduction, which will directly affect the viability of these populations," Bovo said.
Biophysical simulations performed by the researchers showed, for example, that anurans will spend less time in activity in tropical regions of the planet, including the Amazon and part of the Atlantic Rainforest biome, under all climate scenarios throughout the year. While warming alone and drought alone will decrease activity hours by 3.4% and 21.7% respectively, the combination of warming and drought will decrease activity hours by 26%.
Besides the data collected in the field and in the lab by Bovo, the survey also gleaned and standardized information from the scientific literature. The process lasted about three years.
The resulting database comprises both planetwide climate forecasts for the end of the century and information on the natural history of 6,416 species listed as "threatened" by the International Union for Conservation (IUCN). The variables analyzed by the researchers included geographical distribution, use of microhabitats, and presence of behavioral and physiological strategies to avoid water loss, such as posture, burrowing to shelter from environmental pressure, secretion, or waterproofing via cutaneous surface fluid or lipids, for example.
In a previous article , Bovo and collaborators showed how thermal breadth in frogs and toads may vary even within species, and how this can influence predictions of the impact of climate change based solely on thermal tolerance.
The researchers are now focusing on understanding whether some species have sufficient plasticity to adjust relatively quickly to a drier environment and whether they are able to adapt over an evolutionary scale of thousands of years. The long-term goal is to refine the models on which predictions of local or regional species extinction are based, enabling their use as benchmarks for other animal groups that are sensitive to warming and water scarcity.
"There are only two possible solutions for anurans to avoid extinction: migration or adaptation. We want to develop a deeper understanding of which species still have the ability to adjust their physiology and behavior, in a single lifetime or over several generations, so as to survive these profound changes, and to help predict the magnitude of the biodiversity that will remain at the end of the century," Bovo said.
About FAPESP
The São Paulo Research Foundation (FAPESP) is a public institution with the mission of supporting scientific research in all fields of knowledge by awarding scholarships, fellowships and grants to investigators linked with higher education and research institutions in the state of São Paulo, Brazil. FAPESP is aware that the very best research can only be done by working with the best researchers internationally. Therefore, it has established partnerships with funding agencies, higher education, private companies, and research organizations in other countries known for the quality of their research and has been encouraging scientists funded by its grants to further develop their international collaboration.
