An international team of researchers has carried out the most complete mapping of the predicted effects on anuran amphibians (toads, frogs and tree frogs) of the combination of more droughts and global warming. The study was published in the journal Nature Climate Change.
“Amazon and Atlantic Forest are the areas that have the most species and the greatest probability of drought events increasing, both in frequency, intensity or duration. This must harm the physiology and behavior of countless species. These biomes are among the regions on the planet with the greatest diversity of amphibians in the world, with many species that only occur in these locations”, says Rafael Bovo, researcher at the University of California, Riverside, in the United States, and one of the authors of the .
Most of the data, unprecedented for science until then, was collected by Bovo during his doctorate at the Institute of Biosciences at the Universidade Estadual Paulista (IB-Unesp), in Rio Claro, and his post-doctorate at the Institute of Biosciences at the University of São Paulo (IB-USP), both with a FAPESP scholarship.
The work is also part of the project “” , supported by FAPESP and coordinated by Carlos Navas, professor at IB-USP who also signed the study. Forecasts indicate that between 6.6% and 33.6% of anuran habitats will become more arid between 2080 and 2100, depending on greenhouse gas emissions by then. In a moderate emissions scenario, in which temperatures would increase by 2 ºC, 15.4% of these locations would be exposed to more droughts.
If emissions at the end of the century reach a high level, with warming of up to 4 ºC, more than a third (36%) of these habitats will be subjected to droughts that could be devastating for anuran amphibians, a group particularly sensitive to water loss. due to the thin and highly permeable skin.
In practice, in a 4 ºC warmer future, amphibians in the Amazon, Central America, Chile, northern United States and the European Mediterranean should experience an increase of more than four months per year in the frequency of droughts.
Even 2 ºC, however, is expected to increase the duration of droughts by between one and four consecutive months per year in most of the Americas, Europe, southern and central Africa and southern Australia.
Impact on reproduction
Researchers have found that some arid regions can even double the rates of water loss by toads, frogs and tree frogs. Just as the combination of drought and warming can also double the reduction in the activity time of these animals, compared to what is expected from the impact of warming alone.
“In an environment hotter and drier than the one they were evolutionarily adapted to live in, amphibians must reduce their time outside shelters to avoid heat and increased aridity, both of which accelerate water loss through evaporation. This also reduces the time spent feeding and searching for reproductive partners, which directly affects the viability of populations”, adds Bovo.
Biophysical simulations carried out by researchers showed, for example, that in the tropical part of the planet, which includes and part of , activity time is reduced in all climate scenarios throughout the year. While warming alone would reduce this time by 3.4% and drought alone by 21.7%, the combination of both would make animals spend 26% less time active.
In addition to the information collected in the field and laboratory by Bovo, another part of the data was gathered and standardized from existing scientific literature. The process lasted around three years.
The resulting database brings together both climate projections predicted for the end of the century across the planet and natural history information for a set of species. Among others, geographic distribution, use of microhabitats and presence of behavioral and physiological strategies to avoid water loss, such as posture or use of shelter to avoid exposing part of the body to the environment or secretion and spread of fluids on the skin, reducing evaporation .
In one, Bovo and collaborators showed how the thermal amplitude of anuran amphibians can vary even within the same species and how this can influence predictions of climate change impacts based only on thermal tolerance.
Researchers are now working to understand whether some species have enough plasticity to adjust to more arid environments in the short term, or even whether they are capable of adapting on an evolutionary scale, over thousands of years.
With this data, it will be possible to improve models for predicting local or regional extinctions of species, which could serve as a reference for other groups sensitive to increases in temperature and water availability.
“There are only three possible solutions for these species: to migrate, adapt or become extinct. We want to better understand which ones still have the capacity to adjust their physiology and behavior during life, or over generations, to survive such profound changes and predict what biodiversity will be left for us at the end of the century”, he concludes.
