Will tropical biodiversity dry up as a result of climate change? Two visions of the future

But Jeff Brawn, co-author of the book Global biology of change research, says birds are only part of the picture.

“Compared to a more optimistic future rainfall scenario, we predict that the business-as-usual scenario will be potentially disastrous for forest birds in the Neotropics. But really, in this study, we only use birds as an illustration. there will likely be similar threats to mammals, reptiles, amphibians, arthropods, fungi and plants, and the consequences for agriculture will also be significant,” said Brawn, professor emeritus in the Faculty of Natural Resources and Environmental Sciences at the College of Agriculture. Consumer and Environmental Sciences in Illinois.

Brawn and his colleagues previously analyzed the effects of longer dry seasons on 20 bird species in Panama and found significantly lower population growth rates for several species. Although this study used a solid 30-year dataset, he knew that 20 species was just a drop in the ocean. Would this formula work for all 3,000 species of birds that live in Neotropical forests?

Brawn teamed up with David Luther, an associate professor in the College of Science at George Mason University, and others, including Rong Fu of UCLA, to predict how precipitation will change in the Neotropics by 2100 under two climate scenarios. The business-as-usual scenario, known as SSP-8.5, represents a pessimistic view of the future without reducing carbon emissions. The team also created an SSP-2.6 impact model that reflects aggressive mitigation efforts and a rapid transition to a low-carbon economy.

Because birds already experience greater physiological and behavioral stress during dry periods – greater difficulty finding food, weight loss, delayed reproduction and higher mortality – the team focused specifically on how SSP-8.5 and SSP-2.6 could extend or shorten this season through all the time. region.

“Precipitation changes can have profound impacts on these systems, particularly with respect to biodiversity, but until recently temperature has dominated the climate change landscape,” Luther said. “Precipitation has been neglected for too long.”

By mapping projected changes in the length of the dry season in the Neotropical region – which includes Central America, the Caribbean and South America – the team then overlaid the distribution of approximately 3,000 species of forest birds to understand how their ranges might overlap with these changes.

“We managed to determine where the dry season will lengthen and where it will shorten, and to what extent and how many species currently living in these places will be affected. This included species that may be disproportionately affected because they are dead. anywhere else,” Luther said. “As a last resort, we overlaid a global layer of the world’s protected areas and saw whether they became significantly drier or wetter.”

The SSP-8.5 analysis predicts that the dry season will lengthen by at least 5% in three-quarters of neotropical lowland forests. The results show that these conditions will affect almost 2,000 species of birds living in the area. In contrast, in a more optimistic scenario, only 10% of lowland forests would dry out and just 90 bird species would be exposed to longer dry seasons.

Longer dry seasons can make it harder for birds to access food, breed and survive, but fewer rainy days can also have serious consequences for tropical ecosystems and species distributions at a more fundamental level.

“Think of a closed-canopy rainforest. If it gets too dry, there will be a threshold where it will open up and turn into a savannah,” Brawn said. “Many forest birds will not do well in savannahs, but savannah birds will do better. It is also possible that some closed-canopy forest species will do better in open forest. We don’t know how this will all turn out. outside.”

The maps show which areas will be most affected in both scenarios, but Luther says there is another way to interpret the maps.

“An equally important way to look at this issue is to focus on places that will be more stable in the future. “If we are to plan for future conservation efforts, we should put more effort into these areas because they are less likely to dry out. This will be particularly important for prioritizing existing protected areas and potentially establishing new ones,” he said. “I hope conservation organizations will take notice of this.”

Scientists hope that the minimal projected impacts under SSP-2.6 will motivate and accelerate policymakers’ action, but climate policy is only one piece of the puzzle.

“In any case, we paint a rosy picture in this newspaper because we do not take deforestation into account at all. If there are fewer trees, it’s warmer and drier,” Brawn said. “Unfortunately, thousands of hectares of tropical forest are disappearing every year, so the situation is more worrying.”

Luther adds: “The good news is that we can solve all this if we choose to. We can do the right thing.”