Hexbyte Glen Cove Amazon Rainforest birds’ bodies transform due to climate change

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Measuring wing length of a Thrush-like Antpitta (Myrmothera campanisona). Credit: Vitek Jirinec

The most pristine parts of the Amazon rainforest devoid of direct human contact are being impacted by human-induced climate change, according to new research by LSU scientists. New analyses of data collected over the past four decades show that not only has the number of sensitive resident birds throughout the Amazon rainforest declined, but the body size and wing length have changed for most studied species. These physical changes in the birds track increasingly hot and dry conditions in the dry season, from June to November.

“Even in the middle of this pristine Amazon rainforest, we are seeing the global effects of caused by people, including us,” said Vitek Jirinec, LSU alumnus (Ph.D. ’21), associate ecologist at the Integral Ecology Research Center and lead author to this study published in the journal Science Advances.

Birds in the Amazon rainforest have become smaller and their wings have become longer over several generations, indicating a response to the shifting that may include new physiological or nutritional challenges.

This is the first study to discover these changes in non- and shape, which eliminates other factors that may have influenced these physiological changes. Jirinec and colleagues studied data collected on more than 15,000 individual birds that were captured, measured, weighed, marked with a leg band and released, over 40 years of field work in the world’s largest rainforest. The data reveal that nearly all of the birds’ bodies have reduced in mass, or become lighter, since the 1980s. Most of the lost on average about 2 percent of their body weight every decade. For an average bird species that weighed about 30 grams in the 1980s, the population now averages about 27.6 grams. How significant is this?

“These birds don’t vary that much in size. They are fairly fine-tuned, so when everyone in the population is a couple of grams smaller, it’s significant,” said co-author Philip Stouffer, who is the Lee F. Mason Professor in the LSU School of Renewable Natural Resources.

The data set covers a large range of the rainforest so the changes in the birds’ bodies and wings across communities are not tied to one specific site, which means that the phenomenon is pervasive.

“This is undoubtedly happening all over and probably not just with birds,” Stouffer said. “If you look out your window, and consider what you’re seeing out there, the conditions are not what they were 40 years ago and it’s very likely plants and animals are responding to those changes as well. We have this idea that the things we see are fixed in time, but if these birds aren’t fixed in time, that may not be true.”

The scientists investigated 77 species of rainforest birds that live from the cool, dark forest floor to the warmer, sunlit midstory. They discovered that the birds that reside in the highest section of the midstory and are the most exposed to heat and drier conditions, had the most dramatic change in body weight and wing size. These birds also tend to fly more than the birds that live on the forest floor. The idea is that these birds have adapted to a hotter, drier climate by reducing their wing loading therefore becoming more energy efficient in flight. Think of a fighter jet with a heavy body and short wings that requires a lot of energy to fly fast compared to a glider plane with a slim body and long wings that can soar with less energy. If a bird has a higher wing loading, it needs to flap its wings faster to stay aloft, which requires more energy and produces more metabolic heat. Reducing and increasing wing length leads to more efficient resource use while also keeping cooler in a warming climate.

LSU alumnus Ryan Burner (Ph.D. ’19) conducted much of the analysis that revealed the variation among the groups of birds over the years. Burner, who is now a research wildlife biologist at the U.S. Geological Survey Upper Midwest Environmental Sciences Center, is the second author of this study.

The question of the future capacity of Amazonian to deal with increasingly hotter and drier surroundings, especially in the dry season, remains unanswered. The same question can be asked for a lot of places and species that live at the edges of even more environmental extremes.

“There may be other researchers in other places who have relevant data from the 1970s and 1980s that could be compared to modern data, because the bird banding protocol we used is pretty standard. So if you measure mass and wing, maybe there will be more datasets that will emerge and we’ll be able to get more of an idea of the variation across space and how it might be changing in different systems,” Stouffer said.

More information:
Vitek Jirinec, Morphological consequences of climate change for resident birds in intact Amazonian rainforest, Science Advances (2021). DOI: 10.1126/sciadv.abk1743. www.science.org/doi/10.1126/sciadv.abk1743

Amazon Rainforest birds’ bodies transform due to climate change (2021, November 12)
retrieved 14 November 2021

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Hexbyte Glen Cove Some Amazon rainforest regions more resistant to climate change than previously thought thumbnail

Hexbyte Glen Cove Some Amazon rainforest regions more resistant to climate change than previously thought

Hexbyte Glen Cove

Photo was taken from the top of the K34 flux tower site located 60km north of Manaus, Brazil. Credit: Xi Yang/University of Virginia

Forests can help mitigate climate change, by taking in carbon dioxide during photosynthesis and storing it in their biomass (tree trunks, roots, etc.). In fact, forests currently take in around 25-30% of our human-generated carbon dioxide (CO2) emissions. Certain rainforest regions, such as the Amazon, store more carbon in their biomass than any other ecosystem or forest but when forests become water-stressed (not enough water in the soil, and/or air is extremely dry), forests will slow down or stop photosynthesis. This leaves more CO2 in the atmosphere, and can also lead to tree mortality.

The current Earth system models used for climate predictions show that the Amazon rainforest is very sensitive to stress. Since the air in the future is predicted to get warmer and drier with climate change, translating to increased water stress, this could have large implications not just for the ‘s survival, but also for its storage of CO2. If the forest is not able to survive in its current capacity, climate change could greatly accelerate.

Columbia Engineering researchers decided to investigate whether this was true, whether these forests are really as sensitive to water stress as what the models have been showing. In a study published today in Science Advances, they report their discovery that these models have been largely over-estimating water stress in .

The team found that, while models show that increases in air dryness greatly diminish rates in certain regions of the Amazon rainforest, the observational data results show the opposite: in certain very wet regions, the forests instead even increase photosynthesis rates in response to drier air.

“To our knowledge, this is the first basin-wide study to demonstrate how—contrary to what models are showing—photosynthesis is in fact increasing in some of the very wet regions of the Amazon rainforest during limited water stress,” said Pierre Gentine, associate professor of earth and environmental engineering and of earth and environmental sciences and affiliated with the Earth Institute. “This increase is linked to atmospheric dryness in addition to radiation and can be largely explained by changes in the photosynthetic capacity of the canopy. As the trees become stressed, they generate more efficient leaves that can more than compensate for water stress.”

Gentine and his former Ph.D. student Julia Green used data from the Intergovernmental Panel on Climate Change’s Coupled Model Intercomparison Project 5 (CMIP5) models and combined them with machine learning techniques to determine what the modeled sensitivity of photosynthesis in the tropical regions of the Americas was to both soil moisture and air dryness. They then performed a similar analysis, this time using observational remote sensing data from satellites in place of the data, to see how the observational sensitivity compared. To relate their results to smaller-scale processes that could explain them, the team then used flux tower data to understand their results at the canopy and leaf level.

Earlier studies have shown that there are increases in greenness in the Amazon basin at the end of the dry season, when both the soil and air is drier, and some have linked this to increases in photosynthesis. “But before our study, it was still unclear whether these results translated to an effect over a larger region, and they had never been connected to air dryness in addition to light,” Green, who is now a postdoctoral research associate at Le Laboratoire des Sciences du Climat et de l’Environnement in France, explained. “Our results mean that the current models are overestimating carbon losses in the Amazon rainforest due to climate change. Thus, in this particular region, these forests may in fact be able to sustain photosynthesis rates, or even increase it, with some warming and drying in the future.”

Gentine and Green note, however, that this sensitivity was determined using only existing data and, if dryness levels were to increase to levels that are not currently being observed, this could in fact change. Indeed, the researchers found a tipping point for the most severe dryness stress episodes where the forest could not maintain its level of photosynthesis. So, say Gentine and Green, “our findings are certainly not an excuse to not reduce our carbon emissions.”

Gentine and Green are continuing to look at themes related to vegetation water stress in the tropics. Green is currently focusing on developing a water indicator using remote sensing data (a dataset that can be used to identify when a forest is under stressful conditions), quantifying the effects of on plant carbon uptake, and relating them to ecosystem traits.

“So much of the scientific research coming out these days is that with , our current ecosystems might not be able to survive, potentially leading to the acceleration of global warming due to feedbacks,” Green added. “It was nice to see that maybe some of our estimates of approaching mortality in the Amazon rainforest may not be quite as dire as we previously thought.”

The study is titled “Amazon rainforest photosynthesis increases in response to atmospheric dryness.”

More information:
J.K. Green el al., “Amazon rainforest photosynthesis increases in response to atmospheric dryness,” Science Advances (2020). advances.sciencemag.org/lookup … .1126/sciadv.abb7232

Some Amazon rainforest regions more resistant to climate change than previously thought (2020, November 20)

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