As the Academy celebrates biodiversity — the remarkable, beautiful tapestry of life on Earth — this year, we are delving into some of the fascinating locations our scientists have visited in the region and across the globe to study and help protect our planet’s phenomenally diverse and incredible species.
The Amazon Rainforest
Few places are as evocative of biodiversity as the Amazon Rainforest, a region of South America that occupies just 0.5% of Earth’s terrestrial area yet harbors a disproportionately astounding 10% of known species diversity. Roughly 1,300 bird species call the Amazon Rainforest their home, as do more than 3,000 species of fishes and countless primates, butterflies, orchids, frogs and more.
In some locations, the Amazon Rainforest is one of the last remaining truly wild places, with only minimal signs of the industrialized world — though this is rapidly changing. How the Amazon accumulated this impressive list of organisms remains one of the great mysteries of modern biology, one that continues to be debated by scientists who work across many disciplines.
The region also has a major impact on the rest of the planet. By some estimates, the Amazon Rainforest contains as many as 13% of all the individual trees on the planet — making it one of Earth’s most crucial carbon sinks. Its vegetation stores a mind-boggling 120 billion metric tons of carbon in its stems, leaves, trunks and branches — a reduction, however, from what it has historically stored — but still a truly impressive number. Moreover, studies have shown that the Amazon Rainforest creates its own climate, which can then affect those of other regions as far away as the North American Pacific Northwest.
The Amazon River
The Amazon Rainforest is home to the longest river on Earth that originates high in the Andes mountains as glacial melt and then crosses the entire continent to drain into the Atlantic Ocean. The Amazon River’s basin is made up of an intricately interconnected web of tributaries that drain more water than the next seven largest river basins combined.
This web of rivers has a known effect on some Amazonian birds and primates. Large rivers like this one — some ten miles across at their widest point — can isolate populations of these species, which then evolve differences on either side and form new species. Indeed, whole communities of organisms are known to become unique across these rivers, a pattern that was known by Indigenous groups in the area long before the arrival of Europeans.
Academy Ornithologist and Postdoctoral Researcher Lukas Musher, PhD recently led a scientific expedition to a relatively small Roosevelt River to study the effects these bodies of water have on the genetics of various bird species in the area. The group recently published a paper on their findings that was also covered in WIRED and Quanta Magazine.
Nearly a century prior, the river’s namesake, Teddy Roosevelt, along with Brazilian statesman Candido Mariano de Silva Rondon and a crew of men charted the river to find where it met the Amazon on a harrowing, months-long journey that nearly cost Roosevelt his life.
Musher’s expedition was not quite as grueling as Teddy’s but did reward the researchers with new scientific discoveries. By collecting specimens of uncommon birds on both banks of the Roosevelt River, they found evidence that different bird species may be nearly identical on either bank of a river, but their genetics suggest they are divergent.
Birds of a Feather
One of these collected bird species was the Gray Antwren (Myrmotherula menetriesii). Gray Antwrens are small birds — no more than about 4 inches from head to tail — that feed on a variety of arthropods as they forage in mixed-species flocks within the forest midstory. Through this fieldwork, Musher and his colleagues found they actually differ on either side of the Roosevelt River.
The Rufous-necked Puffbird (Malacoptila rufa), is another species found across the southern Amazon Rainforest from Peru to the mouth of the Amazon River. Musher’s group compared the genomes of these birds from both sides of the river and found that they, like the antwrens, are evolving separately on opposite banks, even though they show relatively few differences in their plumage.
Musher says, “Many people immediately wonder: if birds can fly, why don’t they just fly across rivers, especially a small one like Rio Roosevelt?” The answer, he explains, is rather simple. While many species of birds do fly back and forth across even the largest rivers with little effort, like the powerful predator Harpy Eagle, many other species of rainforest birds are weak flyers. These particular birds know their limitations and often don’t like to travel out of the forest to cross a large body of moving water. A variety of scientific studies have shown this to be the case.
The Future of the Region’s Biodiversity
The scientific view of how rivers affect biodiversity is rapidly changing and continues to be debated. As these rivers change course over tens or hundreds of thousands of years, they can affect the evolution of birds and other species.
“The more we learn about Amazonian species, the more we realize how little is known,” Musher says. In the southern Amazon, including the region near the Roosevelt River, scientists continue to discover new species and genetically distinct populations of animals and plants.
Unfortunately, the southern Amazon Rainforest is also at the center of the region’s deforestation. As forest is slashed, burned and replaced for agricultural purposes, such as cattle and soy production, countless unique and spectacular species that occur there and nowhere else are becoming increasingly threatened by the prospect of extinction.
Understanding, appreciating and conserving biodiversity has been at the core of the Academy’s science work since its founding in 1812. With 19 million specimens and counting, our collections are not only a window into the past, but also a critical tool for measuring the current and future health of all Earth’s species.
During Biodiversity Year, join us as we bring our understanding of the natural world from the lab to City Hall and beyond, so that together, we are a force for nature.