From the window from a passenger plane flying over the Amazon, the view is breathtaking. “It’s just a few miles from rivers and river islands,” said Lukas Musher, a postdoctoral researcher at Drexel University’s Academy of Natural Sciences.
The massive rivers below branch out into a dense, wooded network that has been continually rearranged for hundreds of thousands of years, drawing new paths and erasing old ones. Rivers divide and subdivide the forest into spaces that are each a whole world for the countless creatures that sway, crawl, and fly within their ever-changing boundaries.
In a new study in the journal Advances in Science, Musher and co-authors report that the endless remodeling of rivers increases the biodiversity of the beautiful birds that color the dense Amazon rainforests. Acting as a “species bomb,” dynamic rivers could be playing a more important role than previously realized in transforming the Amazon rainforest into one of the most biodiverse places on the planet. Although the lowlands of the forest represent only half a percent of the planet’s land surface, they are home to about 10 percent of all known and certainly many unknown species.
The idea that changing rivers can shape bird speculation dates back to the 1960s, but most researchers have ignored the phenomenon as an engine of much diversification for birds or mammals. “For a long time we thought the rivers were a bit static,” said John Bates, curator of the Field Museum in Chicago, who did not participate in the study.
But recently, biologists have begun to pay attention to the growing whispers of geologists. “One of the things that most provoked reflection for biologists was realizing the dynamics that geologists began to think were rivers,” Bates said. He said that the way this article combines biological data with geological ideas is very orderly.
The relationship between geographic change and biodiversity is “one of the most controversial topics in evolutionary biology,” said Musher, who did the study as part of his doctoral dissertation. Some researchers say Earth’s history has little influence on biodiversity patterns, but others suggest an “extremely close, basically linear” relationship between the two, Musher said.
Movement in time
To understand how river rearrangements might be shaping birds in the Amazon, Musher and his collaborators at the American Museum of Natural History and Louisiana State University made an expedition to the rivers that run through the heart of Brazil on June 2018.
They collected examples of multi-point birds on both sides of the river: the Aripuanã River and the Roosevelt River, named after Teddy Roosevelt, who traveled there in 1914 as part of a cartography team. . They also borrowed samples previously collected near other Amazon rivers by other institutions.
River rearrangements greatly affect the evolution of the groups of birds studied, including members of the Hypocnemis (left) and the Malacoptila (right) genres.Photography: (Left) Hector Bottai; (Right) Gonzo Lubitsch
