from the window A passenger plane flies over the Amazon River and the view is breathtaking. “It’s just miles away from rivers and river islands,” said Lukas Musher, a postdoctoral researcher in Drexel University’s School of Natural Sciences.
The vast river below branches into a dense tree-like network that has been continuously rearranged over hundreds of thousands of years, making new paths and erasing old ones. The river divides and subdivides the forest into spaces, each of which is a complete world for countless creatures to swing, crawl and fly within its ever-changing boundaries.
exist a new study in the magazine scientific progress, Musher and his co-authors report that the endless reshuffling of rivers increases the biodiversity of beautiful birds in the Amazon’s lush rainforest. By acting as “species pumps,” vibrant rivers may play a greater role than previously realized in shaping the Amazon forest into one of the most biodiverse places on Earth. Although the lowlands of forests cover only 0.5 percent of the Earth’s land area, they are home to about 10 percent of known species—and no doubt many unknowns.
The idea that river flows can shape bird species dating back to the 1960s, but most researchers have ignored this phenomenon as a driver of bird or mammal diversification. “For a long time, we really thought the river was still,” says John BatesCurator at the Field Museum in Chicago, who was not involved in the study.
But recently, biologists have begun to pay attention to the increasingly loud whispers of geologists. “One of the most thought-provoking things for biologists is realizing how active geologists are starting to think rivers are,” Bates said. The way the paper combines biological data with geological ideas is ingenious, he said.
The relationship between geographic change and biodiversity is “one of the most controversial topics in evolutionary biology,” said Musher, who conducted the research as part of his doctoral work. Some researchers say Earth’s history has little effect on patterns of biodiversity, but others see an “extremely tight, largely linear” relationship between the two, Musher said.
movement across time
To understand how river rearrangement might shape birds in the Amazon, Musher and his collaborators from the American Museum of Natural History and Louisiana State University surveyed rivers flowing through central Brazil in June 2018.
They collected examples of birds from multiple locations on either side of two rivers: the Aripuanã and Roosevelt rivers, named after Teddy Roosevelt, who traveled there in 1914 as part of a surveying team. They also borrowed samples previously collected by other agencies near other rivers in the Amazon.
River rearrangement greatly affects evolution of studied bird populations, including members of birds gastrocnemius (left) and Malakotila (right) Genus.Photos: (left) Hector Bottai; (right) Gonzo Lubitsch
