From the window of a passenger plane flying over the Amazon, the views are breathtaking. “It’s only miles across river and river islands,” said Lukas Musher, a postdoc researcher at Drexel University’s Academy of Natural Sciences.
The massive rivers below branch out into a dense, tree-like network that has continuously rearranged itself through hundreds of thousands of years, drawing new paths and erasing old ones. The rivers divide and subdivide the forest into spaces, each of which is a whole world of the innumerable creatures that swing, crawl, and fly within their ever-changing boundaries.
IN a new study in the journal The progress of science, Musher and his co-authors report that the endless relocation of rivers is increasing the biodiversity of the beautiful birds that color the dense rainforests of the Amazon. By acting as a “species pump”, the dynamic rivers can play a greater role than previously realized in shaping the Amazon forest into one of the most biodiverse locations on the planet. Although the lowlands of the forest make up only half a percent of the planet’s land area, they house about 10 percent of all known species – and no doubt many unknown ones.
The idea that changing rivers can shape bird species dates from the 1960s, but most researchers have disregarded the phenomenon as a driving force for much diversification for birds or mammals. “For a long time, we’ve really considered the rivers a kind of static,” he said John Batesa curator at the Field Museum in Chicago who was not involved in the investigation.
But recently, biologists began to pay attention to the louder and louder whispers from geologists. “One of the most thought-provoking things for biologists was realizing how dynamic geologists began to believe the rivers were,” Bates said. The way this paper weaves biological data along with geological ideas is very neat, he said.
The relationship between geographic change and biodiversity is “one of the most controversial topics in evolutionary biology,” said Musher, who conducted the study as part of his doctoral dissertation. Some scientists say Earth’s history has little bearing on the patterns of biodiversity, but others suggest “an extremely tight, fundamentally linear” relationship between the two, Musher said.
Movement over time
To understand how river diversions can shape birds in the Amazon, Musher and his collaborators from the American Museum of Natural History and Louisiana State University conducted an expedition to the rivers that run through the heart of Brazil in June 2018.
They collected examples of birds from several locations on either side of two rivers: the Aripuanã River and the Roosevelt River, named after Teddy Roosevelt, who traveled there in 1914 as part of a mapping team. They also borrowed samples previously collected near other rivers in the Amazon by other institutions.