The Amazon rainforest is alive with seemingly endless plants, myriad birds and mammals, and more insects than you can count. Its biodiversity is legendary: though it only takes up 0.5% of the Earth’s land surface area, it contains 10% of all named species on the planet. Which begets the question: just how did such a variety of species come to be concentrated here? Scientists think that rivers are part of the answer—specifically, the changes of river systems over time.
Geological evidence suggests that the rivers of the Amazon are especially dynamic. It may take them only thousands or tens of thousands of years to change course, which are short periods of time for such a big change in a landscape. When rivers change course, they can spur the evolution of new species by separating populations of animals, leading to their genetic diversification. In the Amazon, you can see this by finding different species of birds and primates on opposite sides of a river.
To test the idea that changing river systems caused this differentiation, a team of scientists sequenced the genomes of six species of birds that live in the Amazon. Their analyses showed that the current arrangement of rivers in the area effectively separate populations of these six species, which can eventually lead to new species forming. That finding suggests that the movement of rivers is at least partly responsible for the Amazon’s incredible biodiversity.
Amazon appreciators and bird lovers have good reason to thank a river today.