What Drives the Rich Bird Biodiversity in the Tropics? Movement is Key

The Neotropics, a region rich in rainforests that stretches from Mexico to the southernmost tip of South America, is rich in bird biodiversity. Now, scientists have challenged a commonly held view that explains how so many species of birds came to inhabit this area, revealing a bit more about the movements of birds.

"The Neotropic zone has more species of birds than any other region on Earth," said Brian Smith, lead author of the new paper, in a news release. "The unanswered question has been-how did this extraordinary bird diversity originate?"

In the neotropics, bird speciation, which is the process by which new species are formed, is usually linked to changes in the Earth's landscape over time. For example, rivers change course and mountains rise, causing different climates that cause bird populations to divide and, over time, become different species. Yet in this case, the researchers present an alternative model: speciation in Neotropical birds can be explained by the movement of the animals across these geographical barriers rather than the changes in the landscape.

The scientists examined both of these two models, comparing genetic patterns among a diverse array of bird lineages that occur in the Neotropics. In all, the researchers looked at 27 lineages that contained populations situated on the opposite side of large dispersal barriers. With the genetic data, the scientists estimated the time that the populations became isolated from one another.

So what did they find? It turns out that most speciation occurred during the Pleistocene, which began around 2.6 million years ago, which is long after the origin of the Andes Mountains and Amazonian river system. This, in particular, seems to indicate that speciation occurred because the animals themselves moved, rather than because the geographic changed.

"It may be only in birds that the genetic sampling is sufficiently dense to examine how interactions between the landscape and natural populations of birds influence the speciation process," said Robb Brumfield, lead investigator, in a news release.

The findings are published in the journal Nature.