Birds evolving ‘quickly’ in North America, study shows
But extinctions are rising faster, scientists warn
The rate at which new bird species appear is accelerating, especially in North and South America, according to an international study published Wednesday in the journal Nature.
But even at a rate of one new species every 700 years, diversification is massively outpaced by the number of extinctions caused by human influences, said Simon Fraser University biologist Arne Mooers, one of the lead authors. “Humans are often problematic for other forms of life.”
“Depending on the time frame you use —whether it’s 500 years or 10,000 years — the extinction rate is hundreds of times higher than the rate at which new species emerge,” he said. “This is a new thing, because clearly that rate is not sustainable over time.”
Mooers, post-doctoral fellow Jeff Joy and partners at the University of Sheffield, Yale and University of Tasmania used millions of years of DNA and fossil data to profile the world’s 9,993 bird species and to determine how fast new bird species are emerging.
Based on observations of other animals, they expected to see deceleration, which is a common feature in evolution. But that’s not what they got.
“We expected the rate to be decelerating, as ecological niches for new species fill up,” Mooers explained. “Early on, birds (acquired) feathered flight and started to do all the cool things that birds do and there were all these different ways to be a bird and so it was easy to make new species.”
But as more of the world is occupied with species, the ability of new species to arise and compete for resources diminishes. At least, it is supposed to diminish.
The researchers used DNA to determine when new species began to radiate from existing species from the age of dinosaurs.
“For any two species you can use DNA to determine when they last shared a common ancestor,” Mooers said. “So we can see when speciation is getting faster or slower through time and where that happens” through the fossil record.
Evolution appears to be slowing among birds in Australia, New Guinea and Africa and growing faster in the New World, he said.
Why the landscape in the Americas is so much more fertile for speciation isn’t exactly known.
Songbirds have a much longer history in Australia and Africa and those places could be reaching capacity a few million years earlier than the Americas.
Or, it could be that bird species near the equator are being packed into tighter spaces as the tropics have shrunk over the past 15 million years, effectively eliminating space and resources for new species to exploit.
“We have absolutely no idea,” Mooers said.
Mooers and his colleagues already have their computers chugging away on a massive set of data to begin to resolve some of those questions.