November 1, 2012
Scientists Work On Completing The Avian Family Tree
April Flowers for redOrbit.com - Your Universe Online
A new study, led by Yale University, has created the most comprehensive family tree for birds to date. It connects all living bird species — nearly 10,000 — and reveals some surprising new details about the evolutionary history and geographic context of the birds.
By analyzing the family tree, the research team was able to show when and where birds diversified. They also found that the birds' diversification rate has increased over the last 50 million years, which challenges the conventional wisdom of biodiversity experts.
"It's the first time that we have – for such a large group of species and with such a high degree of confidence – the full global picture of diversification in time and space," said biologist Walter Jetz of Yale. The findings of the new study are were published online in the journal Nature.
"The research highlights how heterogeneously fast diversifying species groups are distributed throughout the family tree and over geographic space. Many parts of the globe have seen a variety of species groups diversify rapidly and recently. All this leads to a diversification rate in birds that has been increasing over the past 50 million years," Jetz continued.
The research team, which included members from the University of Bristol, Simon Fraser University and the University of Tasmania, relied heavily on fossil and DNA data, which they combined with geographical information to produce the family tree.
"The current zeitgeist in biodiversity science is that the world can fill up quickly," says biologist and co-author Arne Mooers of Simon Fraser University in Canada. "A new distinctive group, like bumblebees or tunafish, first evolves, and, if conditions are right, it quickly radiates to produce a large number of species. These species fill up all the available niches, and then there is nowhere to go. Extinction catches up, and things begin to slow down or stall. For birds the pattern is the opposite: Speciation is actually speeding up, not slowing down."
The growing rate of avian diversity can be attributed to an abundance of group-specific adaptations. The team hypothesizes that repeated bursts of diversification were enabled by the evolution of physical or behavioral innovations in certain groups combined with the opening of new habitats. Birds' exceptional mobility, which has allowed them to colonize new regions and exploit novel ecological opportunities over and over again is another likely factor.
The researchers expose significant geographic differences in diversification rates; they are higher in the Western Hemisphere than in the Eastern. They are also higher on islands than mainlands. The team was surprised to find there is little difference in rates between the tropics and high latitudes. The study found that regions of especially intense recent diversification include northern North America and Eurasia and southern South America.
"This was one of the big surprises," Jetz said. "For a long time biologists have thought that the vast diversity of tropical species must at least partly be due to greater rates of net species production there. For birds we find no support for this, and groups with fast and slow diversification appear to occur there as much as in the high latitudes. Instead, the answer may lie in the tropics' older age, leading to a greater accumulation of species over time. Global phylogenies like ours will allow further tests of this and other basic hypotheses about life on Earth."