Wednesday, December 14, 2016

The number of species of birds and what it says about the number of species of reptiles

This blog usually focuses on non-avian reptiles. However, the research reported here on birds has great implications for how we think about the number of species of reptiles. Birds are the most studied group of vertebrates, reptiles are much less studied. Thus if it is possible to double the number of bird species, the number of reptile species is much, much greater than any of the current estimates.

According the the Reptile Database between February 2008 and August 2016, the number of reptiles increased from 8734 to 10,450, in increase of 1716 species or 19.6%.  Just considering the years between 2010 and 2016 there have been 972 new species of reptiles described. While during that same period (2010 to 2016) only 51 species of birds were described. Thus it would seem that the number of species of reptiles particularly squamates (lizards and snakes) is dramatically higher than my estimate made in my 2011 post.

In time of climate change, habitat destruction, pollution, and other forms of environmental degradation are occurring more rapidly than in previous history - it is entirely possible that many species are becoming extinct before they have been described.
The above map was published in 2012 by Saving Species.The variety of life on Earth is not spread evenly, but is concentrated in very special places. Above the world map is color coded for density of vertebrate species. Colors indicate the highest concentrations of the number of animal species across the world's land masses. Deep reds and yellows cover much of the tropics, indicating a huge number of species. The world’s high latitudes and its deserts are blue, indicating relatively low vertebrate diversity. 
New research led by the American Museum of Natural History suggests that there are about 18,000 bird species in the world -- nearly twice as many as previously thought. The work focuses on "hidden" avian diversity -- birds that look similar to one another, or were thought to interbreed, but are actually different species. Recently published in the journal PLOS ONE, the study has serious implications for conservation practices.

"We are proposing a major change to how we count diversity," said Joel Cracraft, an author of the study and a curator in the American Museum of Natural History's Department of Ornithology. "This new number says that we haven't been counting and conserving species in the ways we want."

Birds are traditionally thought of as a well-studied group, with more than 95 percent of their global species diversity estimated to have been described. Most checklists used by bird watchers as well as by scientists say that there are roughly between 9,000 and 10,000 species of birds. But those numbers are based on what's known as the "biological species concept," which defines species in terms of what animals can breed together.

"It's really an outdated point of view, and it's a concept that is hardly used in taxonomy outside of birds," said lead author George Barrowclough, an associate curator in the Museum's Department of Ornithology.

For the new work, Cracraft, Barrowclough, and their colleagues at the University of Nebraska, Lincoln, and the University of Washington examined a random sample of 200 bird species through the lens of morphology -- the study of the physical characteristics like plumage pattern and color, which can be used to highlight birds with separate evolutionary histories. This method turned up, on average, nearly two different species for each of the 200 birds studied. This suggests that bird biodiversity is severely underestimated, and is likely closer to 18,000 species worldwide.

The researchers also surveyed existing genetic studies of birds, which revealed that there could be upwards of 20,000 species. But because the birds in this body of work were not selected randomly -- and, in fact, many were likely chosen for study because they were already thought to have interesting genetic variation -- this could be an overestimate. The authors argue that future taxonomy efforts in ornithology should be based on both methods.

"It was not our intent to propose new names for each of the more than 600 new species we identified in the research sample," Cracraft said. "However, our study provides a glimpse of what a future taxonomy should encompass."

Increasing the number of species has implications for preserving biodiversity and other conservation efforts.

"We have decided societally that the target for conservation is the species," said Robert Zink, a co-author of the study and a biologist at the University of Nebraska, Lincoln. "So it follows then that we really need to be clear about what a species is, how many there are, and where they're found."

Barrowclough GF, Cracraft J, Klicka J, Zink RM. 2016 How Many Kinds of Birds Are There and Why Does It Matter? PLOS ONE, 2016; 11 (11): e0166307 DOI: 10.1371/journal.pone.0166307

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