Earth home to a trillion species


A new study relying on the most comprehensive datasets yet suggests there may be much more diversity than previously thought. Phil Ritchie reports.


Strands of the Streptomyces coelicoflavus soil bacteria and chains of round Streptococcus bacteria in a soil sample. New techniques have hown many more organisms than previously thought. – Science Photo Library/Getty Images

A new study has dramatically increased estimates of the number of species of life on Earth to one trillion – and we have discovered less than 1% of them.

The study by two biologists from the US's Indiana University, Kenneth Locey and Jay Lennon, was the largest of its kind ever undertaken. It combined the largest available datasets with ecological models and new ecological rules for how biodiversity relates to overall numbers of organisms.

The scientists looked at every continent except Antarctica with data representing 5.6 million species from 35,000 locations.

These numbers were then tested using a “scaling law”, which quantifies the number of species in a small area and extrapolates the results to cover larger masses of land.

This allows the presence of unidentified species to be included in the total.

"This gave us a new and rigorous estimate for the number of microbial species on Earth," Lennon says.

The team put the huge increase in the estimated total number of species down to new discoveries of the vast diversity of microbes such as bacteria and other single-celled organisms.

"Until recently, we’ve lacked the tools to truly estimate the number of microbial species in the natural environment," Lennon says.

"Older estimates were based on efforts that dramatically under-sampled the diversity of microorganisms."

Previous calculations of micro­-organism numbers depended almost entirely on the ability to culture bacteria in the lab.

But advances in DNA sequencing now show that a gram of soil contains up to a billion organisms, forcing a rethink in the overall species numbers.

Of the 10 million catalogued species, only about 10,000 have ever been grown in a lab, says Lennon: “And fewer than 100,000 have classified sequences. Our results show that this leaves 100,000 times more microorganisms awaiting discovery – and 100 million to be fully explored.

“Microbial biodiversity, it appears, is greater than ever imagined.”

The research was published in the Proceedings of the National Academy of Sciences.

  1. http://www.pnas.org/content/early/2016/04/26/1521291113.abstract?sid=c39e1e9e-f2f1-4a70-8d0e-d6086a9be675
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