IL Y A PEUT - ÊTRE MILLE MILLIARDS DE FORMES DE VIE SUR LA TERRE, selon une étude publiée dans the Proceedings of the National Academy of Sciences (auteurs : J.T. Lennon & K.J. Locey, de l'Université d'Indiana).
Times of India, ce jour. Subodh Varma. Earth may be home to 1 trillion life forms.
Earth could contain nearly 1 trillion species, with only one-thousandth of 1 per cent now identified, according to a study from biologists at Indiana University.
The estimate, based on the intersection of large datasets and universal scaling laws, appears in the Proceedings of the National Academy of Sciences. The study's authors are Jay T Lennon and Kenneth J Locey of Indiana University, US.
The IU scientists combined microbial, plant and animal community datasets from government, academic and citizen science sources, resulting in the largest compilation of its kind. Altogether, these data represent over 5.6 million microscopic and non-microscopic species from 35,000 locations across all the world's oceans and continents, except Antarctica.
"Estimating the number of species on Earth is among the great challenges in biology," Lennon said. "Our study combines the largest available datasets with ecological models and new ecological rules for how biodiversity relates to abundance. This gave us a new and rigorous estimate for the number of microbial species on Earth.
"Until recently, we've lacked the tools to truly estimate the number of microbial species in the natural environment," he added. "The advent of new genetic sequencing technology provides an unprecedentedly large pool of new information."
"Older estimates were based on efforts that dramatically under-sampled the diversity of microorganisms," Lennon said. "Before high-throughput sequencing, scientists would characterize diversity based on 100 individuals, when we know that a gram of soil contains up to a billion organisms, and the total number on Earth is over 20 orders of magnitude greater."
"A massive amount of data has been collected from these new surveys," said Locey, whose work includes programming required to compile the inventory. "Yet few have actually tried to pull together all the data to test big questions.
"After analyzing a massive amount of data, we observed simple but powerful trends in how biodiversity changes across scales of abundance. One of these trends is among the most expansive patterns in biology, holding across all magnitudes of abundance in nature," he added.
Scaling laws, like those discovered by the IU scientists, are known to accurately predict species numbers for plant and animal communities. For example, the number of species scales with the area of a landscape.
"Until now, we haven't known whether aspects of biodiversity scale with something as simple as the abundance of organisms," Locey said. "As it turns out, the relationships are not only simple but powerful, resulting in the estimate of upwards of 1 trillion species."
The study's results also suggest that actually identifying every microbial species on Earth is an almost unimaginably huge challenge. To put the task in perspective, the Earth Microbiome Project - a global multidisciplinary project to identify microscope organisms - has so far cataloged less than 10 million species.
"Of those cataloged species, only about 10,000 have ever been grown in a lab, and fewer than 100,000 have classified sequences," Lennon said. "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."
