How many species on Earth: one trillion! (Introduction)

by David Turell @, Wednesday, May 04, 2016, 00:01 (2886 days ago)

An enormous number based on new research:-https://www.sciencedaily.com/releases/2016/05/160502161058.htm-Earth could contain nearly 1 trillion species, with only one-thousandth of 1 percent now identified, according to a study from biologists at Indiana University.-***-"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 nonmicroscopic 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.-***-"Microbial species are all forms of life too small to be seen with the naked eye, including all single-celled organisms, such as bacteria and archaea, as well as certain fungi. Many earlier attempts to estimate the number of species on Earth simply ignored microorganisms or were informed by older datasets that were based on biased techniques or questionable extrapolations, Lennon said.-"'Older estimates were based on efforts that dramatically under-sampled the diversity of microorganisms," he added. "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."-"The realization that microorganisms were significantly under-sampled caused an explosion in new microbial sampling efforts over the past several years, including the collection of human-related microorganisms by the National Institutes of Health's Human Microbiome Project; marine microorganisms by the Tara Oceans Expedition; and aquatic, terrestrial and host-related microorganisms by the Earth Microbiome Project.-***-"'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.'"-Comment: It appears that micro-organismal biomass is bigger than ever. It obviously is much easier to modify (speciate) single-celled organisms than multicellular which adds many degrees of high complexity, the highly balanced function of organ systems to mention one aspect of it.

How many species on Earth: differentiation problem

by David Turell @, Wednesday, May 19, 2021, 18:31 (1044 days ago) @ David Turell

Sometimes organisms are so similar it is difficult to tell:

https://www.sciencedaily.com/releases/2021/05/210513142353.htm

"Evolutionary biologists have developed a new approach to genomic species delineation that improves upon current methods and could impact similar policy in the future.

"This approach is based on the fact that in many groups of organisms it can be problematic to decide where one species begins and another ends.

"'In the past, when it was challenging to distinguish species based on external characters, scientists relied on approaches that diagnosed signatures in the genome to identify 'breaks' or 'structure' in gene flow indicative of population separation. The problem is this method doesn't distinguish between two populations separated geographically versus two populations being two different species," said Jeet Sukumaran, computational evolutionary biologist at San Diego State University...

***

"In cases where it is difficult to sort the variation between individuals into differences due to variation within a species as opposed to between two species, they often turn to genomic data based approaches for the answer. This is when scientists often use a model that generates a population phylogeny, or an evolutionary tree relating different populations.

***

"Whether some of the population lineages in the sample are assigned to existing species or classified as entirely new species depends on two factors. One is the age of the population isolation events such as the splitting of an ancestral population into multiple daughter populations, which is how species are "born" in an extended process of speciation. The other is the rate of speciation completion, which is the rate at which the nascent or incipient species "born" from population splitting events develop into true full species.

"'We're coming to realize now that many organisms are cryptic species," Sukumaran said. "Many of them are similar looking even though they are actually distinct species separated by many tens or hundreds of thousands or even millions of years of evolution."

"This is either due to strong selection pressures to maintain the same morphology, or, more typically, due to very recent speciation resulting in insufficient time for external differences to develop.

***

"Currently, scientists apply a model based on multispecies coalescent theory to genomic data to identify the disruption of gene flow between different groups of organisms. This disruption is fundamental to species formation, but it can also occur between two different populations as well as two different species.

"While scientists agree that it is critical to distinguish between populations and species boundaries in genomic data, there is not always a lot of agreement on how to go about doing it. "If you ask ten biologists, you will get twelve different answers," Sukumaran said." (my bold)

Comment: We don't understand how speciation happens, and this problem of minor differences cannot be decided by splitter or lumper dispositions of researchers. Darwin's finches come to mind, all based on beak size.

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