Washington DC / Cambridge
(UK), 23 August 2011 - Eight million seven
hundred thousand (give or take 1.3 million)
is the latest estimated total number of
species on Earth and the most precise calculation
ever offered, according to a new study co-authored
by a researcher with the United Nations
Environment Programme (UNEP).
Around 6.5 million species
are found on land and 2.2 million (about
25 percent of the total) dwell in the ocean
depths. The report, which was co-authored
by Derek Tittensor at UNEP's World Conservation
Monitoring Centre (UNEP-WCMC), in Cambridge,
UK, also shows that 86% of all species on
land and 91% of those in the seas have yet
to be discovered, described or catalogued.
Announced today by Census
of Marine Life scientists and published
by PLoS Biology, the figure of 8.7 million
species is based on an innovative, validated
analytical technique that dramatically narrows
the range of previous estimates. Until now,
the number of species on Earth was said
to fall somewhere between 3 million and
100 million.
Says lead author Camilo
Mora of the University of Hawaii and Dalhousie
University in Halifax, Canada: "The
question of how many species exist has intrigued
scientists for centuries and the answer,
coupled with research by others into species'
distribution and abundance, is particularly
important now because a host of human activities
and influences are accelerating the rate
of extinctions. Many species may vanish
before we even know of their existence,
of their unique niche and function in ecosystems,
and of their potential contribution to improved
human wellbeing."
"This work deduces
the most basic number needed to describe
our living biosphere," says coauthor
Boris Worm of Dalhousie University. "If
we did not know - even by an order of magnitude
(1 million? 10 million? 100 million?) -
the number of people in a nation, how would
we plan for the future?"
"It is the same
with biodiversity. Humanity has committed
itself to saving species from extinction,
but until now we have had little real idea
of even how many there are."
Dr. Worm notes that
the recently-updated Red List issued by
the International Union for the Conservation
of Nature assessed 59,508 species, of which
19,625 are classified as threatened. This
means the IUCN Red List, the most sophisticated
ongoing study of its kind, monitors less
than 1% of world species.
The research is published
alongside a commentary by Lord Robert May
of Oxford, past president of the UK's Royal
Society, who praises the researchers' "imaginative
new approach."
"It is a remarkable
testament to humanity's narcissism that
we know the number of books in the US Library
of Congress on 1 February 2011 was 22,194,656,
but cannot tell you - to within an order-of-magnitude
- how many distinct species of plants and
animals we share our world with," Lord
May writes.
"(W)e increasingly
recognise that such knowledge is important
for full understanding of the ecological
and evolutionary processes which created,
and which are struggling to maintain, the
diverse biological riches we are heir to.
Such biodiversity is much more than beauty
and wonder, important though that is. It
also underpins ecosystem services that -
although not counted in conventional GDP
- humanity is dependent upon."
Drawing conclusions
from 253 years of taxonomy since Linnaeus
Swedish scientist Carl
Linnaeus created and published in 1758 the
system still used to formally name and describe
species. In the 253 years since, about 1.25
million species - roughly 1 million on land
and 250,000 in the oceans - have been described
and entered into central databases (roughly
700,000 more are thought to have been described
but have yet to reach the central databases).
To now, the best approximation
of Earth's species total was based on the
educated guesses and opinions of experts,
who variously pegged the figure in a range
from 3 to 100 million ? wildly differing
numbers questioned because there is no way
to validate them.
Drs. Mora and Worm,
together with Dalhousie colleagues Derek
P. Tittensor, Sina Adl and Alastair G.B.
Simpson, refined the estimated species total
to 8.7 million by identifying numerical
patterns within the taxonomic classification
system (which groups forms of life in a
pyramid-like hierarchy, ranked upwards from
species to genus, family, order, class,
phylum, kingdom and domain).
Analysing the taxonomic
clustering of the 1.2 million species today
in the Catalogue of Life and the World Register
of Marine Species, the researchers discovered
reliable numerical relationships between
the more complete higher taxonomic levels
and the species level.
Says Dr. Adl: "We
discovered that, using numbers from the
higher taxonomic groups, we can predict
the number of species. The approach accurately
predicted the number of species in several
well-studied groups such as mammals, fishes
and birds, providing confidence in the method."
When applied to all
five known eukaryote* kingdoms of life on
Earth, the approach predicted:
1) ~7.77 million species
of animals (of which 953,434 have been described
and cataloged)
2) ~298,000 species
of plants (of which 215,644 have been described
and cataloged)
3) ~611,000 species
of fungi (moulds, mushrooms) (of which 43,271
have been described and
cataloged)
4) ~36,400 species of
protozoa (single-cell organisms with animal-like
behavior, eg. movement,
of which 8,118 have
been described and cataloged)
5) ~27,500 species of
chromists (including, eg. brown algae, diatoms,
water moulds, of which 13,033 have been
described and cataloged)
Total: 8.74 million
eukaryote species on Earth.
(* Notes: Organisms
in the eukaryote domain have cells containing
complex structures enclosed within membranes.
The study looked only at forms of life accorded,
or potentially accorded, the status of "species"
by scientists. Not included: certain micro-organisms
and virus "types", for example,
which could be highly numerous.)
Within the 8.74 million
total is an estimated 2.2 million (plus
or minus 180,000) marine species of all
kinds, about 250,000 (11%) of which have
been described and catalogued. When it formally
concluded in October 2010, the Census of
Marine Life offered a conservative estimate
of 1 million+ species in the seas.
"Like astronomers,
marine scientists are using sophisticated
new tools and techniques to peer into places
never seen before," says Australian
Ian Poiner, Chair of the Census' Scientific
Steering Committee. "During the 10-year
Census, hundreds of marine explorers had
the unique human experience and privilege
of encountering and naming animals new to
science. We may clearly enjoy the Age of
Discovery for many years to come."
"The immense effort
entering all known species in taxonomic
databases such as the Catalogue of Life
and the World Register of Marine Species
makes our analysis possible," says
co-author Derek Tittensor, who also works
with Microsoft Research and the UN Environment
Programme's World Conservation Monitoring
Centre. "As these databases grow and
improve, our method can be refined and updated
to provide an even more precise estimate."
"We have only begun
to uncover the tremendous variety of life
around us," says co-author Alastair
Simpson. "The richest environments
for prospecting new species are thought
to be coral reefs, seafloor mud and moist
tropical soils. But smaller life forms are
not well known anywhere. Some unknown species
are living in our own backyards - literally."
"Awaiting our discovery
are a half million fungi and moulds whose
relatives gave humanity bread and cheese,"
says Jesse Ausubel, Vice-President of the
Alfred P. Sloan Foundation and cofounder
of the Census of Marine Life. "For
species discovery, the 21st century may
be a fungal century!"
Mr. Ausubel notes the
enigma of why so much diversity exists,
saying the answer may lie in the notions
that nature fills every niche, and that
rare species are poised to benefit from
a change of conditions.
In his analysis, Lord
May says the practical benefits of taxonomic
discovery are many, citing the development
in the 1970s of a new strain of rice based
on a cross between conventional species
and one discovered in the wild. The result:
30% more grain yield, followed by efforts
ever since to protect all wild varieties
of rice, "which obviously can only
be done if we have the appropriate taxonomic
knowledge."
"Given the looming
problems of feeding a still-growing world
population, the potential benefits of ramping
up such exploration are clear."
Based on current costs
and requirements, the study suggests that
describing all remaining species using traditional
approaches could require up to 1,200 years
of work by more than 300,000 taxonomists
at an approximate cost of $US 364 billion.
Fortunately, new techniques such as DNA
barcoding are radically reducing the cost
and time involved in new species identification.
Concludes Dr. Mora:
"With the clock of extinction now ticking
faster for many species, I believe speeding
the inventory of Earth's species merits
high scientific and societal priority. Renewed
interest in further exploration and taxonomy
could allow us to fully answer this most
basic question: What lives on Earth?"