Global biodiversity

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Examples of the biodiversity of the Earth.

Global biodiversity is the measure of biodiversity on planet Earth and is defined as the total variability of life forms. More than 99 percent of all species, amounting to over five billion species, that ever lived on Earth are estimated to be extinct. Estimates on the number of Earth's current species range from 10 million to 14 million, of which about 1.2 million have been documented and over 86 percent have not yet been described. The total amount of DNA base pairs on Earth, as a possible approximation of global biodiversity, is estimated at 5.0 x 10³⁷, and weighs 50 billion tonnes. In comparison, the total mass of the biosphere has been estimated to be as much as 4 TtC (trillion tons of carbon).

In other related studies, around 1.9 million extant species are believed to have been described currently, but some scientists believe 20% are synonyms, reducing the total valid described species to 1.5 million. In 2013, a study published in Science estimated there to be 5 ± 3 million extant species on Earth. Another study, published in 2011 by PLoS Biology, estimated there to be 8.7 million ± 1.3 million eukaryotic species on Earth. Some 250,000 valid fossil species have been described, but this is believed to be a small proportion of all species that have ever lived.

Global biodiversity is affected by extinction and speciation. The background extinction rate varies among taxa but it is estimated that there is approximately one extinction per million species years. Mammal species, for example, typically persist for 1 million years. Biodiversity has grown and shrunk in earth's past due to (presumably) abiotic factors such as extinction events caused by geologically rapid changes in climate. Climate change 299 million years ago was one such event. A cooling and drying resulted in catastrophic rainforest collapse and subsequently a great loss of diversity, especially of amphibians. However, the current rate and magnitude of extinctions are much higher than background estimates. This, considered by some to be leading to the sixth mass extinction, is a result of human impacts on the environment.

Drivers that affect biodiversity

Habitat change (see: habitat fragmentation or habitat destruction) is the most important driver currently affecting biodiversity, as some 40% of forests and ice-free habitats have been converted to cropland or pasture. Other drivers are: overexploitation, pollution, invasive species, and climate change.

Measuring diversity

Biodiversity is usually plotted as the richness of a geographic area, with some reference to a temporal scale. Types of biodiversity include:

• taxonomic diversity
• species diversity
• ecological diversity
• morphological diversity
• genetic diversity

Taxonomic diversity, that is the number of species, genera, family is the most commonly assessed diversity type. A few studies have attempted to quantitatively clarify the relationship between different types of diversity. For example, Sarda Sahney a researcher at the University of Bristol has found a close link between vertebrate taxonomic and ecological diversity.

Known species

Insects make up the vast majority of animal species.

Chapman, 2005 and 2009 has attempted to compile perhaps the most comprehensive recent statistics on numbers of extant species, drawing on a range of published and unpublished sources, and has come up with a figure of approximately 1.9 million estimated described taxa, as against possibly a total of between 11 and 12 million anticipated species overall (described plus undescribed), though other reported values for the latter vary widely. It is important to note that in many cases, the values given for "Described" species are an estimate only (sometimes a mean of reported figures in the literature) since for many of the larger groups in particular, comprehensive lists of valid species names do not currently exist. For fossil species, exact or even approximate numbers are harder to find; Raup, 1986 includes data based on a compilation of 250,000 fossil species so the true number is undoubtedly somewhat higher than this. It should also be noted that the number of described species is increasing by around 18,000-19,000 extant, and approaching 2,000 fossil species each year at the present time, The number of published species names is higher than the number of described species, sometimes considerably so, on account of the publication, through time, of multiple names (synonyms) for the same accepted taxon in many cases.

Based on Chapman's (2009) report, the estimated numbers of described extant species as of 2009 can be broken down as follows:

Major group	Described	Global estimate (described + undescribed)	Component group	Described	Global estimate	Component group (2)	Described	Global estimate
Chordates	64,788	~80,500
			Mammals	5,487	~5,500
			Birds	9,990	>10,000
			Reptiles	8,734	~10,000
			Amphibia	6,515	~15,000
			Fishes	31,153	~40,000
			Agnatha	116	unknown
			Cephalochordata	33	unknown
			Tunicata	2,760	unknown
Invertebrates	~1,359,365	~6,755,830
			Hemichordata	108	~110
			Echinodermata	7,003	~14,000
			Insecta	~1,000,000 (965,431-1,015,897)	~5,000,000
						Archaeognatha	470
						Blattodea	3,684-4,000
						Coleoptera	360,000-~400,000	1,100,000
						Dermaptera	1,816
						Diptera	152,956	240,000
						Embioptera	200-300	2,000
						Ephemeroptera	2,500-<3,000
						Grylloblattaria	24
						Hemiptera	80,000-88,000
						Hymenoptera	115,000	>300,000
						Isoptera	2,600-2,800	4,000
						Lepidoptera	174,250	300,000-500,000
						Mantodea	2,200
						Mecoptera	481
						Megaloptera	250-300
						Neuroptera	~5,000
						Odonata	6,500
						Orthoptera	24,380
						Phasmatodea (Phasmida)	2,500-3,300
						Phthiraptera	>3,000-~3,200
						Plecoptera	2,274
						Psocoptera	3,200-~3,500
						Siphonaptera	2,525
						Strepsiptera	596
						Thysanoptera	~6,000
						Trichoptera	12,627
						Zoraptera	28
						Zygentoma (Thysanura)	370
			Arachnida	102,248	~600,000
			Pycnogonida	1,340	unknown
			Myriapoda	16,072	~90,000
			Crustacea	47,000	150,000
			Onychophora	165	~220
			non-Insect Hexapoda	9,048	52,000
			Mollusca	~85,000	~200,000
			Annelida	16,763	~30,000
			Nematoda	<25,000	~500,000
			Acanthocephala	1,150	~1,500
			Platyhelminthes	20,000	~80,000
			Cnidaria	9,795	unknown
			Porifera	~6,000	~18,000
			Other Invertebrates	12,673	~20,000
						Placozoa	1	-
						Monoblastozoa	1	-
						Mesozoa (Rhombozoa, Orthonectida)	106	-
						Ctenophora	166	200
						Nemertea (Nemertina)	1,200	5,000-10,000
						Rotifera	2,180	-
						Gastrotricha	400	-
						Kinorhyncha	130	-
						Nematomorpha	331	~2,000
						Entoprocta (Kamptozoa)	170	170
						Gnathostomulida	97	-
						Priapulida	16	-
						Loricifera	28	>100
						Cycliophora	1	-
						Sipuncula	144	-
						Echiura	176	-
						Tardigrada	1,045	-
						Phoronida	10	-
						Ectoprocta (Bryozoa)	5,700	~5,000
						Brachiopoda	550	-
						Pentastomida	100	-
						Chaetognatha	121	-
Plants sens. lat.	~310,129	~390,800
			Bryophyta	16,236	~22,750
						Liverworts	~5,000	~7,500
						Hornworts	236	~250
						Mosses	~11,000	~15,000
			Algae (Plant)	12,272	unknown
						Charophyta	2,125	-
						Chlorophyta	4,045	-
						Glaucophyta	5	-
						Rhodophyta	6,097	-
			Vascular Plants	281,621	~368,050
						Ferns and allies	~12,000	~15,000
						Gymnosperms	~1,021	~1,050
						Magnoliophyta	~268,600	~352,000
Fungi	98,998 (incl. Lichens 17,000)	1,500,000 (incl. Lichens ~25,000)
Others	~66,307	~2,600,500
			Chromista [incl. brown algae, diatoms and other groups]	25,044	~200,500
			Protoctista [i.e. residual protist groups]	~28,871	>1,000,000
			Prokaryota [ Bacteria and Archaea, excl. Cyanophyta]	7,643	~1,000,000
			Cyanophyta	2,664	unknown
			Viruses	2,085	400,000
Total (2009 data)	1,899,587	~11,327,630

Estimates of total number of species

However the total number of species for some taxa may be much higher.

• 10-30 million insects;
• 5-10 million bacteria;
• 1.5 million fungi;
• ~1 million mites

In 1982, Terry Erwin published an estimate of global species richness of 30 million, by extrapolating from the numbers of beetles found in a species of tropical tree. In one species of tree, Erwin identified 1200 beetle species, of which he estimated 163 were found only in that type of tree. Given the 50,000 described tropical tree species, Erwin suggested that there are almost 10 million beetle species in the tropics. In 2011 a study published in PLoS Biology estimated there to be 8.7 million ± 1.3 million eukaryotic species on Earth.

Global biodiversity indices

After the Convention on Biological Diversity was signed in 1992, biological conservation became a priority for the international community. There are several indicators used that describe trends in global biodiversity. However, there is no single indicator for all extant species as not all have been described and measured over time. There are different ways to measure changes in biodiversity. The Living Planet Index (LPI) is a population-based indicator that combines data from individual populations of many vertebrate species to create a single index. The Global LPI for 2012 decreased by 28%. There are also indices that separate temperate and tropical species for marine and terrestrial species. The Red List Index is based on the IUCN Red List of Threatened Species and measures changes in conservation status over time and currently includes taxa that have been completely categorized: mammals, birds, amphibians and corals. The Global Wild Bird Index is another indicator that shows trends in population of wild bird groups on a regional scale from data collected in formal surveys. Challenges to these indices due to data availability are taxonomic gaps and the length of time of each index. The Biodiversity Indicators Partnership was established in 2006 to assist biodiversity indicator development, advancement and to increase the availability of indicators.

Importance of biodiversity

Biodiversity is important for humans through ecosystem services and goods. Ecosystem services are broken down into: regulating services such as air and water purification, provisioning services (goods), such as fuel and food, cultural services and supporting services such as pollination and nutrient cycling.

See also

• 2010 Biodiversity Indicators Partnership
• Extinction event
• Global Species Database
• Conservation

External links

• Biodiversity A-Z
• Wikispecies
• Biodiversity—Global issues