Global biodiversity

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Examples of the biodiversity of the Earth.

The biodiversity of planet Earth is the total variability of life forms. Currently around 1.9 million extant species are believed to have been described,[1] but some scientists believe 20% are synonyms, reducing the total valid described species to 1.5 million. Scientists expect there to be 5 ± 3 million extant species on Earth.[2] Some 250,000 valid fossil species have also been named, but this is believed to be an even smaller 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.[3] However, the current rate and magnitude of extinctions are much higher than background estimates.[4] This, considered by some to be leading to the sixth mass extinction,[4] is a result of human impacts on the environment.[5]

Drivers that affect biodiversity[edit]

Measuring diversity[edit]

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

Taxonomic diversity, that is the number of species, genera, family is the most commonly assessed diversity type.[6] 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.[7]

Known species[edit]

Insects make up the vast majority of animal species.

Chapman, 2005 and 2009[1] 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perhaps the most comprehensive recent statistics on numbers of extant species, drawing on a range of published and unpublished sources, and has come up with a figure of approximately 1.9 million estimated described taxa, as against possibly a total of between 11 and 12 million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 [8] 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,[9][10][11] 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,[1] 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[edit]

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

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.[16] Given the 50,000 described tropical tree species, Erwin suggested that there are almost 10 million beetle species in the tropics.[17]

Global biodiversity indices[edit]

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.[18] 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.[19] 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.[20] 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[edit]

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.[21]

See also[edit]

References[edit]

  1. ^ a b c Chapman, A. D. (2009). Numbers of Living Species in Australia and the World (PDF) (2nd ed.). Canberra: Australian Biological Resources Study. pp. 1–80. ISBN 978 0 642 56861 8. 
  2. ^ Costello, Mark; Robert May; Nigel Stork (25 January 2013). "Can we name Earth's species before they go extinct?". Science 339. doi:10.1126/science.1230318. PMID 23349283. 
  3. ^ Sahney, S., Benton, M.J. & Falcon-Lang, H.J. (2010). "Rainforest collapse triggered Pennsylvanian tetrapod diversification in Euramerica" (PDF). Geology 38 (12): 1079–1082. doi:10.1130/G31182.1. 
  4. ^ a b Barnosky, A. D.; et al. (2011). "Has the Earth's sixth mass extinction already arrived?". Nature 471: 51–57. doi:10.1038/nature09678. 
  5. ^ a b Pereira, HM. "Global Biodiversity Change: The Bad, the Good, and the Unknown". Annual Review of Environment and Resources. 
  6. ^ Sahney, S. and Benton, M.J. (2008). "Recovery from the most profound mass extinction of all time" (PDF). Proceedings of the Royal Society: Biological 275 (1636): 759–65. doi:10.1098/rspb.2007.1370. PMC 2596898. PMID 18198148. 
  7. ^ Sahney, S., Benton, M.J. and Ferry, P.A. (2010). "Links between global taxonomic diversity, ecological diversity and the expansion of vertebrates on land" (PDF). Biology Letters 6 (4): 544–547. doi:10.1098/rsbl.2009.1024. PMC 2936204. PMID 20106856. 
  8. ^ Raup. D.M. (1986). "Biological extinction in earth history". Science 231: 1528–1533. doi:10.1126/science.11542058. 
  9. ^ IISE (2010). SOS 2009: State of Observed Species (PDF). Arizona State University: International Institute for Species Exploration. pp. 1–8. 
  10. ^ IISE (2011). SOS 2010: State of Observed Species (PDF). Arizona State University: International Institute for Species Exploration. pp. 1–10. 
  11. ^ IISE (2012). SOS 2011: State of Observed Species (PDF). Arizona State University: International Institute for Species Exploration. pp. 1–14. 
  12. ^ Encyclopedia Smithsonian: Numbers of Insects
  13. ^ Proceedings of the National Academy of Sciences, Census of Marine Life (CoML) BBC News
  14. ^ David L. Hawksworth, "The magnitude of fungal diversity: the 1•5 million species estimate revisited" Mycological Research (2001), 105: 1422-1432 Cambridge University Press Abstract
  15. ^ Acari at University of Michigan Museum of Zoology Web Page
  16. ^ Erwin, Terry L. (March 1982). "Tropical Forests: Their Richness in Coleoptera and Other Arthropod Species". In The Coleopterists Society. The Coleopterists Bulletin 36 (1): 74–75. ISSN 0010-065X. JSTOR 4007977. 
  17. ^ Pullin, Andrew (2002). Conservation Biology. Cambridge: Cambridge University Press. ISBN 9780521644822. Retrieved December 24, 2013. 
  18. ^ . Zoological Society of London http://www.zsl.org/science/research-projects/indicators-assessments/index,134,ZI.html.  Missing or empty |title= (help)
  19. ^ "Trends in the status of biodiversity". IUCN. Retrieved 25 November 2013. 
  20. ^ "Global Wild Bird Index". Biodiversity Indicators Partnership. 
  21. ^ De Groot, R.S.; et al. (2002). "A typology for the classification, and description and valuation of ecosystem functions, goods and services". Ecological Economics 41: 393–408. doi:10.1016/s0921-8009(02)00089-7. 

External links[edit]