Global biodiversity

Examples of the multicellular 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 that ever lived on Earth are estimated to be extinct. Estimates on the number of Earth's current species range from 2 million to 1 trillion, of which about 1.74 million have been databased thus far and over 80 percent have not yet been described. More recently, in May 2016, scientists reported that 1 trillion species are estimated to be on Earth currently with only one-thousandth of one percent 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 extinct 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.

Drivers that affect biodiversity and help animals to resource energy

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.it helps animals to have energy

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 or species, ecological, morphological, and genetic diversity. Taxonomic diversity, that is the number of species, genera, family is the most commonly assessed type. A few studies have attempted to quantitatively clarify the relationship between different types of diversity. For example, the biologist Sarda Sahney 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, as of 2012. 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/Component group Described Global estimate (described + undescribed)
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
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
Notoptera 55
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


The distribution of numbers of known and undescribed (estimated) species on Earth, grouped by major taxonomic groups; according to Chapman 2009. Absolute number of species on the left (orange = estimated number of yet to be described species, blue = already described). Right: percentage of species already described (green) and estimated to be not yet known (yellow).

Estimates of total number of species

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. 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. A 2016 study concludes that Earth is home to 1 trillion species.

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.

Biodiversity loss

Summary of major biodiversity-related environmental-change categories expressed as a percentage of human-driven change (in red) relative to baseline (blue)

Biodiversity loss includes the worldwide extinction of different species, as well as the local reduction or loss of species in a certain habitat, resulting in a loss of biological diversity. The latter phenomenon can be temporary or permanent, depending on whether the environmental degradation that leads to the loss is reversible through ecological restoration/ecological resilience or effectively permanent (e.g. through land loss). The current global extinction (frequently called the sixth mass extinction or Anthropocene extinction), has resulted in a biodiversity crisis being driven by human activities which push beyond the planetary boundaries and so far has proven irreversible.

Even though permanent global species loss is a more dramatic and tragic phenomenon than regional changes in species composition, even minor changes from a healthy stable state can have dramatic influence on the food web and the food chain insofar as reductions in only one species can adversely affect the entire chain (coextinction), leading to an overall reduction in biodiversity, possible alternative stable states of an ecosystem notwithstanding. Ecological effects of biodiversity are usually counteracted by its loss. Reduced biodiversity in particular leads to reduced ecosystem services and eventually poses an immediate danger for food security, but also can have more lasting public health consequences for humans.

International environmental organizations have been campaigning to prevent biodiversity loss for decades, public health officials have integrated it into the One Health approach to public health practice, and increasingly preservation of biodiversity is part of international policy. For example, the UN Convention on Biological Diversity is focused on preventing biodiversity loss and proactive conservation of wild areas. The international commitment and goals for this work is currently embodied by Sustainable Development Goal 15 "Life on Land" and Sustainable Development Goal 14 "Life Below Water". However, the United Nations Environment Programme report on "Making Peace with Nature" released in 2020 found that most of these efforts had failed to meet their international goals.

See also


This page was last updated at 2022-11-18 15:26 UTC. Update now. View original page.

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