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Example of great biodiversity: Up to 80 different epiphytes can be found on a tree in the cloud forest of the Andes .
Mixed forest on the Rivière Saguenay in Canada

Species diversity - also called species diversity - describes the number of biological species within a certain habitat ( biotope , biome or ecoregion ) or a geographically limited area (e.g. mountains, land, grid cell ) in biology . It is often differentiated according to flora or fauna or, more specifically, according to traditional biological classes(e.g. biodiversity of plants, trees, insects, fish, amphibians, reptiles, birds, mammals, etc.). The diversity of species is part of biodiversity and the most important measure for its characterization.

Species, biological diversity, biodiversity

"Species diversity" is part of biodiversity or "biological diversity". In addition to the diversity of species, this also includes genetic diversity and the diversity of ecosystems . Species diversity is often used synonymously with biodiversity ; Species diversity is the clearest form of biodiversity.

International days of action or remembrance

Since 2000, the calls UNESCO annual "International Day for Biological Diversity" (International Day for Biological Diversity) on, initially for 29 December, the day on which the Convention on Biological Diversity ( Convention on Biological Diversity) 1993 into force internationally entered, since 2001 for May 22nd, the day on which the UN Convention on Biodiversity was adopted on May 22nd, 1992 in Nairobi . In 2020, the international motto was “Our solutions are in nature”, and in German “Our biodiversity, our nutrition, our health”, indicating a direct connection between the preservation of biodiversity and human beings Diet and health should be noted. In 2021, it was proclaimed a virtual Global Biodiversity Festival , with a 72-hour program highlighting the ongoing global extinction of species.

Since 1999, the German-language magazine GEO has also celebrated a “Nature Day” annually for June, and in the German-speaking area it is again “International Day of Biodiversity” or “International Day of Biodiversity”. In addition, there are activities of various organizations that regularly remind of biodiversity or actively call for the local biodiversity to be recorded, including about the hour of the garden birds of the German Nature Conservation Union (NABU).

Described species

Global distribution of vascular plant species , number of species per 10,000 km² <100 100–200 200–500 500–1,000 1,000–1,500 1,500–2,000 2,000–3,000 3,000–4,000 4,000–5,000 > 5,000

In the Global Biodiversity Assessment, prepared on behalf of UNEP ( United Nations Environment Program ) in 1995, a total of around 1.75 million described species was given for the earth. This number is only an estimate. An exact list does not exist. Today one reckons with a total of over 2 million described species. It is difficult to give the exact number of species described, because

  • many species have been described several times and the scientific synonyms are only eliminated in the course of time and
  • Many supposedly uniform taxa are divided into several species by molecular genetic engineering, but often have not yet been given a name (so-called cryptic species ). In the case of the prokaryotes, all modern species concepts, and thus also the very high number of species mentioned recently, are based on forms that can only be distinguished by genetic analysis. The extent to which taxa, which can be distinguished by molecular genetics but are morphologically identical, are accepted as species for animal and plant species depends heavily on the respective scientific species concept.

Taxonomists therefore often differentiate between “nominal species” (number of names) and “valid species” (number of real units). More than 50,000 nominal species of fish have currently been described; Of these, around 31,000 valid species are currently accepted (as of 2009). Most of the synonyms go back to the early pioneering days of taxonomy. Of the species newly described since around 1970, only a tiny fraction turned out to be synonymous.

Currently around 260,000 vascular plant species (possibly also 400,000: Govaerts 2001,) around 50,000 vertebrate species and around 1 million insect species have been described (estimates: Nielsen & Mound: 865,000 species). Since vascular plants have a comparatively large number of species and are much easier to record than insects, for example, and because the global distribution of these plants largely corresponds to that of other taxa, their biodiversity is often used for mapping global biodiversity (see world map) .

Between 240,000 and 330,000 species are known from the seas (estimates: 242,000 species in the Global Biodiversity Assessment, 230,000 species according to Bouchet, 318,000 species according to Reaka-Kudla). About 51 percent of all species described today are insects and about 14 percent belong to the vascular plants. The rest of around 35 percent (around 700,000 species) are made up of the other animal and plant organisms, including all unicellular organisms and all vertebrates.

Currently 4,500 prokaryote species (bacteria and archaebacteria) have been described, which means that they have been given a scientific name according to the nomenclature rules. For many microbiologists, however, it seems questionable whether the species definition derived from the description of plant and animal species is applicable to prokaryotes (see physiological species concept for bacteria ). According to the phylogenetic species concept, there are no types of bacteria ( Ernst Mayr ).

The number of species can also be broken down by habitat : of the currently described two million species, around 78 percent live on the mainland , 17 percent in water and around 5 percent (around 100,000 species) live as parasites or symbionts in other organisms (the latter number depends heavily on the definition of parasitism and symbiosis ). The Census of Marine Life project has yielded important new findings on the biodiversity of the oceans .

Estimates of the total number of species on earth

Distribution of the described and recognized species to the groups of organisms according to estimates from the 1990s

The global total number of all species was estimated in the past two decades very differently between 3.6 million and 112 million . The estimates were extrapolated on the basis of the approximately 1.75 million species described in the mid-1990s. The Global Biodiversity Assessment of 1995, for which more recent estimates have been developed for many subgroups in recent years, provides a differentiated overview of the estimate at that time. A more up-to-date overview was no longer drawn up.

Some widely cited estimates:

  • In 1982 Terry L. Erwin published a study of beetle species that he found on a tropical tree species ( Luehea seemannii ) in Panama. He found a total of around 1,200 beetle species, of which he estimated 163 to be host-specific (i.e. they are said to only live on L. seemannii ). By extrapolating to the (estimated) 50,000 tropical tree species and the proportion of beetles in the total fauna, he extrapolated a total of 30 million arthropod species in the tropical tree canopy. Erwin's work has been criticized many times. Many peers are of the opinion that he has overestimated the proportion of specialized species. With the same approach, they come up with 5 to 7 million species.
  • Grassle and Maciolek extrapolated from the number of bottom-living species from samples obtained with a gripper from the deep-sea floor to the total number of species for bottom-living macroorganisms (e.g. mollusks, polychaetes, crustaceans) on the sea floor. They came in 10 million ways. Their approach has also been criticized many times as being excessive.
  • In 1991 Hawksworth estimated the worldwide number of mushroom species by extrapolating the (very well researched) British numbers to the (mostly poorly researched) rest of the world and came to about 1.5 million mushroom species. Hawksworth and Lücking publish new results in 2017. In 2017 they estimated the global number at 2.2 to 3.8 million mushroom species. In 2017, however, only around 120,000 mushroom species were actually described worldwide.
  • Stork and Gaston tried to extrapolate the number of insect species from the relatively well-researched number of butterflies (butterflies). There are 67 butterfly species and 22,000 other insect species in England. With 15,000 to 20,000 butterflies worldwide, there would be a total of 4.9 to 6.6 million insect species.
  • Numerous researchers, among them z. B. May, draw attention to the largely unknown, but probably very high number of parasitic species. If every wild animal species were to harbor a specific parasitic protozoa and a nematode, the number of species identified otherwise would have to be tripled.
  • According to a 2011 study, there are 8.7 million species of organisms on earth. 6.5 million of them live on land and 2.2 million in the oceans. These numbers come from the "Census of Marine Life", whose scientists have succeeded in making the most accurate estimate of the number of species ever made with the help of a new method of family tree analysis.

The number of species actually living on earth is, by all serious estimates, far higher than the number currently described. Almost all researchers agree, however, that useful numerical values ​​can hardly be given at the moment. All estimates are extremely dependent on the estimates for the tropical rainforests, for which far too few reliable data are available. Gaston and May point out, for example, that in all of the “developing countries” on earth, only about 6% of taxonomists work. At the same time, the positions for taxonomists are also being deleted in the rich nations, so that, only half ironically, some have proclaimed the taxonomist himself an endangered species. In addition, well-intentioned regulations on the property rights to species as a result of the Convention on Biological Diversity hinder research because some states also regard previously unknown species as their property and hinder research. For some animal groups there are serious indications that some estimated values ​​could possibly be far exaggerated. Lambshead and Boucher suspect, for example, that the number of marine nematodes, which at times has been estimated to be over 10 million species (there are even isolated figures of 100 million), is much lower (less than a million, possibly significantly less). In fact, 26,646 species have been described (in 2001).

The next largest groups presumed after insects in terms of species numbers are fungi , algae and perhaps nematodes and arachnids . The vertebrates do not matter at all in the total number of species. The total number of species of mammals is estimated at around 4,000, and that of birds at 8,500 to 9,500. Around 3 bird species are described anew each year. Although large mammal species are still occasionally described today (for example a whale species in 1991 and a large mammal in 1993 with the Vu Quang cattle ), significant new discoveries are hardly to be expected here.

Today it is more likely that the total number of species on earth is around 5 (up to perhaps 20) million species. Among the most renowned specialists in the field, Nigel Stork has put forward an estimate of 5 to 15 million. Robert May estimates - with many reservations - it is possibly up to 20 million. A central database for all systematized species does not yet exist. The total number also depends very much on what is viewed as a species in the respective groups of organisms and depends on the respective species concept. Around 12,000 to 25,000 species are newly described each year (the long-term average is just over 13,000), and many of them later often turn out to be synonyms for species already described. In this respect, a distinction is made between so-called “nominal species” and “valid species”. The latter are the "good species" accepted in each case after a critical review by appropriate specialists. Today, species separation is often carried out by means of molecular genetic investigations or at least supplemented by them.

The number of "species" in prokaryotes is a problem of its own. The usual microbiological methods are worthless here, since, according to approximate investigations, less than 1% of the bacterial species found in natural samples (according to the genome) could be cultivated and multiplied in the usual nutrient media. Through a species definition that defines strains with a genetic similarity (according to the degree of recombination) of less than 70% as species, and extrapolations from soil samples analogous to the examples above, Dykhuizen found a billion bacterial species in 2005. Perhaps this number should be understood as the extent of our ignorance.

Biodiversity in different countries


4,105 higher plant species ( vascular plants ) are known from the territory of the Federal Republic of Germany . According to an estimate by Völkl and Blick 2004, 44,787 multicellular animal species are documented. Of these, 38,370 are arthropod species , of which the insects make up the largest part with 33,305 species. A total of only 706 vertebrate species have been recorded in Germany. In an international comparison, the flora and fauna of Germany are very well known. Nevertheless, new species are still found or even described anew every year in Germany.

However, the biodiversity in Germany is increasing particularly in the arable regions such as B. Northwest Germany in the course of the intensification of agriculture sharply. This is particularly evident in the field birds such as partridge , skylark and bunting . Researchers from the Zoological State Collection in Munich found 2.6 times the amount of biomass on organically farmed agricultural land compared to conventionally farmed land .


The total number of species in Switzerland was estimated at around 60,000 in 2011. An investigation in the Basel Zoo revealed over 3,100 directly identifiable species on its premises, with the non-directly identifiable species being estimated at 5,500 there. However, despite the efforts of the last few decades, biodiversity in Switzerland is declining. The protective measures were unable to keep pace with the persistent or even increasing threats.

Species threat and extinction

According to the International Union for Conservation of Nature and Natural Resources ( IUCN ), around 12% of the species of birds , 20% of mammals , 29% of amphibians and 33% of the naked plant species were considered threatened in 2007 . These four groups are also the only ones whose threat status is based on an evaluation of all or at least most of the species. Only a relatively small percentage of the other groups (e.g. fish , insects , mosquitoes ) have been evaluated worldwide, so that the threat figures found cannot be statistically extrapolated to the group as a whole. For example, only 1255 relatively conspicuous insect species out of a total of around 1 million described (and numerous undescribed) insect species have been checked, so that no realistic statement can be made about the threat status of the insects as a whole.

The “Living Planet Index” of the WorldWildlifeFund ( WWF ) stated in 2014 that the diversity of species on earth fell by 52 percent between 1970 and 2010. Latin America suffers the greatest loss with an average of 83 percent. The populations of species living on land fell by 39 percent, freshwater species by 76 percent, and marine species by 39 percent.

The current extinction of species is often compared with the great mass extinctions of the past. During the past 600 million years, paleontologists traditionally differentiate between five (sometimes more) major species extinctions, which, according to more recent findings, proceeded very quickly according to geological standards and sometimes occurred within a few 10,000 years. These biological crises were sometimes flanked before and after by smaller extinction events and only represent the most noticeable deviations of the constantly fluctuating number of species. One difficulty in the analysis is that the respective fossil site is not a 1: 1 image of the former biodiversity and species extinction but only provides information about the former species that can be fossilized under the respective conditions. Other problems that make a comparison with the current situation difficult are e.g. B. the fossil remains with few features, which often do not make it possible to really define individual species in a biological sense; often the descriptions correspond to whole genres or even higher systematic units. The most significant difference between earlier mass extinctions and the current situation is that today's extinction is caused by a single biological species, namely humans with their activities and their space and resource requirements, while earlier causes were probably mainly geological or atmospheric-cosmic causes.

Causes of the extinction of species today

In 2019, the Intergovernmental Platform on Biodiversity and Ecosystem Services (IPBES) published a report on global biodiversity, highlighting the current mass extinction .

"The fact that the value of ecosystems and biodiversity has so far not been economically recognized is a decisive cause of the alarming destruction of nature."

- Pavan Sukhdev , General Manager Deutsche Bank (2011)

So far, ecological values ​​have hardly been included in economic or business accounts (see ecological footprint ). The main causes of species extinction today are:

  • The destruction of natural habitats: According to the findings of ecological research, the biodiversity of a habitat depends directly on its area. If a habitat is reduced in size through human activities, for example through deforestation, it loses part of its species population. How many and which species will become extinct is difficult to predict in detail (relationship via so-called species-area curves that differ between different habitats). Predictions of today's species extinction are hardly ever based on direct evidence of the extinction of individual known species, but are essentially derived from this context.
  • Overuse , e.g. B. Overfishing , overgrazing and uncontrolled hunting or gathering: ecosystems degrade through overuse. How much ecosystems that are widely considered to be natural have already changed is shown by Jackson, for example, using the Atlantic coastal waters as an example.
  • Pollution: During the past 4 decades, e.g. For example, the worldwide pesticide consumption tripled to 2.5 million tons annually, 50,000 different chemicals are in use. Residues of these and other chemicals are found in natural ecosystems. Effects on natural communities are difficult to assess.
  • Climate change : Changes in species areas as a result of climatic changes are in principle a natural process. One of the threats to man-made climate change is the extreme pace of change (viewed in natural periods), which could overwhelm the adaptability of many species. In addition, fatal interactions between climate change and habitat destruction are to be assumed. Possible refuge spaces are not available due to human use or cannot be reached due to biotope fragmentation. In addition, the network of designated protected areas may no longer match the changed areas of the species.
  • The displacement of indigenous species by invasive species: Species losses due to introduced species have devastated island ecosystems in particular on a large scale. In a classic article, Pimm et al. Point to the loss of bird species from the Polynesian islands by the immigrating Polynesians and the rats introduced with them: a loss of around 2,000 bird species (around 15% of the world's fauna) can be assumed. Locally, biodiversity can even increase due to neobiota . In Central Europe and also in the North Sea, the invasion of numerous heat-loving species is observed, which are increasingly establishing themselves as a result of climate change. In the eastern Mediterranean, the number of species is constantly increasing due to immigration from the Red Sea via the Suez Canal , which is exacerbated by the warming of the Mediterranean water. These phenomena are the result of the global intermingling of previously separate fauna and flora and lead to homogenization and thus impoverishment worldwide.
  • Extinction due to introduced pathogens. In recent years it has been discussed that the extinction of numerous amphibian species that can be observed worldwide can be traced back, among other things, to a pathogen, chytridiomycosis , which was carried around the world by clawed frogs from Africa . Other known cases involve North American and Eurasian tree species. In general, little is known about this factor.

Biodiversity may well increase locally and regionally at the moment; this is not in contrast to the extinction of species on a global level and does not mean that the global extinction of species has come to a standstill. Numerous wild populations on earth and in the waters have shrunk to small and extremely small population sizes and are therefore subject to an increased risk of extinction.

Biodiversity, Stability, and Disturbances

To illustrate the importance of biodiversity, different visual models are propagated, including the following:

  • Rivet hypothesis : Each rivet on an aircraft fuselage contributes to holding together and thus prevents the aircraft from crashing: Each type is more or less important for maintaining an ecosystem.
  • Passenger hypothesis : No passenger is required for the aircraft to fly, but the crew all the more : only a few key types are important .

The importance of biodiversity for the stability of ecosystems is a topic in ecological science that has been controversially discussed for more than 80 years, the so-called “diversity-stability” controversy (overview with regard to modern applications, for example). The fact that the term "stability" was defined more precisely helped to clarify the situation (Grimm and Wissel found 163 different definitions of stability in a literature study, which referred to 70 concepts.) Today (according to Pimm 1984), a distinction is usually made between: persistence ( one observes little changes in observations over a long period of time), resilience (the system returns to its original state after disruptions), resistance (the system remains unchanged for a long time in the event of disruptions). Research results indicate that the temporal stability (i.e. the persistence) increases with the higher number of species. Whether this also applies after disruptions (i.e. resilience) is controversial. Species diversity may be of minor importance for the resilience of a particular ecosystem or even decline, but this could be reversed at a higher level.

According to the Intermediate Disturbance Hypothesis (IDH) by Joseph H. Connell (University of California), some ecosystems react to slight, regular disturbances (e.g. fires, storms , floods ) with increasing biodiversity. Areas occupied by certain species become vacant as they disappear due to the disturbance. This space can be reoccupied by other (possibly not yet present) species (including so-called pioneer species ). As a result, the number of species and thus the diversity of species increases. However, this principle of the mean frequency of disturbances does not apply without restrictions to every system, i.e. not every system increases the diversity of species due to disturbance, but can also behave in the opposite way. The model for the connection between biodiversity and disturbances that is accepted by most ecologists today is the “dynamic equilibrium model”. According to this, the number of species in highly productive ecosystems increases with increasing disturbance (mainly because it counteracts the exclusion of competition). In less productive systems, however, it sinks (because the slowly growing species react more sensitively). In highly productive systems (such as over-fertilized lakes), biodiversity is minimal even when there is a high level of disturbance (the so-called “enrichment paradox”).

Programs and instruments to conserve biodiversity

In the past, some species have been preserved through zoos and re-breeding programs. Successful examples of the 20th century are the European bison , the David deer , the Przewalski horse and, since 2003, the tree lobster . However, attempts to save species outside of their natural habitat (e.g. in zoos and botanical gardens or seed banks) cannot save all species, since many animals do not reproduce in captivity and there is hardly any capacity to take up other species. Resettlement / reintroduction is also time-consuming. In contrast, the designation of protected areas (e.g. nature reserves ) is a good solution (e.g. with the help of the modern instrument of gap analysis ), although these are most successful when all interest groups can be integrated.

The Global Environment Facility (GEF), into which the industrialized countries contribute, is an instrument for nature conservation measures and for the careful use of natural resources in poorer countries . The economically viable sustainable use also safeguards nature. So z. For example, the Forest Stewardship Council (FSC) sets criteria for environmentally compatible forest use , according to which 150,000 km² of forest have already been designated in almost 30 countries. The condition for further success is the acceptance of the consumer for certified (and possibly more expensive) wood products.

The Washington Convention on the Protection of Species (CITES) has been regulating international trade in endangered species of wild animals and plants and their products since 1973 . At the 15th meeting of the Conference of the Signatory States (CoP15) in Doha, Qatar , from 13-25 March 2010, the participants could neither agree on a short-term ban on the trade in bluefin tuna for the recovery of stocks, nor on a trade ban in polar bear skins or the protection of various species of sharks such as hammerheads and dogfish, some of which are products under the names Schillerlocke , Kalbsfisch, Sea eels or sea sturgeon are also on the market in Europe. In contrast, the trade ban on ivory was extended.

As early as 2010, the EU wanted to achieve the goal of preventing animal and plant species from becoming extinct in Europe. On March 15, 2010, the EU environment ministers postponed this target to 2020 and started a biodiversity campaign. Due to the intensification of agriculture - accelerated by the subsidies of the EEG - the area pressure in parts of Germany has become very high, so that every area is used very intensively.

In 2020, researchers used rough models to show how the UN Sustainable Development Goals on biodiversity can be achieved while ensuring that the world's population is fed. Trends could be turned positive by 2050 through an integrative strategy and immediately starting “efforts that are consistent with the broader sustainability agenda, but of unprecedented ambition and coordination” - for example through sustainable efficiency improvements in agriculture and more plant-based nutrition become.

UN wildlife conservation conferences

2010: "International Year of Biodiversity"

The General Assembly of the United Nations (UN) decided in December 2006 to declare 2010 the International Year of Biodiversity . She did so out of concern about the social, economic, ecological and cultural consequences of biodiversity loss and with the hope that states and other actors would use this opportunity to raise awareness of the importance of biodiversity and take local, regional and international action perform. The activities are coordinated by the Secretariat of the Convention on Biological Diversity in Montreal , Canada.

"UN Decade of Biological Diversity 2011–2020"

The UN Decade of Biological Diversity 2011–2020 is an emphatic initiative of the United Nations for the global conservation of biological diversity: in a declaration, all states were called upon to undertake additional activities for the benefit of biodiversity and thus to implement the CBD goals during the decade .

See also


  • Bernhard Schmid: The functional importance of biodiversity. In: Biology in Our Time. 33, No. 6, 2003, pp. 356-365.
  • Bruno Streit : What is biodiversity? Exploration, protection and value of biodiversity. CH Beck, Munich 2007.
  • Jonathan EM Baillie, Janine Griffiths, Samuel T. Turvey, Jonathan Loh, Ben Collen: Evolution Lost. Status and Trends of the World's Vertebrates. The Zoological Society of London, 2010, ISBN 978-0-900881-41-1 . ( download ; PDF; 7.3 MB)

Web links

Wiktionary: biodiversity  - explanations of meanings, word origins, synonyms, translations

Individual evidence

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