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from Latin: species - kind, shape
German: Art (Biologie)

1 Definition

In biology a species is defined as the taxonomic rank directly below the genus.

2 History

The term species can be found in early antiquity. Under the term existentialistic taxonomy, Aristotle, Plato and later Carl von Linné took up the species term. It gained particular importance when Charles Darwin discovered a multitude of new species, especially on the Galapagos Islands, and postulated the development of new species from existing ones by evolution.

Nearly 2 million species are known today, of which a quarter are plant species. It is estimated that there is a total of over 1.6 billion eukaryotic species. The number of prokaryotes is estimated at a twelve-digit number [1].

3 Nomenclature

Different synonyms and abbreviations exist in connection with the biological term of species which are used differently and have non-identical meanings:

  • The species designates the taxonomic level below the genus. Species are named according to a binary nomenclature consisting of the uppercase genus name and the lowercase species name. Homo sapiens therefore means the species sapiens, which belongs to the genus Homo.
  • The abbreviation spp. is used for all members of a genus, e.g. Staphylococcus spp. for all Streptococcus species.
  • The abbreviation sp. or spec. is added for a not further decribed organism of which the genus is clear, e.g. Bacillus sp.. This also applies to species who are not yet defined or described sufficiently.
  • When describing new species for the first time ("nova species"), the suffix n.sp., rarely nov. spec. is added.
  • Species can also be further categorised as subspecies, in short ssp. or subsp.. This is done for those organisms who are clearly assigned to a certain species but nevertheless show differences in habitat or morphology. An example is Canis lupus arctos, or Canis lupus ssp. arctos.

The species nomenclature is nowadays based on the rules of internationally recognised codes. These exist for plants (incl. fungi) [2], animals [3], bacteria) [4], cultivated plants [5] and viruses [6] (allthoght they are not living organisms from a biological point of view).

4 Classification

There are several classification systems that classify species as such. Some of them are listed here:

  • morphological species concept: Species are identified by morphological, but also behavioural aspects. It is used in Ecology, Botany, Zoology and Palaeontology. In the case of prokaryotes, the metabolism is included as an additional characteristic for distinguishing the species. Species classified according to this concept are called morphospecies.
  • population genetics species concept: Here, a species is understood as a group of natural populations that can mate successfully and is reproductively isolated from other groups.
  • phylogenetic or evolutionary species concept: Species are defined by a beginning and an end. The species thus begins with them emerging from another species and ends when all representatives of the species, without leaving any descendants, die out or new species emerge from it.
  • molecular genetics species concept: Sequence differences of certain marker genes are used for the determination of relatedness. The method is mainly used for prokaryotes, as the other concepts are only partially effective here. A frequently used marker gene is that for the 16S-rRNA subunit. It is a gene in bacteria and Archaea which has preserved and variable regions. The latter are used to determine sequence homology. From a homology of 97% on, prokaryotes are considered to belong to the same species.

5 Problematics

Each of the species concepts listed above has its own problems. Often the definition of a species is "fuzzy" and influenced by inaccuracies. Even the species concepts themselves are not exactly defined in some parts and are therefore subject to subjective interpretations. With prokaryotes, horizontal gene transfer, high mutation rates, and short doubling times are additional complications when determining the species.

In addition, the division into groups according to only one concept can lead to problems, for example in the determination of species on the basis of purely phenotypic characteristics. These can be due to phenotypic plasticity, as it is often the case with plants, and not due to species formation. Other natural phenomena such as polymorphisms, sexual dimorphisms, hybrids and transitional forms, ring- and cryptospecies make a clear classification into species more difficult.

The concept of species and how it is defined is therefore still the subject of discussion in science today.

6 References

  1. Locey KJ, Lennon JT:Scaling laws predict global microbial diversity Proc Natl Acad Sci U S A. 2016 May 24;113 (21): 5970-5. doi: 10.1073/pnas. 1521291113.
  2. International Code of the Nomenclature for Algae, Mushrooms and Plants (ICN)
  3. org/ International Rules for the Zoological Nomenclature
  4. code of the bacterial nomenclature
  5. International Code of the Cultivated Plants Nomenclature
  6. International Code of the Virus Nomenclature

Specialties: Biology

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