Classification of species

In traditional classification, or phylogenetics, species is the taxon base of systematic, whose rank is just below the type.

Scientific classification

In scientific classification, a species living or having lived is designated following the rules of binomial nomenclature, established by Carl von Linne in the eighteenth century. According to this classification, the name of a species consists of a binomial Latin name that combines the genre with one or two specific epithets. Whenever possible, the name is followed by the citation of the author's name, abbreviated (in botany) or full (in zoology), who first described the species under that name. The species name is the whole binomial, not just the specific epithet.

For example, humans belong to the genus Homo and the species Homo sapiens.

Scientific names are "famous" Latin and written in italics. The genus is capitalized, while the original specific epithet is entirely in lowercase. When the name of the author is quoted in full, it is italicized.

When the genus is known but the species is not determined, it is customary to use as an epithet provisional abbreviation of Latin species "sp." Following the genus name. When you want to nominate several species or all species of a genus is the abbreviation "spp." (For species pluralism) is added. Similarly, "subspecies" is abbreviated as "ssp." (For sub-species) and "sspp." Plural (for sub-species pluralism). These abbreviations are always written in Roman characters.

The binomial nomenclature, and other formal aspects of biological nomenclature, is the "Linnean system. This system of nomenclature used to define a unique name for each species, valid worldwide, unlike the classification vernacular.

Subspecies

 Wagtail, Motacilla alba alba

Wagtail, Motacilla alba alba

 Yarrell Wagtail, Motacilla alba yarrellii   Wagtails Both males were described as two different subspecies within a species: Motacilla alba.


Yarrell Wagtail, Motacilla alba yarrellii

Wagtails Both males were described as two different subspecies within a species: Motacilla alba.

Within a given species, a subspecies is a group of individuals who are isolated (for geographical, ecological, anatomical or sensory) and move outside the current gene of the indicator species.

After a while, this group of individuals taking specific features that differentiate the species of reference. These characters may be new (onset following a mutation for example) or be setting a characteristic variable in the indicator species.

The different subspecies are often able to reproduce them, because their differences are not (yet) sufficiently marked to constitute a reproductive barrier.

One can question the validity of the definition of a subspecies that knowing the definition of species remains fluid and controversial. It is here as well and all terms of the definition of a species that also apply to a sub-species.


Identification of species

Carl von Linne identifying the eighteenth century about 67 000 different species. Today, no one can define with precision the number of species on the planet.

While it is estimated that between 5 and 30 million living species on the planet only 1.5 to 1.8 million species have been scientifically described (witness the difficulties the concept of species This number itself is unclear). Marine species make up only 13% of all described species, approximately 275 000, including 93 000 for the only coral reef ecosystems

The vast majority of undescribed species are insects (4 to 100 million species according to estimates, who live mainly on the canopy of tropical forests the Nemathelminthes (or roundworms: 500 000 to 1 000 000 'species), prokaryotes (Arche and Eukarya) and eukaryotic unicellular organisms: protozoa or Protophyta some former mushrooms now classified as Straménopiles or Myxomycetes (now classified in several groups of protists ...).

According to red list of IUCN in 2006 and the most recent data, described living species can be decomposed as follows:
 
Described species and undescribed some groups of living
312 655 plants, including:
25 000 algae,

15 000 mosses,
13 025 ferns,
980 gymnosperms,
199 350 Broadleaf,
59 300 monocotyledons;
74 000-120 000 fungi, including:
32 000 ascomycetes,
17 000 basidiomycetes;
10 000 lichens;
1 500 000 animals:
30 000 Protozoa,
1 440 000 invertebrates, including:
1 100 000 arthropods, 950 000 insects 80 000 spiders 55 000 crustaceans 13 000 myriapods ...
120 000 molluscs 100 000 gastropods 15 000 bivalves 850 cephalopods ...
80 000 round worms
20 000 flatworms (75% of parasites)
15 000 annelids
10 000 cnidarians
9 000 sponges
7 000 echinoderms
5 700 bryozoans
2 500 tunicates
60 516 vertebrates:
108 Agnatha (lampreys and hagfish)
900 cartilaginous fish (sharks, rays and chimeras)
30 000 bony fish
5 743 amphibians
8 240 reptiles,
10 234 birds,
5 416 mammals.

About 16 000 new species are described each year, of which 1 600 marine species Approximately 10 species disappear naturally (ie, outside of the intervention of humans) each year but it is also disappearing because of man (see Dodo , Genetic diversity ...): Edward O. Wilson estimates the number at several thousand per year According to the Evaluation of the Millennium Ecosystem of 2005, the current rate of extinction of species is at least 1 000 times the natural rate, estimated over the last 10 million years.

Read also: Concept of the species: Biological Concept and Other concepts


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