Species - SpeedyLook encyclopedia

Formal presentation

In the scientific Classification, an alive species (or having lived) is indicated by a binomial Latin, composed of a generic name (which takes a initial Majuscule) followed of one or two epithet specific. For example, the human beings belong to the kind Homo and the species Homo sapiens . The name of the species is the whole of the binomial and not only the specific epithet. Formalized by Carl von Linné during the 18th century, the Nomenclature binominale, as well as other formal aspects of the biological nomenclature, constitutes the “system linnéen”.

The scientific names “are famous Latin S” and are written in Italique. When one refers to a nongiven species (not identified) but whose kind is known, it is of use to use as provisional epithet the abbreviation of species , “ Sp. ” in the singular (and “ Spp. ” in the plural) following the name of kind; in the same way, “subspecies” is shortened in “ Ssp. ” in the singular (and “ Sspp. ” in the plural). These abbreviations are written in Roman characters .

Problems of the concept of species

At the 18th century, the species were regarded as the result of divine creation and, for this reason, were regarded as objective and immutable realities.

Since the advent of the theory of the evolution, the concept of species biological appreciably evolved/moved, but no consensus could be obtained on its definition.

The definition most commonly quoted is due to Ernst Mayr. According to this definition, which is that of the concept of species biological (or isolated species), the species are “groups of Population S Naturelle S, indeed or potentially interfécondes, which is genetically isolated from other similar groups”. But as one as well finds reproduction asexual (or a parthenogenesis) in the animals as at the plants and in almost all the groups of animals (fish, reptiles, batrachians, insects), the concept of species cannot be related to the interfertility any more.

Many other definitions also have course for example the species can be defined as a population whose members can cross without difficulties under conditions Naturelle S.

Another definition rests on the concept of resemblance (or contrary to degree of difference), concept still very much used in Paléontologie, where there is not an other option. Certain authors use even these two principles to define the species.

The study of DNA nowadays makes it possible to seek nonvisible resemblances directly on the physical level (Phénotype). But the quantitative criterion (many identical genes) mask the qualitative criterion, by nonmeasurable definition. Thus, the classification of the Orchises of the Ophrys type emphasizes a great number of species, obviously different (thus from the point of view Phénotype) whereas their Génotype S appeared very close.

The biological species is generally defined today like a reproductive Communauté (interfecondity) of populations. If this definition lends itself rather well to the Animal kingdom, it is less obvious in the Vegetable kingdom, where frequently occur Hybridation S. One often associates the double criterion of meeting by Interfécondité and separation by non-interfecondity, to ensure the perpetuation of the species.

A question deserves to be posée : does the concept of species constitute a simple convenience of work or it has a reality independent of our system of classification ? Does it have a true significance in the absolu ? The species to which laws are universally applicable, or has a logical class same reality as an individual (by chalk-lining)? The answers to these considerations concern the epistemology and the operational Sémantique as much as Biologie.

The problem becomes complicated because of the questions of interfecondity present or goes away, and not always as distinct as in the manuels : populations A₁, A₂ can be interfécondes, like A₂ and A₃…. and A_n-1 and A_n and one can have at one time of the populations A₁ and A_n which is not (it is to it case of variation clinale or species boxing ring which is brought back by Konrad Lorenz at the seagulls . The concept of species then dissolves in a kind of fuzzy).

The interfecondity thus does not make it possible to say that they are same species while the non-interfecondity is enough to say that they are different species. This non-interfecondity must be also and especially required in the descendants : horses and asses are interféconds but their hybrids (mule and mule, shingle or bardot) are it seldom. The two populations thus form different species.

In the same way, certain races of dogs ( Canis familiaris ) are hybrident without problem - and have a fertile descent - with common wolves ( Canis lupus ), while their hybridization with other races of their own species Canis familiaris remains quite problematic - in the case for example of a Chihuahua female and a Saint-Bernard male;!

That is explained by two faits : the domestic dog is very polymorphic and it is an artificial selection starting from wolves - there is now genetic evidence. One should thus name it Canis lupus familiaris , i.e. a subspecies of the Wolf thus perfectly interfécond with him… within the limit of what allows physically the receiving uterus.

Evolution of the concept of species during time

The stockbreeders had of it probably a notion not formalized since the origin even of the breeding. Plato will speculate that since one sees horses and cows, but never of hybrid of both, it must exist some share a ideal form which constrained an animal with being one or the other. Aristote will for its part prefer to avoid these speculations and to be satisfied to index in Organon what it observes. Albert Large the will be tested there in its turn later.

Empirical concept, the concept of species evolved/moved with time and its history was marked by the thought of large naturalists like Linné, Buffon and Darwin.

Initially, one regarded the species as fixed entities defined by morphological criteria. This typological design found its apogee with work of Linné and the establishment of collections of individuals “ typiques ” of the species.
According to Vat, a species can be defined like the collection of all the organized bodies born from/to each other or common parents and those which resemble to them as much as they do not resemble between them .
This design evolved to a species “ taxonomique ” for which the mathematical analysis of a great number of criteria would be enough to establish a threshold from which one could say that two individuals belong to different species. The species would be then more one concept convenient that a real biological entity.
the insufficiencies of this method led to another approach which is the concept of primarily founded biological species on the criteria of interfecondity and insulation (Ernst Mayr, 1942), with there still some difficulties to differentiate for example from the species which are not naturally in contact, etc
This resulted in amending this definition of the species by including an ecological component there. As from 1963, Ernst Mayr thus defines the species as a reproductive community of Population S, reproductivement isolated from other communities and which occupies a particular niche in the Nature . This operational definition of the species is not however free from problems (for example, recognition of the niches).
most of these problems can be prevented if the history of the living beings is considered. The evolution is a historical process and the species are the result of the bursting of species which preceded them (Spéciation). All the preceding criteria must be correlated with the genealogical relations.

a species is thus a simple chalk-lining which has its own evolutionary tendencies and its own historical destiny (according to Delforge P Guide of the Orchises of Europe… Delachaux and Niestlé 1994). Concept of “ Destiny ” no base scientifique has;: “its own history” not only would be appropriate well better but moreover, it is what seek to discover number of scientifiques ! The concept of “simple chalk-lining” must also be moderate because, as one saw, a certain interfecondity remains possible between certain species proches : it can result from it from the fertile descendants to the characteristics more adapted to their medium which will perhaps form with time a species with whole share.

Subspecies

Within a species given, a subspecies consists of a group of individuals who are insulated (for reasons ecological S, Anatomique S or Organoleptique S) and which evolves/moves apart from the genetic current of the species of reference.

At the end of a certain time, this group of individuals takes specific characteristics which differentiate it from the species of reference. These characters can be new (appearance following a change for example) or be the fixing of a variable characteristic at the species of reference.

Different subspecies often have the possibility of reproducing between them, because their differences (still) are not marked.

The rules of the Nomenclature want that, the first time that a species is divided into subspecies, the subspecies which corresponds to the specimens which were used to describe the “standard” species, takes a second of the same epithet automatically name than that of the species. This trinomial is known as autonomous (or nominal ), because it does not require the publication of a new diagnosis.

Thus, in Zoologie the subspecies of reference of Tarentola mauritanica will be indicated under the name of Tarentola mauritanica mauritanica each time one needs to distinguish it. The other subspecies (which will have to be the subject of a description validly published) will have an obligatorily different final epithet: for example Tarentola mauritanica fascicularis .

Since approximately 1960, one uses more and more designation “ formed ”, shortened “ F. ”, which expresses clearly that it is about the shape of pet which can possibly go up to various wild subspecies: Capra aegagrus F. hircus .

In Botanical and Mycology, the two epithets after the name kind must be separated by the shortened indication of the row (cut) infraspecific: Subsp. or Ssp., VAr. or V., Fo. or F., respectively meaning subspecies, varietas and formed . For example: ''Agaricus bisporus'' fo. ''bisporus'' .

The row of form (fo.) will be used to indicate an entity of row lower than the species and the variety. The form being the smallest taxinomic cut in the Systematic and the Classification of the alive world, nearest to the “involved individual”. For example, when we say that we have in our plate the “white form” of the Cultivated mushroom , we make same division empirically as the mycologist who named it by the Trinôme Agaricus bisporus fo. alba .

More still than the varietal row, the choice of the formal row indicates that the population of individuals thus circumscribed differs from the “standard” species only by one or more characters considered as minor on a plan taxinomic (morphological characteristic , ecological, Organoleptique, etc), like the “white color” in our example. One can wonder about the validity of the definition of a subspecies knowing that the definition of the term species remains fluctuating and discussed. It is the same here and all the limits of the definition of a species also apply for that of a subspecies.

How much species?

For Carl von Linné, at the 18th century, the world counted approximately 67.000 different species. Today, nobody can define with precision the number of species existing on planet.

Whereas one estimates at approximately 13-14 million the number of alive species on planet, only a tenth (pilot of the difficulties related to the concept of species, the number itself of described species remains vague, between 1,5 and 1,8 million) was described scientifically.

The great majority of the not described species are Procaryote S (Archea and Eukarya) and unicellular Eucaryote S, Protozoaire S like the Algue S, certain ex-mushrooms now classified in the Straménopiles, or of the Myxomycètes (now classified in several groups of protists…).

In 2006, according to the red List of the UICN, the identified species can be broken up as follows:

287,655 Plant S, of which:

15,000 foams,
13,025 ferns,
980 Gymnospermes,
199,350 Dicotylédone S,
59,300 Monocotylédone S;

74,000-120,000 mushrooms, of which:

32,000 ascomycètes,
17,000 basidiomycetes;

10,000 Lichen S;
1,250,000 animal, of which:

1,190,200 Invertebrate S:

950,000 Insect S,
70,000 molluscs,
40,000 Crustacean,
130,200 others;

58,808 Vertebrate:

29,300 Poisson S,
5,743 Amphibians,
8,240 Reptiles,
10,234 Bird X, (9799 existing in 2006)
5,416 Mammalian S.

Approximately 10.000 new species are described each year. It is which also disappears because of man (see Dodo, genetic Diversité…), and others finally eliminated by climate changes from the niche where they lived.

See too

Homo sapiens
domesticated Species - extirpated Species - vulnerable Species - threatened Species - Species in danger of disappearance - disappeared Species - new Species - invasive Species
Natural;
Humanity - Mankind - Homo sapiens
Race or human Race
Speciation
Theory of the evolution

External bonds

Wikispecies (repertory of alive)
the species are threatened on Earth
does one Have to give up the concept of espèce ? by Herve Guyader
Evolution of alive (Debate between Bernard Brun, Jacques Ninio and Jean−François Gerard to be downloaded in pdf

Random links:

Kativik | Deep field of Hubble | Georges Rossi | Hickstead | Lake-Nilgaut