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- This article discusses biological species. Also see combinatorial species for the mathematical meaning of the term.
- Species is also a movie by Roger Donaldson.
- In English "species" is both singular and plural. The word " specie" is unrelated and is used to refer to coins, or in chemistry as a molecule, ion, atom, or free radical (and in which case "species" means a pair of identical such particles).
In biology, a species is a kind of organism. Loosely speaking, a species is a related group of organisms that share a more or less distinctive form and are capable of interbreeding. As defined by Ernst Mayr, species are "groups of actually or potentially interbreeding natural populations which are reproductively isolated from other such groups" (however, see definitions of species below). In scientific classification, a species is designated by a binomial written in italic text and consisting of the genusSee genus (mathematics) for the use of the term in mathematics. See genus (music) for the use of the term in music. In biology, a genus (plural genera is a grouping in the classification of living organisms having one or more related and morphologically s name followed by a unique descriptor. It is the binomial that is the species name, not the second term in the binomial. For example, two related species of lobstersHomarus is a genus of lobster from the phylum Arthropda, which include the common and commercially significant species American Lobster Homarus americanus and the European Lobster Homarus gammarus . are Homarus americanus and Homarus gammarus. It would be incorrrect to say americanus and gammarus are two species in the genus HomarusHomarus is a genus of lobster from the phylum Arthropda, which include the common and commercially significant species American Lobster Homarus americanus and the European Lobster Homarus gammarus ., just as it would be incorrect to say "Monterey" is a species of pine ( MontereyMonterey is a city near the Pacific coast in northern California. It is located in Monterey County. As of 2000, the population was 29,674. The city calls itself "The Cradle of History. Monterey was the capital of California from 1777 to 1849, under the fl is a place in CaliforniaCalifornia is a state located in the western United States, bordering the Pacific Ocean. The most populous and third largest state in the U. California is both physically and demographically diverse. The state's official nickname is "The Golden State", wh)—the tree is a Monterey pine. Thus, Homarus americanus is the species name for what is commonly called a MaineMaine is a state of the United States. It is probably named after the French province of Maine. Another possibility for the name 'Maine' is that the people living on islands along the coast of Maine used to speak of going to the mainland as 'going over to lobster.
1 Definitions of species
The definition of a species given above as taken from Mayr, is somewhat idealistic. Since it assumes sexual reproduction, it leaves the term undefined for a large class of organisms that reproduce asexually. Biologists frequently do not know whether two morphologically similar groups of organisms are "potentially" capable of interbreeding. Further, there is considerable variation in the degree to which hybridization may succeed under natural and experimental conditions, or even in the degree to which some organisms use sexual reproduction between individuals to breed. Consequently, several lines of thought in the definition of species exist:
- A morphological species is a group of organismIn biology and ecology, an organism is a living being. The origin of life and the relationships between its major lineages are controversial. Two main grades may be distinguished, the prokaryotes and eukaryotes. The prokaryotes are generally considered tos that have a distinctive form: for example, we can distinguish between a chicken and a duck because they have different shaped bills and the duck has webbed feet. Species have been defined in this way since well before the beginning of recorded history. Although much criticised, the concept of morphological species remains the single most widely used species concept in everyday life, and still retains an important place within the biological sciences, particularly in the case of plants.
- The biological species or isolation species concept identifies a species as a set of actually or potentially interbreeding organisms. This is generally the most useful formulation for scientists working with living examples of the higher taxa like mammals, fish, and birds, but meaningless for organisms that do not reproduce sexually. It distinguishes between the theoretical possibility of interbreeding and the actual likelihood of gene flow between populations. For example, it is possible to cross a horse with a donkey and produce offspring, however they remain separate species—in this case for two different reasons: first because horses and donkeys do not normally interbreed in the wild, and second because the fruit of the union is rarely fertile. The key to defining a biological species is that there is no significant cross-flow of genetic material between the two populations.
- A mate-recognition species is defined as a group of organisms that are known to recognise one another as potential mates. Like the isolation species concept above, it applies only to organisms that reproduce sexually.
- A phylogenetic or evolutionary or Darwinian species is a group of organisms that shares an ancestor; a lineage that maintains its integrity with respect to other lineages through both time and space. At some point in the progress of such a group, members may diverge from one another: when such a divergence becomes sufficiently clear, the two populations are regarded as separate species.
- See also microspecies under apomixis, for species that reproduce without meiosis or mitosis so that each generation is genetically identical to the previous generation.
In practice, these definitions often coincide, and the differences between them are more a matter of emphasis than of outright contradiction. Nevertheless, no species concept yet proposed is entirely objective, or can be applied in all cases without resorting to judgement.
