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105-414:  • Callisitta formosa (Blyth, 1943) The beautiful nuthatch ( Sitta formosa ) is a bird species in the family Sittidae , collectively known as nuthatches . It is a large nuthatch, measuring 16.5 cm (6.5 in) in length, that is not sexually dimorphic . Its coloration and markings are dramatic, the upper parts being black and azure , streaked with white and pale blue on

210-506: A binary tree ), and an unrooted bifurcating tree takes the form of an unrooted binary tree , a free tree with exactly three neighbors at each internal node. In contrast, a rooted multifurcating tree may have more than two children at some nodes and an unrooted multifurcating tree may have more than three neighbors at some nodes. Both rooted and unrooted trees can be either labeled or unlabeled. A labeled tree has specific values assigned to its leaves, while an unlabeled tree, sometimes called

315-423: A mutation–selection balance . It is predicted that a viral quasispecies at a low but evolutionarily neutral and highly connected (that is, flat) region in the fitness landscape will outcompete a quasispecies located at a higher but narrower fitness peak in which the surrounding mutants are unfit, "the quasispecies effect" or the "survival of the flattest". There is no suggestion that a viral quasispecies resembles

420-412: A phylogeny based on examination of nuclear and mitochondrial DNA of 21 nuthatch species. The position of the beautiful nuthatch within the genus was not established with certainty, having a far lower statistical association than others in the model. Nevertheless, under the findings the species appears closest evolutionarily to three clades of nuthatches: two nuthatches that prefer rocky environments,

525-480: A rooted phylogenetic tree, each node with descendants represents the inferred most recent common ancestor of those descendants, and the edge lengths in some trees may be interpreted as time estimates. Each node is called a taxonomic unit. Internal nodes are generally called hypothetical taxonomic units, as they cannot be directly observed. Trees are useful in fields of biology such as bioinformatics , systematics , and phylogenetics . Unrooted trees illustrate only

630-400: A "classical" method of determining species, such as with Linnaeus, early in evolutionary theory. However, different phenotypes are not necessarily different species (e.g. a four-winged Drosophila born to a two-winged mother is not a different species). Species named in this manner are called morphospecies . In the 1970s, Robert R. Sokal , Theodore J. Crovello and Peter Sneath proposed

735-424: A 'smallest clade' idea" (a phylogenetic species concept). Mishler and Wilkins and others concur with this approach, even though this would raise difficulties in biological nomenclature. Wilkins cited the ichthyologist Charles Tate Regan 's early 20th century remark that "a species is whatever a suitably qualified biologist chooses to call a species". Wilkins noted that the philosopher Philip Kitcher called this

840-572: A Fokienia evergreen ( Fokienia hodginsii ) – a tree frequently enveloped in epiphytes. The bird has been described at times as the most timid of nuthatches. It prospects in a manner typical of many others in its genus, sometimes hanging upside down for an extended time surveying its surroundings. As compared with other nuthatch, the species has been described as working "unhurriedly", as they peck at trunks, lichen and other epiphytes, searching for prey. Stomach contents of collected Chinese specimens consisted of beetles and insect larvae . Reproduction in

945-515: A black eyestripe. Sitta is derived from the Ancient Greek name for nuthatches, σίττη , sittē . " Nuthatch ", first recorded in 1350, is derived from "nut" and a word probably related to "hack", since these birds hack at nuts they have wedged into crevices. The genus may be further divided into seven subgenera , of which the beautiful nuthatch is placed alone in Callisitta (Bonaparte, 1850), and

1050-409: A clear outgroup. Another method is midpoint rooting, or a tree can also be rooted by using a non-stationary substitution model . Unrooted trees illustrate the relatedness of the leaf nodes without making assumptions about ancestry. They do not require the ancestral root to be known or inferred. Unrooted trees can always be generated from rooted ones by simply omitting the root. By contrast, inferring

1155-814: A combination of genes that come from different genomic sources (e.g., from mitochondrial or plastid vs. nuclear genomes), or genes that would be expected to evolve under different selective regimes, so that homoplasy (false homology ) would be unlikely to result from natural selection. When extinct species are included as terminal nodes in an analysis (rather than, for example, to constrain internal nodes), they are considered not to represent direct ancestors of any extant species. Extinct species do not typically contain high-quality DNA . The range of useful DNA materials has expanded with advances in extraction and sequencing technologies. Development of technologies able to infer sequences from smaller fragments, or from spatial patterns of DNA degradation products, would further expand

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1260-428: A connected series of neighbouring populations, each of which can sexually interbreed with adjacent related populations, but for which there exist at least two "end" populations in the series, which are too distantly related to interbreed, though there is a potential gene flow between each "linked" population. Such non-breeding, though genetically connected, "end" populations may co-exist in the same region thus closing

1365-432: A different species from its ancestors. Viruses have enormous populations, are doubtfully living since they consist of little more than a string of DNA or RNA in a protein coat, and mutate rapidly. All of these factors make conventional species concepts largely inapplicable. A viral quasispecies is a group of genotypes related by similar mutations, competing within a highly mutagenic environment, and hence governed by

1470-427: A function of the number of tips. For 10 tips, there are more than 34 × 10 6 {\displaystyle 34\times 10^{6}} possible bifurcating trees, and the number of multifurcating trees rises faster, with ca. 7 times as many of the latter as of the former. A dendrogram is a general name for a tree, whether phylogenetic or not, and hence also for the diagrammatic representation of

1575-508: A genetic boundary suitable for defining a species concept is present. DNA barcoding has been proposed as a way to distinguish species suitable even for non-specialists to use. One of the barcodes is a region of mitochondrial DNA within the gene for cytochrome c oxidase . A database, Barcode of Life Data System , contains DNA barcode sequences from over 190,000 species. However, scientists such as Rob DeSalle have expressed concern that classical taxonomy and DNA barcoding, which they consider

1680-465: A lineage should be divided into multiple chronospecies , or when populations have diverged to have enough distinct character states to be described as cladistic species. Species and higher taxa were seen from the time of Aristotle until the 18th century as categories that could be arranged in a hierarchy, the great chain of being . In the 19th century, biologists grasped that species could evolve given sufficient time. Charles Darwin 's 1859 book On

1785-492: A misnomer, need to be reconciled, as they delimit species differently. Genetic introgression mediated by endosymbionts and other vectors can further make barcodes ineffective in the identification of species. A phylogenetic or cladistic species is "the smallest aggregation of populations (sexual) or lineages (asexual) diagnosable by a unique combination of character states in comparable individuals (semaphoronts)". The empirical basis – observed character states – provides

1890-609: A more suitable metaphor than the tree . Indeed, phylogenetic corals are useful for portraying past and present life, and they have some advantages over trees ( anastomoses allowed, etc.). Phylogenetic trees composed with a nontrivial number of input sequences are constructed using computational phylogenetics methods. Distance-matrix methods such as neighbor-joining or UPGMA , which calculate genetic distance from multiple sequence alignments , are simplest to implement, but do not invoke an evolutionary model. Many sequence alignment methods such as ClustalW also create trees by using

1995-536: A number of different formats, all of which must represent the nested structure of a tree. They may or may not encode branch lengths and other features. Standardized formats are critical for distributing and sharing trees without relying on graphics output that is hard to import into existing software. Commonly used formats are Although phylogenetic trees produced on the basis of sequenced genes or genomic data in different species can provide evolutionary insight, these analyses have important limitations. Most importantly,

2100-449: A particular species, including which genus (and higher taxa) it is placed in, is a hypothesis about the evolutionary relationships and distinguishability of that group of organisms. As further information comes to hand, the hypothesis may be corroborated or refuted. Sometimes, especially in the past when communication was more difficult, taxonomists working in isolation have given two distinct names to individual organisms later identified as

2205-400: A perfect model of life, it is still a useful tool to scientists and conservationists for studying life on Earth, regardless of the theoretical difficulties. If species were fixed and clearly distinct from one another, there would be no problem, but evolutionary processes cause species to change. This obliges taxonomists to decide, for example, when enough change has occurred to declare that

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2310-441: A phylogenetic tree. A cladogram only represents a branching pattern; i.e., its branch lengths do not represent time or relative amount of character change, and its internal nodes do not represent ancestors. A phylogram is a phylogenetic tree that has branch lengths proportional to the amount of character change. A chronogram is a phylogenetic tree that explicitly represents time through its branch lengths. A Dahlgrenogram

2415-400: A short way of saying that something applies to many species within a genus, but not to all. If scientists mean that something applies to all species within a genus, they use the genus name without the specific name or epithet. The names of genera and species are usually printed in italics . However, abbreviations such as "sp." should not be italicised. When a species' identity is not clear,

2520-404: A specialist may use "cf." before the epithet to indicate that confirmation is required. The abbreviations "nr." (near) or "aff." (affine) may be used when the identity is unclear but when the species appears to be similar to the species mentioned after. With the rise of online databases, codes have been devised to provide identifiers for species that are already defined, including: The naming of

2625-523: A species as groups of actually or potentially interbreeding natural populations, which are reproductively isolated from other such groups. It has been argued that this definition is a natural consequence of the effect of sexual reproduction on the dynamics of natural selection. Mayr's use of the adjective "potentially" has been a point of debate; some interpretations exclude unusual or artificial matings that occur only in captivity, or that involve animals capable of mating but that do not normally do so in

2730-400: A species as determined by a taxonomist. A typological species is a group of organisms in which individuals conform to certain fixed properties (a type), so that even pre-literate people often recognise the same taxon as do modern taxonomists. The clusters of variations or phenotypes within specimens (such as longer or shorter tails) would differentiate the species. This method was used as

2835-488: A species. All species definitions assume that an organism acquires its genes from one or two parents very like the "daughter" organism, but that is not what happens in HGT. There is strong evidence of HGT between very dissimilar groups of prokaryotes , and at least occasionally between dissimilar groups of eukaryotes , including some crustaceans and echinoderms . The evolutionary biologist James Mallet concludes that there

2940-685: A species. Generally the term includes the unknown element of a distinct act of creation. Many authors have argued that a simple textbook definition, following Mayr's concept, works well for most multi-celled organisms , but breaks down in several situations: Species identification is made difficult by discordance between molecular and morphological investigations; these can be categorised as two types: (i) one morphology, multiple lineages (e.g. morphological convergence , cryptic species ) and (ii) one lineage, multiple morphologies (e.g. phenotypic plasticity , multiple life-cycle stages). In addition, horizontal gene transfer (HGT) makes it difficult to define

3045-519: A taxonomic decision at the discretion of cognizant specialists, is not governed by the Codes of Zoological or Botanical Nomenclature, in contrast to the PhyloCode , and contrary to what is done in several other fields, in which the definitions of technical terms, like geochronological units and geopolitical entities, are explicitly delimited. The nomenclatural codes that guide the naming of species, including

3150-506: A traditional biological species. The International Committee on Taxonomy of Viruses has since 1962 developed a universal taxonomic scheme for viruses; this has stabilised viral taxonomy. Most modern textbooks make use of Ernst Mayr 's 1942 definition, known as the Biological Species Concept as a basis for further discussion on the definition of species. It is also called a reproductive or isolation concept. This defines

3255-445: A tree shape, defines a topology only. Some sequence-based trees built from a small genomic locus, such as Phylotree, feature internal nodes labeled with inferred ancestral haplotypes. The number of possible trees for a given number of leaf nodes depends on the specific type of tree, but there are always more labeled than unlabeled trees, more multifurcating than bifurcating trees, and more rooted than unrooted trees. The last distinction

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3360-447: A variation on the morphological species concept, a phenetic species, defined as a set of organisms with a similar phenotype to each other, but a different phenotype from other sets of organisms. It differs from the morphological species concept in including a numerical measure of distance or similarity to cluster entities based on multivariate comparisons of a reasonably large number of phenotypic traits. A mate-recognition species

3465-515: A variety of reasons. Viruses are a special case, driven by a balance of mutation and selection , and can be treated as quasispecies . Biologists and taxonomists have made many attempts to define species, beginning from morphology and moving towards genetics . Early taxonomists such as Linnaeus had no option but to describe what they saw: this was later formalised as the typological or morphological species concept. Ernst Mayr emphasised reproductive isolation, but this, like other species concepts,

3570-438: Is "an entity composed of organisms which maintains its identity from other such entities through time and over space, and which has its own independent evolutionary fate and historical tendencies". This differs from the biological species concept in embodying persistence over time. Wiley and Mayden stated that they see the evolutionary species concept as "identical" to Willi Hennig 's species-as-lineages concept, and asserted that

3675-604: Is a diagram representing a cross section of a phylogenetic tree. A phylogenetic network is not strictly speaking a tree, but rather a more general graph , or a directed acyclic graph in the case of rooted networks. They are used to overcome some of the limitations inherent to trees. A spindle diagram, or bubble diagram, is often called a romerogram, after its popularisation by the American palaeontologist Alfred Romer . It represents taxonomic diversity (horizontal width) against geological time (vertical axis) in order to reflect

3780-400: Is a group of sexually reproducing organisms that recognise one another as potential mates. Expanding on this to allow for post-mating isolation, a cohesion species is the most inclusive population of individuals having the potential for phenotypic cohesion through intrinsic cohesion mechanisms; no matter whether populations can hybridise successfully, they are still distinct cohesion species if

3885-452: Is a population of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring , typically by sexual reproduction . It is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity . Other ways of defining species include their karyotype , DNA sequence, morphology , behaviour, or ecological niche . In addition, paleontologists use

3990-458: Is a set of organisms adapted to a particular set of resources, called a niche, in the environment. According to this concept, populations form the discrete phenetic clusters that we recognise as species because the ecological and evolutionary processes controlling how resources are divided up tend to produce those clusters. A genetic species as defined by Robert Baker and Robert Bradley is a set of genetically isolated interbreeding populations. This

4095-414: Is called speciation . Charles Darwin was the first to describe the role of natural selection in speciation in his 1859 book The Origin of Species . Speciation depends on a measure of reproductive isolation , a reduced gene flow. This occurs most easily in allopatric speciation, where populations are separated geographically and can diverge gradually as mutations accumulate. Reproductive isolation

4200-412: Is called the specific name or the specific epithet (in botanical nomenclature , also sometimes in zoological nomenclature ). For example, Boa constrictor is one of the species of the genus Boa , with constrictor being the species' epithet. While the definitions given above may seem adequate at first glance, when looked at more closely they represent problematic species concepts. For example,

4305-403: Is described formally, in a publication that assigns it a unique scientific name. The description typically provides means for identifying the new species, which may not be based solely on morphology (see cryptic species ), differentiating it from other previously described and related or confusable species and provides a validly published name (in botany) or an available name (in zoology) when

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4410-671: Is further weakened by the existence of microspecies , groups of organisms, including many plants, with very little genetic variability, usually forming species aggregates . For example, the dandelion Taraxacum officinale and the blackberry Rubus fruticosus are aggregates with many microspecies—perhaps 400 in the case of the blackberry and over 200 in the dandelion, complicated by hybridisation , apomixis and polyploidy , making gene flow between populations difficult to determine, and their taxonomy debatable. Species complexes occur in insects such as Heliconius butterflies, vertebrates such as Hypsiboas treefrogs, and fungi such as

4515-726: Is hard or even impossible to test. Later biologists have tried to refine Mayr's definition with the recognition and cohesion concepts, among others. Many of the concepts are quite similar or overlap, so they are not easy to count: the biologist R. L. Mayden recorded about 24 concepts, and the philosopher of science John Wilkins counted 26. Wilkins further grouped the species concepts into seven basic kinds of concepts: (1) agamospecies for asexual organisms (2) biospecies for reproductively isolated sexual organisms (3) ecospecies based on ecological niches (4) evolutionary species based on lineage (5) genetic species based on gene pool (6) morphospecies based on form or phenotype and (7) taxonomic species,

4620-424: Is large as compared with other members of the genus Sitta , measuring 16.5 cm (6.5 in) in length. The folded wing measures 98–109 mm (3.9–4.3 in) in males and 97–100 mm (3.8–3.9 in) in females. The tail is 48–60 mm (1.9–2.4 in) in males and 52–56 mm (2.0–2.2 in) in females. The beak measures between 20 mm (0.79 in) and 24.9 mm (0.98 in) and

4725-506: Is most true of genetic material that is subject to lateral gene transfer and recombination , where different haplotype blocks can have different histories. In these types of analysis, the output tree of a phylogenetic analysis of a single gene is an estimate of the gene's phylogeny (i.e. a gene tree) and not the phylogeny of the taxa (i.e. species tree) from which these characters were sampled, though ideally, both should be very close. For this reason, serious phylogenetic studies generally use

4830-430: Is no sexual dimorphism . Juveniles are very similar to adults, but the streaks on the mantle are blue rather than white. The primary coverts of juveniles are also more closely lined with blue, and the underparts are paler overall, especially on the chest. Adults perform a complete moult after the breeding season, whereas juveniles only have a partial moult, in which they replace a variable number of rectrices . The bird

4935-403: Is no easy way to tell whether related geographic or temporal forms belong to the same or different species. Species gaps can be verified only locally and at a point of time. One is forced to admit that Darwin's insight is correct: any local reality or integrity of species is greatly reduced over large geographic ranges and time periods. The botanist Brent Mishler argued that the species concept

5040-468: Is not valid, notably because gene flux decreases gradually rather than in discrete steps, which hampers objective delimitation of species. Indeed, complex and unstable patterns of gene flux have been observed in cichlid teleosts of the East African Great Lakes . Wilkins argued that "if we were being true to evolution and the consequent phylogenetic approach to taxa, we should replace it with

5145-443: Is orange on the underparts. The crown and upper mantle are black, streaked with pale blue and white. The scapulars , back and rump are an azure blue. The greater and medium coverts are black, finely edged with white, forming two narrow wing bars ; the flight feathers are black and more or less lined with pale blue. The eyebrow and throat are white and buff and the eye is highlighted by an irregular, dark eyestripe. Under

5250-586: Is similar to Mayr's Biological Species Concept, but stresses genetic rather than reproductive isolation. In the 21st century, a genetic species could be established by comparing DNA sequences. Earlier, other methods were available, such as comparing karyotypes (sets of chromosomes ) and allozymes ( enzyme variants). An evolutionarily significant unit (ESU) or "wildlife species" is a population of organisms considered distinct for purposes of conservation. In palaeontology , with only comparative anatomy (morphology) and histology from fossils as evidence,

5355-421: Is sometimes an important source of genetic variation. Viruses can transfer genes between species. Bacteria can exchange plasmids with bacteria of other species, including some apparently distantly related ones in different phylogenetic domains , making analysis of their relationships difficult, and weakening the concept of a bacterial species. Phylogeny Phylogenetic trees may be rooted or unrooted. In

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5460-539: Is the most biologically relevant; it arises because there are many places on an unrooted tree to put the root. For bifurcating labeled trees, the total number of rooted trees is: For bifurcating labeled trees, the total number of unrooted trees is: Among labeled bifurcating trees, the number of unrooted trees with n {\displaystyle n} leaves is equal to the number of rooted trees with n − 1 {\displaystyle n-1} leaves. The number of rooted trees grows quickly as

5565-632: Is threatened by deforestation and the species appears to be in decline. It has been classified as vulnerable by the International Union for Conservation of Nature . The nuthatches constitute a genus – Sitta – of small passerine birds in the family Sittidae , typified by short, compressed wings and short, square 12-feathered tails , a compact body, longish pointed bills , strong toes with long claws, and behaviorally, by their unique head-first manner of descending tree trunks. Most nuthatches have gray or bluish upperparts and

5670-594: Is threatened by hybridisation, but this can be selected against once a pair of populations have incompatible alleles of the same gene, as described in the Bateson–Dobzhansky–Muller model . A different mechanism, phyletic speciation, involves one lineage gradually changing over time into a new and distinct form (a chronospecies ), without increasing the number of resultant species. Horizontal gene transfer between organisms of different species, either through hybridisation , antigenic shift , or reassortment ,

5775-727: Is uncertain but it is found further east in the north of Burma, in Chin State (in the Chin Hills–Arakan Yoma montane forests ), the Sagaing Region , in Kachin State and in Shan State . Data on the bird from Laos is erratic, but there are reports of sightings north of Phou Kobo, and of large numbers of the species wintering in the center of the country in the pristine wilderness of Nakai–Nam Theun . There are also reports of sightings in

5880-523: The ICZN for animals and the ICN for plants, do not make rules for defining the boundaries of the species. Research can change the boundaries, also known as circumscription, based on new evidence. Species may then need to be distinguished by the boundary definitions used, and in such cases the names may be qualified with sensu stricto ("in the narrow sense") to denote usage in the exact meaning given by an author such as

5985-399: The fly agaric . Natural hybridisation presents a challenge to the concept of a reproductively isolated species, as fertile hybrids permit gene flow between two populations. For example, the carrion crow Corvus corone and the hooded crow Corvus cornix appear and are classified as separate species, yet they can hybridise where their geographical ranges overlap. A ring species is

6090-498: The jaguar ( Panthera onca ) of Latin America or the leopard ( Panthera pardus ) of Africa and Asia. In contrast, the scientific names of species are chosen to be unique and universal (except for some inter-code homonyms ); they are in two parts used together : the genus as in Puma , and the specific epithet as in concolor . A species is given a taxonomic name when a type specimen

6195-414: The maroon oriole ( Oriolus traillii ) and the white-browed scimitar babbler ( Pomatorhinus schisticeps ). S. formosa forages from about the middle to the apex of tall trees, exploring the trunks and epiphyte-covered branches ( lichens , mosses , orchids ), for small insects , but also prospect on outermost branches. In Laos, individuals were observed feeding while perched on the larger branches of

6300-521: The tarsus is 19–22 mm (0.75–0.87 in) in length. The weight is not known. S. formosa' s vocalizations are not well known, but its song is described as "low and sweet in tone". Its call is typical of nuthatches, and similar to that of the Eurasian nuthatch ( Sitta europaea ), but less strident. The beautiful nuthatch forages alone, in pairs or in small groups of four to five individuals, though an unusual gathering of 21 individuals

6405-522: The velvet-fronted nuthatch ( S. frontalis ), yellow-billed nuthatch ( S. solangiae ) and the sulphur-billed nuthatch ( S. oenochlamys ), but its distribution being focused in the eastern Himalayas, and the uniqueness of its plumage, argues against the assumption. According to the International Ornithological Congress and ornithologist Alan P. Peterson, no subspecies have been identified. In 2014, Eric Pasquet, et al. published

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6510-540: The western rock nuthatch ( S. neumayer ) and the eastern rock nuthatch ( S. tephronota ); species in the " europaea " group, including the Eurasian nuthatch ( S. europaea ), Siberian nuthatch ( S. arctica ), chestnut-vented nuthatch ( S. nagaensis ), Kashmir nuthatch ( S. cashmirensis ), Indian nuthatch ( S. castanea ), chestnut-bellied nuthatch ( S. cinnamoventris ) and the Burmese nuthatch ( S. neglecta ); as well as

6615-411: The white-tailed nuthatch ( S. himalayensis ), and therefore, the white-browed nuthatch ( S. victoriae ). These close relatives are generally all species that plaster the entrance to their nest with mud. Described by Erik Matthysen in his 1998 treatise The Nuthatches as a bird that "deserves its name", the beautiful nuthatch has highly distinctive plumage. Its upperparts are black and azure , and it

6720-406: The "cynical species concept", and arguing that far from being cynical, it usefully leads to an empirical taxonomy for any given group, based on taxonomists' experience. Other biologists have gone further and argued that we should abandon species entirely, and refer to the "Least Inclusive Taxonomic Units" (LITUs), a view that would be coherent with current evolutionary theory. The species concept

6825-622: The Origin of Species explained how species could arise by natural selection . That understanding was greatly extended in the 20th century through genetics and population ecology . Genetic variability arises from mutations and recombination , while organisms themselves are mobile, leading to geographical isolation and genetic drift with varying selection pressures . Genes can sometimes be exchanged between species by horizontal gene transfer ; new species can arise rapidly through hybridisation and polyploidy ; and species may become extinct for

6930-405: The abbreviation "sp." in the singular or "spp." (standing for species pluralis , Latin for "multiple species") in the plural in place of the specific name or epithet (e.g. Canis sp.). This commonly occurs when authors are confident that some individuals belong to a particular genus but are not sure to which exact species they belong, as is common in paleontology . Authors may also use "spp." as

7035-570: The amount of hybridisation is insufficient to completely mix their respective gene pools . A further development of the recognition concept is provided by the biosemiotic concept of species. In microbiology , genes can move freely even between distantly related bacteria, possibly extending to the whole bacterial domain. As a rule of thumb, microbiologists have assumed that members of Bacteria or Archaea with 16S ribosomal RNA gene sequences more similar than 97% to each other need to be checked by DNA–DNA hybridisation to decide if they belong to

7140-474: The biological species concept, "the several versions" of the phylogenetic species concept, and the idea that species are of the same kind as higher taxa are not suitable for biodiversity studies (with the intention of estimating the number of species accurately). They further suggested that the concept works for both asexual and sexually-reproducing species. A version of the concept is Kevin de Queiroz 's "General Lineage Concept of Species". An ecological species

7245-505: The biological species concept, a cladistic species does not rely on reproductive isolation – its criteria are independent of processes that are integral in other concepts. Therefore, it applies to asexual lineages. However, it does not always provide clear cut and intuitively satisfying boundaries between taxa, and may require multiple sources of evidence, such as more than one polymorphic locus, to give plausible results. An evolutionary species, suggested by George Gaylord Simpson in 1951,

7350-1091: The bird was found associated with the Fokienia evergreen. They usually live at altitudes of 950 m (3,120 ft) and up to nearly 2,300 m (7,500 ft) during the warm seasons but may make seasonal vertical migration. In India, for example, the species spends the summer between 1,500 m (4,900 ft) and 2,100 m (6,900 ft), but was observed during winter at just 335 m (1,099 ft) in Sikkim and in northeastern Arunachal Pradesh at 460 m (1,510 ft) and between 600 m (2,000 ft) and 800 m (2,600 ft). In Burma, they were observed at between 975 m (3,199 ft) and 1,830 m (6,000 ft), in China between 350 m (1,150 ft) and 1,975 m (6,480 ft), in Laos between 1,950 m (6,400 ft) and 2,000 m (6,600 ft) and in Thailand,

7455-480: The book Elementary Geology , by Edward Hitchcock (first edition: 1840). Charles Darwin featured a diagrammatic evolutionary "tree" in his 1859 book On the Origin of Species . Over a century later, evolutionary biologists still use tree diagrams to depict evolution because such diagrams effectively convey the concept that speciation occurs through the adaptive and semirandom splitting of lineages. The term phylogenetic , or phylogeny , derives from

7560-428: The boundaries between closely related species become unclear with hybridisation , in a species complex of hundreds of similar microspecies , and in a ring species . Also, among organisms that reproduce only asexually , the concept of a reproductive species breaks down, and each clone is potentially a microspecies. Although none of these are entirely satisfactory definitions, and while the concept of species may not be

7665-504: The center of Laos and northern Vietnam, Fokienia trees, which are a known beautiful nuthatch foraging source and nesting site, are harvested for their high commercial value. Research conducted in 2001 indicated a population comprising 2,500 to 10,000 adults, and between 3,500 and 15,000 total individuals; these numbers are in decline. The species has been classified as vulnerable by the International Union for Conservation of Nature (IUCN). Species A species ( pl. : species)

7770-433: The concept of a chronospecies can be applied. During anagenesis (evolution, not necessarily involving branching), some palaeontologists seek to identify a sequence of species, each one derived from the phyletically extinct one before through continuous, slow and more or less uniform change. In such a time sequence, some palaeontologists assess how much change is required for a morphologically distinct form to be considered

7875-416: The concept of the chronospecies since fossil reproduction cannot be examined. The most recent rigorous estimate for the total number of species of eukaryotes is between 8 and 8.7 million. About 14% of these had been described by 2011. All species (except viruses ) are given a two-part name , called a "binomial". The first part of a binomial is the genus to which the species belongs. The second part

7980-435: The evidence to support hypotheses about evolutionarily divergent lineages that have maintained their hereditary integrity through time and space. Molecular markers may be used to determine diagnostic genetic differences in the nuclear or mitochondrial DNA of various species. For example, in a study done on fungi , studying the nucleotide characters using cladistic species produced the most accurate results in recognising

8085-437: The head and lined with the same colors on the wing feathers . The underparts are orange, and the eyebrow and throat are ochre . An irregular, dark eyestripe highlights its eye. S. formosa ' s ecology is not fully described, but it is known to feed on small insects and larvae found on the trunks and epiphyte -covered branches of trees in its range. Reproduction takes place from April to May;

8190-726: The nest is placed in the hole of an oak , rhododendron , or other large tree. The nest is made of plant material and fur in which the bird typically lays four to six eggs. Although the species is found in most of the countries making up the mainland of Southeast Asia , it appears to be rare throughout its range, its population being highly localized where it is found. The bird nests predominantly in montane forest at an altitudinal range from 950 m (3,120 ft) up to nearly 2,300 m (7,500 ft), with some seasonal height adjustment, down to around 300 m (980 ft) in winter. Its apparent localization within its range makes rigorous estimates of its population difficult, but its habitat

8295-905: The northwest of Vietnam and in central Laos. Its range stretches west into the northeast of India, where it was reported seen near Darjeeling in West Bengal , but not since 1933. It is present in Bhutan, and in the Indian states of Sikkim (in the town of Rangpo ), in Meghalaya (in the Khasi Hills ), in Assam (in the Dima Hasao district ), in the south of Arunachal Pradesh , and in Manipur and Nagaland . Its presence in Bangladesh

8400-478: The numerous fungi species of all the concepts studied. Versions of the phylogenetic species concept that emphasise monophyly or diagnosability may lead to splitting of existing species, for example in Bovidae , by recognising old subspecies as species, despite the fact that there are no reproductive barriers, and populations may intergrade morphologically. Others have called this approach taxonomic inflation , diluting

8505-540: The only observation of the species was at a height of 2,290 m (7,510 ft). The beautiful nuthatch has always been rare and very localized throughout its distribution, perhaps due to very specific ecological requirements, though this has been questioned as not in keeping with the diversity of habitats in which S. formosa has been observed. Although the species is less threatened at high elevations, its habitat has been reduced by deforestation , due to logging and forest clearance to make way for human habitation. In

8610-472: The opening of the hole is too large, it is cemented with mud to reduce the entrance size. The bird usually lays four to six white eggs, speckled with red spots, that measure 20.8 mm × 15.3 mm (0.82 in × 0.60 in). Beautiful nuthatch sexes are reported to share equally in nest building and incubation duties. This species lives in the eastern Himalayas , and has been reported in several scattered sites across Southeast Asia , in

8715-439: The optimal tree using many of these techniques is NP-hard , so heuristic search and optimization methods are used in combination with tree-scoring functions to identify a reasonably good tree that fits the data. Tree-building methods can be assessed on the basis of several criteria: Tree-building techniques have also gained the attention of mathematicians. Trees can also be built using T-theory . Trees can be encoded in

8820-585: The paper is accepted for publication. The type material is usually held in a permanent repository, often the research collection of a major museum or university, that allows independent verification and the means to compare specimens. Describers of new species are asked to choose names that, in the words of the International Code of Zoological Nomenclature , are "appropriate, compact, euphonious, memorable, and do not cause offence". Books and articles sometimes intentionally do not identify species fully, using

8925-403: The parent of all other nodes in the tree. The root is therefore a node of degree 2, while other internal nodes have a minimum degree of 3 (where "degree" here refers to the total number of incoming and outgoing edges). The most common method for rooting trees is the use of an uncontroversial outgroup —close enough to allow inference from trait data or molecular sequencing, but far enough to be

9030-674: The person who named the species, while the antonym sensu lato ("in the broad sense") denotes a wider usage, for instance including other subspecies. Other abbreviations such as "auct." ("author"), and qualifiers such as "non" ("not") may be used to further clarify the sense in which the specified authors delineated or described the species. Species are subject to change, whether by evolving into new species, exchanging genes with other species, merging with other species or by becoming extinct. The evolutionary process by which biological populations of sexually-reproducing organisms evolve to become distinct or reproductively isolated as species

9135-405: The range of DNA considered useful. Phylogenetic trees can also be inferred from a range of other data types, including morphology, the presence or absence of particular types of genes, insertion and deletion events – and any other observation thought to contain an evolutionary signal. Phylogenetic networks are used when bifurcating trees are not suitable, due to these complications which suggest

9240-473: The relatedness of the leaf nodes and do not require the ancestral root to be known or inferred. The idea of a tree of life arose from ancient notions of a ladder-like progression from lower into higher forms of life (such as in the Great Chain of Being ). Early representations of "branching" phylogenetic trees include a "paleontological chart" showing the geological relationships among plants and animals in

9345-487: The result of misclassification leading to questions on whether there really are any ring species. The commonly used names for kinds of organisms are often ambiguous: "cat" could mean the domestic cat, Felis catus , or the cat family, Felidae . Another problem with common names is that they often vary from place to place, so that puma, cougar, catamount, panther, painter and mountain lion all mean Puma concolor in various parts of America, while "panther" may also mean

9450-573: The ring. Ring species thus present a difficulty for any species concept that relies on reproductive isolation. However, ring species are at best rare. Proposed examples include the herring gull – lesser black-backed gull complex around the North pole, the Ensatina eschscholtzii group of 19 populations of salamanders in America, and the greenish warbler in Asia, but many so-called ring species have turned out to be

9555-574: The root of an unrooted tree requires some means of identifying ancestry. This is normally done by including an outgroup in the input data so that the root is necessarily between the outgroup and the rest of the taxa in the tree, or by introducing additional assumptions about the relative rates of evolution on each branch, such as an application of the molecular clock hypothesis . Both rooted and unrooted trees can be either bifurcating or multifurcating. A rooted bifurcating tree has exactly two descendants arising from each interior node (that is, it forms

9660-508: The same species. This concept was narrowed in 2006 to a similarity of 98.7%. The average nucleotide identity (ANI) method quantifies genetic distance between entire genomes , using regions of about 10,000 base pairs . With enough data from genomes of one genus, algorithms can be used to categorize species, as for Pseudomonas avellanae in 2013, and for all sequenced bacteria and archaea since 2020. Observed ANI values among sequences appear to have an "ANI gap" at 85–95%, suggesting that

9765-529: The same species. When two species names are discovered to apply to the same species, the older species name is given priority and usually retained, and the newer name considered as a junior synonym, a process called synonymy . Dividing a taxon into multiple, often new, taxa is called splitting . Taxonomists are often referred to as "lumpers" or "splitters" by their colleagues, depending on their personal approach to recognising differences or commonalities between organisms. The circumscription of taxa, considered

9870-417: The simpler algorithms (i.e. those based on distance) of tree construction. Maximum parsimony is another simple method of estimating phylogenetic trees, but implies an implicit model of evolution (i.e. parsimony). More advanced methods use the optimality criterion of maximum likelihood , often within a Bayesian framework , and apply an explicit model of evolution to phylogenetic tree estimation. Identifying

9975-431: The southeast of China’s Yunnan province, in northern Thailand and in northwestern Vietnam. Its residential and breeding range is estimated to cover 376,000 km (145,000 sq mi). Beautiful nuthatches typically inhabit both the interior and outskirts of evergreen or semi-evergreen montane forest , though in northern Burma they have been recorded nesting in trees scattered across open areas. In central Laos,

10080-502: The species concept and making taxonomy unstable. Yet others defend this approach, considering "taxonomic inflation" pejorative and labelling the opposing view as "taxonomic conservatism"; claiming it is politically expedient to split species and recognise smaller populations at the species level, because this means they can more easily be included as endangered in the IUCN red list and can attract conservation legislation and funding. Unlike

10185-399: The species has not been well studied. In the northeast of India, the breeding season is from April to May. The nest is placed off the ground, between two and eight meters high, and is often built in a hole of a (living or dead) oak or rhododendron tree, or sometimes in other large trees. Nests are constructed using leaves and bark, held together with hair, often that of bamboo rats . If

10290-456: The species is therefore sometimes called Callisitta Formosa . The beautiful nuthatch was first described in 1843 by British zoologist Edward Blyth , from a specimen he examined in Darjeeling . Its kinship with other members of the genus is unclear. The bright blue color of its plumage invites a comparison to the blue nuthatch ( S. azurea ), or other blue-tinted nuthatch species such as

10395-411: The tree before hybridisation takes place, and conserved sequences . Also, there are problems in basing an analysis on a single type of character, such as a single gene or protein or only on morphological analysis, because such trees constructed from another unrelated data source often differ from the first, and therefore great care is needed in inferring phylogenetic relationships among species. This

10500-529: The trees that they generate are not necessarily correct – they do not necessarily accurately represent the evolutionary history of the included taxa. As with any scientific result, they are subject to falsification by further study (e.g., gathering of additional data, analyzing the existing data with improved methods). The data on which they are based may be noisy ; the analysis can be confounded by genetic recombination , horizontal gene transfer , hybridisation between species that were not nearest neighbors on

10605-422: The two ancient greek words φῦλον ( phûlon ), meaning "race, lineage", and γένεσις ( génesis ), meaning "origin, source". A rooted phylogenetic tree (see two graphics at top) is a directed tree with a unique node — the root — corresponding to the (usually imputed ) most recent common ancestor of all the entities at the leaves of the tree. The root node does not have a parent node, but serves as

10710-404: The variation of abundance of various taxa through time. A spindle diagram is not an evolutionary tree: the taxonomic spindles obscure the actual relationships of the parent taxon to the daughter taxon and have the disadvantage of involving the paraphyly of the parental group. This type of diagram is no longer used in the form originally proposed. Darwin also mentioned that the coral may be

10815-537: The wild. It is difficult to define a species in a way that applies to all organisms. The debate about species concepts is called the species problem. The problem was recognised even in 1859, when Darwin wrote in On the Origin of Species : I was much struck how entirely vague and arbitrary is the distinction between species and varieties. He went on to write: No one definition has satisfied all naturalists; yet every naturalist knows vaguely what he means when he speaks of

10920-424: The wing, the white base of the primary coverts contrasts sharply with gray undertail-coverts ; a distinguishing trait when viewing the bird in flight. The iris is reddish-brown or dark brown and the bill is black but for a whitish tinge at the base of the lower mandible . The lower parts are generally orange-cinnamon. The legs and feet are yellowish-brown, olive-brown or greenish-brown. There

11025-493: Was observed in one tree in Bhutan. It often takes part in mixed-species foraging flocks , and has been notably observed feeding with the Himalayan cutia ( Cutia nipalensis ) and the velvet-fronted nuthatch ( Sitta frontalis ) – two other species that prospect for food on tree trunks. Other foraging flock partners surveyed are the long-tailed broadbill ( Psarisomus dalhousiae ), the lesser racket-tailed drongo ( Dicrurus remifer ),

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