153-658: The mute swan ( Cygnus olor ) is a species of swan and a member of the waterfowl family Anatidae . It is native to much of Eurasia , and (as a rare winter visitor) the far north of Africa. It is an introduced species in North America, home to the largest populations outside of its native range, with additional smaller introductions in Australasia and southern Africa. The name "mute" derives from it being less vocal than other swan species. Measuring 125 to 160 cm (49 to 63 in) in length, this large swan
306-423: 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
459-672: A paleosub species that differed only in size from the living bird, is known from fossils found in Azerbaijan . A related paleospecies recorded from fossils and subfossils is the Giant swan, Cygnus falconeri , a flightless species that lived on the islands of Malta and Sicily during the Middle Pleistocene . Fossils of swan ancestors more distantly allied to the mute swan have been found in four U.S. states: California , Arizona , Idaho , and Oregon . The timeline runs from
612-400: 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
765-424: 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
918-406: A 200 to 240 cm (79 to 94 in) wingspan. Males are larger than females and have a larger knob on their bill. On average, this is the second largest waterfowl species after the trumpeter swan , although male mute swans can easily match or even exceed a male trumpeter in mass. Among standard measurements of the mute swan, the wing chord measures 53–62.3 cm (20.9–24.5 in), the tarsus
1071-428: 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
1224-401: A contact sound between birds in flight. Cygnets are especially vocal and communicate through a variety of whistling and chirping sounds when content, as well as a harsher chirping noise when distressed or lost. Mute swans can be very aggressive in defence of their nests and are highly protective of their mate and offspring. Most defensive acts from a mute swan begin with a loud hiss and, if this
1377-450: A copy of a gene responsible for leucism . Mute swans nest on large mounds that they build with waterside vegetation in shallow water on islands in the middle or at the very edge of a lake. They are monogamous and often reuse the same nest each year, restoring or rebuilding it as needed. Male and female swans share the care of the nest, and once the cygnets are fledged it is not uncommon to see whole families looking for food. They feed on
1530-432: 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
1683-467: A flying bird, although it has been questioned whether this heavyweight could still take flight. Mute swans can achieve speeds in flight of up to 88.5 km/h (55 mph), and during take off achieve speeds of around 48 km/h (30 mph) when running to gain lift . Young birds, called cygnets, are not the bright white of mature adults, and their bill is dull greyish-black, not orange, for the first year. The down may range from pure white to grey to buff, with grey/buff
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#17327823866361836-508: 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
1989-420: A given airspeed depends on the shape of the airfoil, especially the amount of camber (curvature such that the upper surface is more convex than the lower surface, as illustrated at right). Increasing the camber generally increases the maximum lift at a given airspeed. Cambered airfoils generate lift at zero angle of attack. When the chord line is horizontal, the trailing edge has a downward direction and since
2142-436: A lift force roughly proportional to the angle of attack. As the angle of attack increases, the lift reaches a maximum at some angle; increasing the angle of attack beyond this critical angle of attack causes the upper-surface flow to separate from the wing; there is less deflection downward so the airfoil generates less lift. The airfoil is said to be stalled . The maximum lift force that can be generated by an airfoil at
2295-465: 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
2448-487: A lost or dead mate or cygnet. Swans will go through a mourning process, and in the case of the loss of their mate, may either stay where their counterpart lived or fly off to join a flock. Should one of the pair die while there are cygnets present, the remaining parent will take up their partner's duties in raising the clutch. Mute swans lay from 4 to 10 eggs. The female broods for around 36 days, with cygnets normally hatching between May and July. The young swans do not achieve
2601-492: 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
2754-449: 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
2907-400: 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
3060-463: A point is reached where the boundary layer can no longer remain attached to the upper surface. When the boundary layer separates, it leaves a region of recirculating flow above the upper surface, as illustrated in the flow-visualization photo at right. This is known as the stall , or stalling . At angles of attack above the stall, lift is significantly reduced, though it does not drop to zero. The maximum lift that can be achieved before stall, in terms of
3213-485: A pressure difference, and that the speed difference then leads to a pressure difference, by Bernoulli's principle. This implied one-way causation is a misconception. The real relationship between pressure and flow speed is a mutual interaction . As explained below under a more comprehensive physical explanation , producing a lift force requires maintaining pressure differences in both the vertical and horizontal directions. The Bernoulli-only explanations do not explain how
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#17327823866363366-400: 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,
3519-659: A single pair on smaller lakes, though in a few locations where a large area of suitable feeding habitat is found, they can be colonial. The largest colonies have over 100 pairs, such as at the colony at Abbotsbury Swannery in southern England, and at the southern tip of Öland Island, Ottenby Preserve, in the coastal waters of the Baltic Sea , and can have nests spaced as little as 2 m (7 ft) apart. Non-mated juveniles up to 3–4 years old commonly form larger flocks, which can total several hundred birds, often at regular traditional sites. A notable flock of non-breeding birds
3672-404: 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
3825-523: 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
3978-400: 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
4131-491: 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
4284-685: 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
4437-417: A steady flow without viscosity, lower pressure means higher speed, and higher pressure means lower speed. Thus changes in flow direction and speed are directly caused by the non-uniform pressure. But this cause-and-effect relationship is not just one-way; it works in both directions simultaneously. The air's motion is affected by the pressure differences, but the existence of the pressure differences depends on
4590-412: A streamlined airfoil, and with somewhat higher drag. Most simplified explanations follow one of two basic approaches, based either on Newton's laws of motion or on Bernoulli's principle . An airfoil generates lift by exerting a downward force on the air as it flows past. According to Newton's third law , the air must exert an equal and opposite (upward) force on the airfoil, which is lift. As
4743-480: A study of population sizes in the lower Great Lakes from 1971 to 2000 found that mute swan numbers were increasing at an average rate of at least 10% per year, doubling the population every seven to eight years. Several studies have concluded that mute swans severely reduce the densities of submerged vegetation where they occur. In 2003, the U.S. Fish and Wildlife Service proposed to "minimize environmental damages attributed to Mute Swans" by reducing their numbers in
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4896-528: 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
5049-477: A threat to infirm ones (healthy adults can usually swim away from danger and nest defence is usually successful) and there are a few cases of healthy adults falling prey to the golden eagles . In Great Britain, there has been an increased rate of attacks on swans by out-of-control dogs, especially in parks where the birds are less territorial. This is considered criminal in British law, and the birds are placed under
5202-517: 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
5355-447: 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
5508-515: 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,
5661-421: A weight range of 9.2–14.3 kg (20–32 lb) while the slightly smaller females (known as pens ) averaged about 8.5 to 9.67 kg (18.7 to 21.3 lb), with a weight range of 7.6–10.6 kg (17–23 lb). While the top normal weight for a big cob is roughly 15 kg (33 lb), one unusually big Polish cob weighed almost 23 kg (51 lb) and this counts as the largest weight ever verified for
5814-439: A wide area, producing a pattern called a velocity field . When an airfoil produces lift, the flow ahead of the airfoil is deflected upward, the flow above and below the airfoil is deflected downward leaving the air far behind the airfoil in the same state as the oncoming flow far ahead. The flow above the upper surface is sped up, while the flow below the airfoil is slowed down. Together with the upward deflection of air in front and
5967-529: A wide range of vegetation, both submerged aquatic plants which they reach with their long necks, and by grazing on land. The food commonly includes agricultural crop plants such as oilseed rape and wheat , and feeding flocks in the winter may cause significant crop damage, often as much through trampling with their large webbed feet, as through direct consumption. It will also feed on small proportions of aquatic insects , fish and frogs . Unlike black swans , mute swans are usually strongly territorial with just
6120-401: A wing in a wind tunnel) or whether both are moving (e.g. a sailboat using the wind to move forward). Lift is the component of this force that is perpendicular to the oncoming flow direction. Lift is always accompanied by a drag force, which is the component of the surface force parallel to the flow direction. Lift is mostly associated with the wings of fixed-wing aircraft , although it
6273-438: 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
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6426-439: Is 10–11.8 cm (3.9–4.6 in) and the bill is 6.9–9 cm (2.7–3.5 in). The plumage is white, while the legs are dark grey. The beak of the mute swan is bright orange, with black around the nostrils and a black nail . The mute swan is one of the heaviest extant flying birds. In several studies from Great Britain, males (known as cobs ) were found to average from about 10.6 to 11.87 kg (23.4 to 26.2 lb), with
6579-400: 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
6732-407: Is a result of pressure differences and depends on angle of attack, airfoil shape, air density, and airspeed. Pressure is the normal force per unit area exerted by the air on itself and on surfaces that it touches. The lift force is transmitted through the pressure, which acts perpendicular to the surface of the airfoil. Thus, the net force manifests itself as pressure differences. The direction of
6885-458: 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
7038-640: Is a variant form of cycnus , borrowing from Greek κύκνος kyknos , a word of the same meaning. Despite its Eurasian origin, its closest relatives are the black swan of Australia and the black-necked swan of South America, not the other Northern Hemisphere swans of the genus Cygnus . The species is monotypic , with no living subspecies . Mute swan subfossils, 6,000 years old, have been found in post-glacial peat beds of East Anglia , Great Britain. They have been recorded from Ireland east to Portugal and Italy , and from France , 13,000 BP (Desbrosse and Mourer-Chauvire 1972–1973). Cygnus olor bergmanni ,
7191-439: Is because the assumption of equal transit time is wrong when applied to a body generating lift. There is no physical principle that requires equal transit time in all situations and experimental results confirm that for a body generating lift the transit times are not equal. In fact, the air moving past the top of an airfoil generating lift moves much faster than equal transit time predicts. The much higher flow speed over
7344-414: 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
7497-412: 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,
7650-403: 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
7803-503: Is difficult because the cause-and-effect relationships involved are subtle. A comprehensive explanation that captures all of the essential aspects is necessarily complex. There are also many simplified explanations , but all leave significant parts of the phenomenon unexplained, while some also have elements that are simply incorrect. An airfoil is a streamlined shape that is capable of generating significantly more lift than drag. A flat plate can generate lift, but not as much as
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#17327823866367956-696: Is found on the River Tweed estuary at Berwick-upon-Tweed in northeastern England, with a maximum count of 787 birds. A large population exists near the Swan Lifeline Station in Windsor and lives on the Thames in the shadow of Windsor Castle . Once the adults are mated they seek out their territories and often live close to ducks and gulls , which may take advantage of the swan's ability to reach deep water weeds, which tend to spread out on
8109-671: 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
8262-726: 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,
8415-401: Is more widely generated by many other streamlined bodies such as propellers , kites , helicopter rotors , racing car wings , maritime sails , wind turbines , and by sailboat keels , ship's rudders , and hydrofoils in water. Lift is also used by flying and gliding animals , especially by birds , bats , and insects , and even in the plant world by the seeds of certain trees. While
8568-619: Is negligible. The lift force frequency is characterised by the dimensionless Strouhal number , which depends on the Reynolds number of the flow. For a flexible structure, this oscillatory lift force may induce vortex-induced vibrations. Under certain conditions – for instance resonance or strong spanwise correlation of the lift force – the resulting motion of the structure due to the lift fluctuations may be strongly enhanced. Such vibrations may pose problems and threaten collapse in tall man-made structures like industrial chimneys . In
8721-403: 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
8874-473: Is not sufficient to drive off the predator or intruder, are followed by a physical attack. Swans attack by striking at the threat with bony spurs in their wings, accompanied by biting with their large bill, while smaller waterbirds such as ducks are normally grabbed with the swan's bill and dragged or thrown clear of the swan and its offspring. Swans will kill intruders into their territory, both other swans, and geese and ducks, by drowning, climbing onto and pecking
9027-478: 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
9180-514: Is now allowed to be killed or held in captivity at the discretion of the Minister of Conservation . A small feral population exists in the vicinity of Perth , Australia ; however, it is believed to number less than 100 individuals. The mute swan has been the national bird of Denmark since 1984. Before that, the skylark was considered Denmark's national bird (since 1960). The fairy tale " The Ugly Duckling " by Hans Christian Andersen tells
9333-404: Is proportional to the density of the air and approximately proportional to the square of the flow speed. Lift also depends on the size of the wing, being generally proportional to the wing's area projected in the lift direction. In calculations it is convenient to quantify lift in terms of a lift coefficient based on these factors. No matter how smooth the surface of an airfoil seems, any surface
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#17327823866369486-529: Is responsible for defending the cygnets while on the water, and will sometimes attack small watercraft, such as canoes , that it feels are a threat to its young. The cob will additionally try to chase the predator out of his family territory and will keep animals such as foxes and raptors at bay. In New York (outside its native range), the most common predators of cygnets are common snapping turtles . Healthy adults are rarely preyed upon, though canids such as coyotes , felids such as lynx , and bears can pose
9639-409: Is rough on the scale of air molecules. Air molecules flying into the surface bounce off the rough surface in random directions relative to their original velocities. The result is that when the air is viewed as a continuous material, it is seen to be unable to slide along the surface, and the air's velocity relative to the airfoil decreases to nearly zero at the surface (i.e., the air molecules "stick" to
9792-732: Is shared with the Vintners' and Dyers' Companies, who were granted rights of ownership by the Crown in the 15th century. The mute swans in the moat at the Bishops Palace at Wells Cathedral in Wells , England have for centuries been trained to ring bells via strings attached to them to beg for food. Two swans are still able to ring for lunch. The pair of swans in the Boston Public Garden are named Romeo and Juliet after
9945-586: 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,
10098-414: 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. Lift (force) When a fluid flows around an object,
10251-594: 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 ,
10404-428: Is tilted with respect to the vertical. Lift may also act as downforce on the wing of a fixed-wing aircraft at the top of an aerobatic loop , and on the horizontal stabiliser of an aircraft. Lift may also be largely horizontal, for instance on a sailing ship. The lift discussed in this article is mainly in relation to airfoils, although marine hydrofoils and propellers share the same physical principles and work in
10557-512: Is wholly white in plumage with an orange beak bordered with black. It is recognisable by its pronounced knob atop the beak, which is larger in males. The mute swan was first formally named by the German naturalist Johann Friedrich Gmelin as Anas olor in 1789 and was transferred by Johann Matthäus Bechstein to the new genus Cygnus in 1803. Both cygnus and olor mean "swan" in Latin ; cygnus
10710-601: The Atlantic Flyway to pre-1986 levels, a 67% reduction at the time. According to a report published in the Federal Register of 2003 the proposal was supported by all thirteen state wildlife agencies which submitted comments, as well as by 43 bird conservation, wildlife conservation and wildlife management organisations. Ten animal rights organisations and the vast majority of comments from individuals were opposed. At this time mute swans were protected under
10863-530: 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
11016-629: The Magnus effect , a lift force is generated by a spinning cylinder in a freestream. Here the mechanical rotation acts on the boundary layer, causing it to separate at different locations on the two sides of the cylinder. The asymmetric separation changes the effective shape of the cylinder as far as the flow is concerned such that the cylinder acts like a lifting airfoil with circulation in the outer flow. As described above under " Simplified physical explanations of lift on an airfoil ", there are two main popular explanations: one based on downward deflection of
11169-770: The Migratory Bird Treaty Act due to a court order, but in 2005 the United States Department of the Interior officially declared them a non-native, unprotected species. Mute swans are protected in some areas of the U.S. by local laws, for example, in Connecticut . The status of the mute swan as an introduced species in North America is disputed by the interest group "Save the Mute Swans". They assert that mute swans are native to
11322-873: The Miocene to the late Pleistocene or 10,000 BP. The latest find was in Anza-Borrego Desert, a state park in California. Fossils from the Pleistocene include Cygnus paloregonus from Fossil Lake, Oregon, Froman's Ferry, Idaho, and Arizona, referred to by Howard in The Waterfowl of the World as "probably the mute type swan". Adults of this large swan typically range from 140 to 160 cm (55 to 63 in) long, although can range in extreme cases from 125 to 170 cm (49 to 67 in), with
11475-691: The Shakespearean couple ; however, it was found that both of them are females. While The Sydney Swans Football Club earned their nickname from the many players they recruited from Western Australia in the 1930's (the Black Swan being the State's Badge and Bird ), the Football Club adopted the Mute Swan as their symbol as it matched their red and white team colours. The swan's plumage on
11628-399: 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
11781-507: 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
11934-446: The streamline curvature theorem , was derived from Newton's second law by Leonhard Euler in 1754: The left side of this equation represents the pressure difference perpendicular to the fluid flow. On the right side of the equation, ρ is the density, v is the velocity, and R is the radius of curvature. This formula shows that higher velocities and tighter curvatures create larger pressure differentials and that for straight flow (R → ∞),
12087-549: The "Coandă effect" is applicable, calling it the "Coandă effect" does not provide an explanation, it just gives the phenomenon a name. The ability of a fluid flow to follow a curved path is not dependent on shear forces, viscosity of the fluid, or the presence of a boundary layer. Air flowing around an airfoil, adhering to both upper and lower surfaces, and generating lift, is accepted as a phenomenon in inviscid flow. There are two common versions of this explanation, one based on "equal transit time", and one based on "obstruction" of
12240-406: 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
12393-1063: The 2006–2007 winter, a slight decline from the peak of about 26,000–27,000 birds in 1990. This includes about 5,300 breeding pairs, the remainder being immatures. Other significant populations in Europe include 6,800–8,300 breeding pairs in Germany , 4,500 pairs in Denmark , 4,000–4,200 pairs in Poland , 3,000–4,000 pairs in the Netherlands , about 2,500 pairs in Ireland , and 1,200–1,700 pairs in Ukraine . For many centuries, mute swans in Great Britain were domesticated for food, with individuals being marked by nicks on their webs (feet) or beaks to indicate ownership. These marks were registered with
12546-510: The Crown and a Royal Swanherd was appointed. Any birds not so marked became Crown property, hence the swan becoming known as the "Royal Bird". This domestication saved the mute swan from extirpation through overhunting in Great Britain. Populations in Western Europe were largely exterminated by hunting pressure in the 13th–19th centuries, except for semi-domesticated birds maintained as poultry by large landowners. Better protection in
12699-753: The Mediterranean. It is known and recorded to have nested in Iceland and is a vagrant in that area as well as in Bermuda, according to the UN Environment Programme chart of international status chart of bird species, which places it in 70 countries, breeding in 49 countries, and vagrant in 16 countries. While most of the current population in Japan is introduced, mute swans are depicted on scrolls more than 1,000 years old, and wild birds from
12852-626: 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
13005-405: 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
13158-524: The ability to fly before about 120 to 150 days old. This limits the distribution of the species at the northern edge of its range as the cygnets need to learn to fly before the ponds and lakes freeze over. The mute swan is found naturally mainly in temperate areas of Europe, then across the Palearctic as far east as Primorsky Krai , near Sidemi. It is partially migratory throughout northern latitudes in Europe and Asia, as far south as North Africa and
13311-439: The air follows the trailing edge it is deflected downward. When a cambered airfoil is upside down, the angle of attack can be adjusted so that the lift force is upward. This explains how a plane can fly upside down. The ambient flow conditions which affect lift include the fluid density, viscosity and speed of flow. Density is affected by temperature, and by the medium's acoustic velocity – i.e. by compressibility effects. Lift
13464-418: The air's motion. The relationship is thus a mutual, or reciprocal, interaction: Air flow changes speed or direction in response to pressure differences, and the pressure differences are sustained by the air's resistance to changing speed or direction. A pressure difference can exist only if something is there for it to push against. In aerodynamic flow, the pressure difference pushes against the air's inertia, as
13617-411: The airflow approaches the airfoil it is curving upward, but as it passes the airfoil it changes direction and follows a path that is curved downward. According to Newton's second law, this change in flow direction requires a downward force applied to the air by the airfoil. Then Newton's third law requires the air to exert an upward force on the airfoil; thus a reaction force, lift, is generated opposite to
13770-400: The airflow. The "equal transit time" explanation starts by arguing that the flow over the upper surface is faster than the flow over the lower surface because the path length over the upper surface is longer and must be traversed in equal transit time. Bernoulli's principle states that under certain conditions increased flow speed is associated with reduced pressure. It is concluded that
13923-490: The airfoil and behind also indicate that air passing through the low-pressure region above the airfoil is sped up as it enters, and slowed back down as it leaves. Air passing through the high-pressure region below the airfoil is slowed down as it enters and then sped back up as it leaves. Thus the non-uniform pressure is also the cause of the changes in flow speed visible in the flow animation. The changes in flow speed are consistent with Bernoulli's principle , which states that in
14076-462: The airfoil can impart downward turning to a much deeper swath of the flow than it actually touches. Furthermore, it does not mention that the lift force is exerted by pressure differences , and does not explain how those pressure differences are sustained. Some versions of the flow-deflection explanation of lift cite the Coandă effect as the reason the flow is able to follow the convex upper surface of
14229-408: The airfoil is pushed outward from the center of the high-pressure region. According to Newton's second law , a force causes air to accelerate in the direction of the force. Thus the vertical arrows in the accompanying pressure field diagram indicate that air above and below the airfoil is accelerated, or turned downward, and that the non-uniform pressure is thus the cause of the downward deflection of
14382-429: The airfoil's surfaces. Pressure in a fluid is always positive in an absolute sense, so that pressure must always be thought of as pushing, and never as pulling. The pressure thus pushes inward on the airfoil everywhere on both the upper and lower surfaces. The flowing air reacts to the presence of the wing by reducing the pressure on the wing's upper surface and increasing the pressure on the lower surface. The pressure on
14535-458: The airfoil. The conventional definition in the aerodynamics field is that the Coandă effect refers to the tendency of a fluid jet to stay attached to an adjacent surface that curves away from the flow, and the resultant entrainment of ambient air into the flow. More broadly, some consider the effect to include the tendency of any fluid boundary layer to adhere to a curved surface, not just
14688-501: The amount of constriction or obstruction do not predict experimental results. Another flaw is that conservation of mass is not a satisfying physical reason why the flow would speed up. Effectively explaining the acceleration of an object requires identifying the force that accelerates it. A serious flaw common to all the Bernoulli-based explanations is that they imply that a speed difference can arise from causes other than
14841-570: 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
14994-404: The back of the head and forcing the other bird underwater. The wings of the swan are very powerful, though not strong enough to break an adult man's leg, as is commonly misquoted. Large waterfowl, such as Canada geese (more likely out of competition than in response to potential predation), may be aggressively driven off, and mute swans regularly attack people who enter their territory. The cob
15147-474: 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
15300-505: 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,
15453-428: 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
15606-455: The boundary layer accompanying a fluid jet. It is in this broader sense that the Coandă effect is used by some popular references to explain why airflow remains attached to the top side of an airfoil. This is a controversial use of the term "Coandă effect"; the flow following the upper surface simply reflects an absence of boundary-layer separation, thus it is not an example of the Coandă effect. Regardless of whether this broader definition of
15759-459: The busking posture for wind-assisted transportation over several hundred meters, so-called windsurfing. When very young, cygnets may climb onto the back of one of their parents if they become tired while on the water, with the adult proceeding to carry them around. Cygnets may also shelter beneath their parent's wings during periods of heavy rain as a means to stay warm and dry. Like other swans, mute swans are known for their ability to grieve for
15912-400: The common meaning of the word " lift " assumes that lift opposes weight, lift can be in any direction with respect to gravity, since it is defined with respect to the direction of flow rather than to the direction of gravity. When an aircraft is cruising in straight and level flight, the lift opposes gravity. However, when an aircraft is climbing , descending , or banking in a turn the lift
16065-433: 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
16218-416: 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
16371-415: The directional change. In the case of an airplane wing, the wing exerts a downward force on the air and the air exerts an upward force on the wing. The downward turning of the flow is not produced solely by the lower surface of the airfoil, and the air flow above the airfoil accounts for much of the downward-turning action. This explanation is correct but it is incomplete. It does not explain how
16524-421: The downward deflection of the air immediately behind, this establishes a net circulatory component of the flow. The downward deflection and the changes in flow speed are pronounced and extend over a wide area, as can be seen in the flow animation on the right. These differences in the direction and speed of the flow are greatest close to the airfoil and decrease gradually far above and below. All of these features of
16677-422: The downward turning, but this is false. (see above under " Controversy regarding the Coandă effect "). The arrows ahead of the airfoil indicate that the flow ahead of the airfoil is deflected upward, and the arrows behind the airfoil indicate that the flow behind is deflected upward again, after being deflected downward over the airfoil. These deflections are also visible in the flow animation. The arrows ahead of
16830-628: The eastern United States and Great Lakes , much as the Canada goose has done in Europe. The total native population of mute swans is about 500,000 birds at the end of the breeding season (adults plus young), of which up to 350,000 are in Russia . The largest single breeding concentration is 11,000 pairs in the Volga Delta . The population in the United Kingdom is about 22,000 birds as of
16983-435: 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
17136-414: The flow (Newton's laws), and one based on pressure differences accompanied by changes in flow speed (Bernoulli's principle). Either of these, by itself, correctly identifies some aspects of the lifting flow but leaves other important aspects of the phenomenon unexplained. A more comprehensive explanation involves both downward deflection and pressure differences (including changes in flow speed associated with
17289-409: The flow visible in the flow animation. To produce this downward turning, the airfoil must have a positive angle of attack or have sufficient positive camber. Note that the downward turning of the flow over the upper surface is the result of the air being pushed downward by higher pressure above it than below it. Some explanations that refer to the "Coandă effect" suggest that viscosity plays a key role in
17442-428: The fluid exerts a force on the object. Lift is the component of this force that is perpendicular to the oncoming flow direction. It contrasts with the drag force, which is the component of the force parallel to the flow direction. Lift conventionally acts in an upward direction in order to counter the force of gravity , but it is defined to act perpendicular to the flow and therefore can act in any direction. If
17595-413: The head and neck) are often stained orange-brown by iron and tannins in the water. The colour morph C. o. morpha immutabilis ( immūtābilis is Latin for "immutable, unchangeable, unalterable"), also known as the "Polish swan", has pinkish (not dark grey) legs and dull white cygnets; as with white domestic geese , it is found only in populations with a history of domestication. Polish swans carry
17748-456: The highest protection due to their association with the monarch. Mute swans will readily attack dogs to protect themselves and their cygnets from an attack, and an adult swan is capable of overwhelming and drowning even large dog breeds. The familiar pose with the neck curved back and wings half raised, known as busking, is a threat display. Both feet are paddled in unison during this display, resulting in more jerky movement. The swans may also use
17901-607: The late 19th and early 20th centuries allowed the species to expand and return to most or all of their former range. More recently in the period from about 1960 up to the early 1980s, numbers declined significantly again in many areas in England, primarily due to lead poisoning from birds swallowing lead shots from shooting and discarded fishing weights made from lead . After lead weights and shots were mostly replaced by other less toxic alternatives, mute swan numbers increased again rapidly. Since being introduced into North America,
18054-410: The lift by a modest amount and modifies the pressure distribution somewhat, which results in a viscosity-related pressure drag over and above the skin friction drag. The total of the skin friction drag and the viscosity-related pressure drag is usually called the profile drag . An airfoil's maximum lift at a given airspeed is limited by boundary-layer separation . As the angle of attack is increased,
18207-421: The lift coefficient, is generally less than 1.5 for single-element airfoils and can be more than 3.0 for airfoils with high-lift slotted flaps and leading-edge devices deployed. The flow around bluff bodies – i.e. without a streamlined shape, or stalling airfoils – may also generate lift, in addition to a strong drag force. This lift may be steady, or it may oscillate due to vortex shedding . Interaction of
18360-644: The logo is designed to replicate the sails of the Sydney Opera House . Species A species ( pl. : species) 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
18513-400: The lower portion of the body is immersed in a liquid flow, is used by motorboats, surfboards, windsurfers, sailboats, and water-skis. A fluid flowing around the surface of a solid object applies a force on it. It does not matter whether the object is moving through a stationary fluid (e.g. an aircraft flying through the air) or whether the object is stationary and the fluid is moving (e.g.
18666-403: The lower surface pushes up harder than the reduced pressure on the upper surface pushes down, and the net result is upward lift. The pressure difference which results in lift acts directly on the airfoil surfaces; however, understanding how the pressure difference is produced requires understanding what the flow does over a wider area. An airfoil affects the speed and direction of the flow over
18819-436: The mainland Asian population still occur rarely in winter. Natural migrants to Japan usually occur along with whooper and sometimes Bewick's swans. The mute swan is protected in most of its range, but this has not prevented illegal hunting and poaching . It is often kept in captivity outside its natural range, as a decoration for parks and ponds, and escapes have happened. The descendants of such birds have become naturalised in
18972-419: The most common. The white cygnets have a leucistic gene. Cygnets grow quickly, reaching a size close to their adult size in approximately three months after hatching. Cygnets typically retain their grey feathers until they are at least one year old, with the down on their wings having been replaced by flight feathers earlier that year. All mute swans are white at maturity, though the feathers (particularly on
19125-651: The mute swan has increased greatly in number to the extent that it is considered an invasive species there. Populations introduced into other areas remain small, with around 200 in Japan, fewer than 200 in New Zealand and Australia , and about 120 in South Africa . The mute swan was introduced to North America in the late 19th century. Recently, it has been widely viewed as an invasive species because of its rapidly increasing numbers and its adverse effects on other waterfowl and native ecosystems . For example,
19278-494: The net force implies that the average pressure on the upper surface of the airfoil is lower than the average pressure on the underside. These pressure differences arise in conjunction with the curved airflow. When a fluid follows a curved path, there is a pressure gradient perpendicular to the flow direction with higher pressure on the outside of the curve and lower pressure on the inside. This direct relationship between curved streamlines and pressure differences, sometimes called
19431-483: 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
19584-413: The object's flexibility with the vortex shedding may enhance the effects of fluctuating lift and cause vortex-induced vibrations . For instance, the flow around a circular cylinder generates a Kármán vortex street : vortices being shed in an alternating fashion from the cylinder's sides. The oscillatory nature of the flow produces a fluctuating lift force on the cylinder, even though the net (mean) force
19737-593: 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
19890-674: 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
20043-422: The pressure difference is zero. The angle of attack is the angle between the chord line of an airfoil and the oncoming airflow. A symmetrical airfoil generates zero lift at zero angle of attack. But as the angle of attack increases, the air is deflected through a larger angle and the vertical component of the airstream velocity increases, resulting in more lift. For small angles, a symmetrical airfoil generates
20196-435: The pressure differences in the vertical direction are sustained. That is, they leave out the flow-deflection part of the interaction. Although the two simple Bernoulli-based explanations above are incorrect, there is nothing incorrect about Bernoulli's principle or the fact that the air goes faster on the top of the wing, and Bernoulli's principle can be used correctly as part of a more complicated explanation of lift. Lift
20349-405: The pressure differences), and requires looking at the flow in more detail. The airfoil shape and angle of attack work together so that the airfoil exerts a downward force on the air as it flows past. According to Newton's third law, the air must then exert an equal and opposite (upward) force on the airfoil, which is the lift. The net force exerted by the air occurs as a pressure difference over
20502-428: The reduced pressure over the upper surface results in upward lift. While it is true that the flow speeds up, a serious flaw in this explanation is that it does not correctly explain what causes the flow to speed up. The longer-path-length explanation is incorrect. No difference in path length is needed, and even when there is a difference, it is typically much too small to explain the observed speed difference. This
20655-579: The region and therefore deserving of protection. They claim that mute swans had origins in Russia and cite historical sightings and fossil records. These claims have been rejected as specious by the U.S. Department of the Interior. The mute swan had absolute protection in New Zealand under the Wildlife Act 1953 , but this was changed in June 2010 to a lower level of protection. It still has protection, but
20808-487: 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
20961-406: The rhythm of the song typically fails to match the pace of the head movements of two dating swans. Mute swans usually hiss at competitors or intruders trying to enter their territory. The most familiar sound associated with mute swans is the vibrant throbbing of the wings in flight which is unique to the species and can be heard from a range of 1 to 2 km (0.6 to 1 mi), indicating its value as
21114-586: 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
21267-508: 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
21420-529: 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
21573-507: The same way, despite differences between air and water such as density, compressibility, and viscosity. The flow around a lifting airfoil is a fluid mechanics phenomenon that can be understood on essentially two levels: There are mathematical theories , which are based on established laws of physics and represent the flow accurately, but which require solving equations. And there are physical explanations without math, which are less rigorous. Correctly explaining lift in these qualitative terms
21726-506: 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
21879-572: The story of a cygnet ostracised by his fellow barnyard fowl because of his perceived unattractiveness. To his delight (and to the surprise of others), he matures into a graceful swan, the most beautiful bird of all. Today, the British Monarch retains the right to ownership of all unmarked mute swans in open water, but King Charles III exercises his ownership only on certain stretches of the Thames and its surrounding tributaries. This ownership
22032-406: The streamlines to pinch closer together, making the streamtubes narrower. When streamtubes become narrower, conservation of mass requires that flow speed must increase. Reduced upper-surface pressure and upward lift follow from the higher speed by Bernoulli's principle , just as in the equal transit time explanation. Sometimes an analogy is made to a venturi nozzle , claiming the upper surface of
22185-432: The surface instead of sliding along it), something known as the no-slip condition . Because the air at the surface has near-zero velocity but the air away from the surface is moving, there is a thin boundary layer in which air close to the surface is subjected to a shearing motion. The air's viscosity resists the shearing, giving rise to a shear stress at the airfoil's surface called skin friction drag . Over most of
22338-416: The surface is just part of this pressure field. The non-uniform pressure exerts forces on the air in the direction from higher pressure to lower pressure. The direction of the force is different at different locations around the airfoil, as indicated by the block arrows in the pressure field around an airfoil figure. Air above the airfoil is pushed toward the center of the low-pressure region, and air below
22491-428: The surface of most airfoils, the boundary layer is naturally turbulent, which increases skin friction drag. Under usual flight conditions, the boundary layer remains attached to both the upper and lower surfaces all the way to the trailing edge, and its effect on the rest of the flow is modest. Compared to the predictions of inviscid flow theory, in which there is no boundary layer, the attached boundary layer reduces
22644-431: The surrounding fluid is air, the force is called an aerodynamic force . In water or any other liquid, it is called a hydrodynamic force . Dynamic lift is distinguished from other kinds of lift in fluids. Aerostatic lift or buoyancy , in which an internal fluid is lighter than the surrounding fluid, does not require movement and is used by balloons, blimps, dirigibles, boats, and submarines. Planing lift , in which only
22797-414: The upper surface can be clearly seen in this animated flow visualization . Like the equal transit time explanation, the "obstruction" or "streamtube pinching" explanation argues that the flow over the upper surface is faster than the flow over the lower surface, but gives a different reason for the difference in speed. It argues that the curved upper surface acts as more of an obstacle to the flow, forcing
22950-445: The velocity field also appear in theoretical models for lifting flows. The pressure is also affected over a wide area, in a pattern of non-uniform pressure called a pressure field . When an airfoil produces lift, there is a diffuse region of low pressure above the airfoil, and usually a diffuse region of high pressure below, as illustrated by the isobars (curves of constant pressure) in the drawing. The pressure difference that acts on
23103-426: The water surface. The mute swan is less vocal than the noisy whooper and tundra swans ; they do, however, make a variety of sounds, often described as "grunting, hoarse whistling, and snorting noises." During a courtship display, mute swans utter a rhythmic song. The song helps synchronize the movements of their heads and necks. It could technically be employed to distinguish a bonded couple from two dating swans, as
23256-540: 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
23409-525: The wing acts like a venturi nozzle to constrict the flow. One serious flaw in the obstruction explanation is that it does not explain how streamtube pinching comes about, or why it is greater over the upper surface than the lower surface. For conventional wings that are flat on the bottom and curved on top this makes some intuitive sense, but it does not explain how flat plates, symmetric airfoils, sailboat sails, or conventional airfoils flying upside down can generate lift, and attempts to calculate lift based on
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