title: Lipedema

text: The cause is unknown but is believed to involve genetics and hormonal factors. It often runs in families; having a family member with the condition is a risk factor for developing it. Other conditions that may present similarly include lipohypertrophy, chronic venous insufficiency, and lymphedema. It is estimated to affect up to 11% of women. Onset is typically during puberty, pregnancy, or menopause.


title: Lipedema

text: The fat associated with lipedema is shown to be resistant to weight loss methods; however, unlike other fat, lipedema is not associated with increased risks of diabetes or cardiovascular disease. Physiotherapy may help to preserve mobility for a little longer than would otherwise be the case. Exercise, only as much as the patient is able to do without causing damage to the joints, may help with overall fitness but will not prevent progression of the disease. Compression stockings can help with pain and make walking easier. Regularly moisturising with emollients protects the skin and prevents it from drying out. Liposuction to remove the fat can help if the symptoms are particularly severe. While surgery can remove fat tissue it can also damage lymphatic vessels. Treatment does not typically result in complete resolution.


title: Lipedema

text: Depression and anxiety are very common for a variety of reasons, particularly the fact that diagnosis usually takes a long time and patients have received much advice on diet and exercise in the meantime, neither of which are effective treatment for the lipedema although they may help associated conditions. Joint pain, arthritis, dry skin, fungal infections, cellulitis and slow wound healing are also associated with lipedema.


title: Lipedema

text: Stage 3: Bulky extrusions of skin and fat cause large deformations especially on the thighs and around the knees. These large extrusions of tissue drastically inhibit mobility.


title: Lipedema

text: Lipedema is often underdiagnosed due to the difficulty in differentiating it from lymphedema, obesity, or other edemas.


title: Lipedema

text: Lipo-lymphedema, a secondary lymphedema, is associated with both lipedema and obesity (which occur together in the majority of cases), most often lipedema stages 2 and 3.


title: Lipedema

text: Lipedema / Dercum's disease differentiation – these conditions may co-exist. Dercum's disease is a syndrome of painful growths in subcutaneous fat. Unlike lipedema, which occurs primarily in the trunk and legs, the fatty growths can occur anywhere on the body.


title: Lipedema

text: A number of treatments may be useful including physiotherapy and light exercise which does not put undue stress on the lymphatic system. The two most common conservative treatments are manual lymphatic drainage (MLD) where a therapist gently opens lymphatic channels and moves the lymphatic fluid using hands-on techniques, and compression garments that keep the fluid at bay and assist the sluggish lymphatic flow.


title: Lipedema

text: The use of surgical techniques is not universal but research has shown positive results in both short-term and long-term studies regarding lymph-sparing liposuction and lipectomy.


title: Lipedema

text: The studies of highest quality involve tumescent local anesthesia (TLA), often referred to as simply tumescent liposuction. This can be accomplished via both Suction-Assisted Liposuction (SAL) and Power-Assisted (vibrating) liposuction. The treatment of lipedema with tumescent liposuction may require multiple procedures. While many health insurance carriers in the United States do not reimburse for liposuction for lipedema, in 2020 several carriers regard the procedure as reconstructive and medically necessary and do reimburse. Water Assisted Liposuction (WAL) is technically not considered to be tumescent but achieves the same goal as the anesthetic solution is injected as part of the procedure rather than before-hand. Developed by Doctor Ziah Taufig from Germany, it is usually performed under general anesthesia and is also considered to be lymph-sparing and protective of other tissues such blood vessels.


title: Lipedema

text: There is no cure. Complications include a malformed appearance, reduced functionality (mobility and gait), poor quality of life (QOL), depression, anxiety, and pain.


title: Lipedema

text: According to an epidemiologic study by Földi E and Földi M, lipedema affects 11% of the female population, although rates from 6-39% have also been reported.


title: Lipedema

text: Lipedema was first identified in the United States, at the Mayo Clinic, in 1940. Most attribute the original identification of lipedema to E. A. Hines and L. E. Wold (1951). In spite of that, lipedema is barely known in the United States to physicians or to the patients who have the disease. Lipedema often is confused with obesity or lymphedema, and a significant number of patients currently diagnosed as obese are believed to have lipedema, either instead of or in addition to obesity.


title: Adult-onset Still's disease

text: Adult-onset Still's disease (AOSD) is a form of Still's disease, a rare systemic autoinflammatory disease characterized by the classic triad of fevers, joint pain, and a distinctive salmon-colored bumpy rash. The disease is considered a diagnosis of exclusion. Levels of the iron-binding protein ferritin may be extremely elevated with this disorder. AOSD may present in a similar manner to other inflammatory diseases and to autoimmune diseases, which must be ruled out before making the diagnosis.


title: Adult-onset Still's disease

text: Prognosis is usually favorable but manifestations of the disease affecting the lungs, heart, or kidneys may occasionally cause severe life-threatening complications. It is treated first with corticosteroids such as prednisone. Medications that block the action of interleukin-1, such as anakinra, can be effective treatments when standard steroid treatments are insufficient.


title: Adult-onset Still's disease

text: Obvious similarities exist with juvenile rheumatoid arthritis (also known as "juvenile-onset Still's disease"), and there is some evidence that the two conditions are closely related.


title: Adult-onset Still's disease

text: The disease typically presents with joint pain, high fevers, a salmon-pink macular or maculopapular rash, enlargement of the liver and spleen, swollen lymph nodes, and a neutrophil-predominant increased white blood cell count in the blood. Tests for rheumatoid factor and anti-nuclear antibodies are usually negative and serum ferritin is markedly elevated. Patients experiencing a flare-up from adult-onset Still's disease usually report extreme fatigue, swelling of the lymph nodes and, less commonly, fluid accumulation in the lungs and heart. In rare cases, AOSD can cause life-threatening complications, including hemophagocytic lymphohistiocytosis, IVDC, fulminant hepatitis, or disabling conditions such as aseptic meningitis and sensorineural hearing loss.


title: Adult-onset Still's disease

text: The cause of adult-onset Still's disease is unknown, but it presumably involves interleukin-1 (IL-1), since medications that block the action of IL-1β are effective treatments. Interleukin-18 is expressed at high levels.


title: Adult-onset Still's disease

text: The diagnosis is clinical, not based upon serology. At least seven sets of diagnostic criteria have been devised, however the Yamaguchi criteria have the highest sensitivity. Diagnosis requires at least five features, with at least two of these being major diagnostic criteria.


title: Adult-onset Still's disease

text: One set of 21 adult-onset Still's disease patients were divided into four types, according to clinical course patterns. These included monocyclic systemic disease, polycyclic systemic disease, chronic articular monocyclic systemic disease, and chronic articular polycyclic systemic disease. People with chronic articular disease and polyarticular disease were at higher risk to develop disabling arthritis.


title: Adult-onset Still's disease

text: Adult-onset Still's disease is treated with anti-inflammatory medications. Steroids such as prednisone are used to treat severe symptoms of Still's. Other commonly used medications include hydroxychloroquine, penicillamine, azathioprine, methotrexate, etanercept, anakinra, tocilizumab, cyclophosphamide, adalimumab, rituximab, and infliximab.


title: Adult-onset Still's disease

text: Newer medications target interleukin-1 (IL-1), particularly IL-1β. A randomized, multicenter trial reported better outcomes in a group of 12 patients treated with anakinra than in a group of 10 patients taking other disease-modifying antirheumatic drugs. In June 2020 FDA approved Ilaris (canakinumab) for the treatment of AOSD, this is the first FDA approved treatment for AOSD. Canakinumab is another anti-IL1 drug which selectively binds IL-1β and rilonacept which blocks both IL-1A and IL-1β. The monoclonal anti-IL6 antibody tocilizumab is another treatment option as effective as anakinra.


title: Adult-onset Still's disease

text: The condition "juvenile-onset Still's disease" is now usually grouped under juvenile rheumatoid arthritis. However, there are obvious similarities between the two conditions, and there is some evidence that they may be closely related.


title: Adult-onset Still's disease

text: Adult-onset Still's disease is rare and has been described all over the world. The number of new cases per year is estimated to be 1.6 per 1,000,000 population. The number of people currently affected is estimated at 1.5 cases per 100,000–1,000,000 population. Onset is most common in two age ranges, between ages 16–25 and between ages of 36–46 years.


title: Adult-onset Still's disease

text: Still's disease is named after English physician Sir George Frederic Still (1861–1941). The adult-onset version was characterized by E. G. Bywaters in 1971.


title: Adult-onset Still's disease

text: Researchers are investigating whether levels of a protein named calprotectin could be used to improve diagnosis and monitoring.


title: City status in the United Kingdom

text: City status in the United Kingdom is granted by the monarch of the United Kingdom to a select group of communities. , there are 76 cities in the United Kingdom—55 in England, seven in Wales, eight in Scotland, and six in Northern Ireland. Although it carries no special rights, the status of city can be a marker of prestige and confer local pride.


title: City status in the United Kingdom

text: The status does not apply automatically on the basis of any particular criterion, though in England and Wales it was traditionally given to towns with diocesan cathedrals. This association between having an Anglican cathedral and being called a city was established in the early 1540s when King Henry VIII founded dioceses (each having a cathedral in the see city) in six English towns and granted them city status by issuing letters patent.


title: City status in the United Kingdom

text: City status in Ireland was granted to far fewer communities than in England and Wales, and there are only two pre-19th-century cities in present-day Northern Ireland. In Scotland, city status did not explicitly receive any recognition by the state until the 19th century. At that time, a revival of grants of city status took place, first in England, where the grants were accompanied by the establishment of new cathedrals, and later in Scotland and Ireland. In the 20th century, it was explicitly recognised that the status of city in England and Wales would no longer be bound to the presence of a cathedral, and grants made since have been awarded to communities on a variety of criteria, including population size.


title: City status in the United Kingdom

text: The abolition of some corporate bodies as part of successive local-government reforms, beginning with the Municipal Corporations (Ireland) Act 1840, has deprived some ancient cities of their status. However, letters patent have been issued for most of the affected cities to ensure the continuation or restoration of their status. At present, Rochester and Elgin are the only former cities in the United Kingdom. The name "City" does not, in itself, denote city status; it may be appended to place names for historic association (e.g. White City) or for marketing or disambiguation (e.g. Stratford City). A number of large towns (such as those with over 200,000 residents) in the UK are bigger than some small cities, but cannot legitimately call themselves cities without the royal designation.


title: City status in the United Kingdom

text: The initial cities () of Britain were the fortified settlements organised by the Romans as the capitals of the Celtic tribes under Roman rule. The British clerics of the early Middle Ages later preserved a traditional list of the "28 Cities" () which was mentioned by Gildas and listed by Nennius.


title: City status in the United Kingdom

text: In the 16th century, a town was recognised as a city by the English Crown if it had a diocesan cathedral within its limits, for which 22 dioceses existed in England & Wales (see City status conferment further in the article). This association between having a cathedral and being called a city was established when Henry VIII founded new dioceses (each having a cathedral in the see city) in six English towns and also granted them city status by issuing letters patent, demonstrating these were discrete procedures. Some cities today are very small because they were granted city status in or before the 16th century, then were unaffected by population growth during the Industrial Revolution—notably Wells (population about 10,000) and St Davids (population about 2,000). After the 16th century, no new dioceses (and no new cities) were created until the 19th century in England (a further city was created in Ireland during the rule of King James I in the 17th century).


title: City status in the United Kingdom

text: A long-awaited resumption of creating dioceses began in 1836 with Ripon. Ripon Town Council assumed that this had elevated the town to the rank of a city, and started referring to itself as the "City and Borough of Ripon". The next diocese formed was Manchester and its Borough Council began informally to use the title "city". When Queen Victoria visited Manchester in 1851, widespread doubts surrounding its status were raised. The pretension was ended when the borough petitioned for city status, which was granted by letters patent in 1853. This eventually forced Ripon to regularise its position; its city status was recognised by Act of Parliament in 1865. From this year Ripon bore city status whilst the rapidly expanding conurbation of Leeds – in the Ripon diocese – did not. The Manchester case established a precedent that any municipal borough in which an Anglican see was established was entitled to petition for city status. Accordingly, Truro, St Albans, Liverpool, Newcastle upon Tyne and Wakefield were all officially designated as cities between 1877 and 1888.


title: City status in the United Kingdom

text: This was not without opposition from the Home Office, which dismissed St Albans as "a fourth or fifth rate market town" and objected to Wakefield's elevation on grounds of population. In one new diocese, Southwell, a city was not created, because it was a village without a borough corporation and therefore could not petition the Queen. The diocese covered the counties of Derbyshire and Nottinghamshire, and the boroughs of Derby and Nottingham were disappointed that they would not be able to claim the title of city.


title: City status in the United Kingdom

text: The link with Anglican dioceses was broken within England in 1889 when Birmingham successfully petitioned for city status (it was pre-empted in Ireland by Belfast in 1888) on the grounds of its large population and history of good local government. At the time of the grant, Birmingham lacked an Anglican cathedral, although the parish church later became a cathedral in 1905. This new precedent was followed by other large municipalities: Leeds and Sheffield became cities in 1893, and Bradford, Kingston upon Hull and Nottingham were honoured on the occasion of Queen Victoria's Diamond Jubilee in 1897. The last three had been the largest county boroughs outside the London area without city status.


title: City status in the United Kingdom

text: Between 1897 and 1914, applications were received from a number of other boroughs, but only Cardiff was successful in being designated a city in 1905 and granted a Lord Mayoralty as "the Metropolis of Wales".


title: City status in the United Kingdom

text: The London Government Act 1899 abolished the existing local authorities within the County of London and replaced them with 28 metropolitan boroughs. Among the bodies to be dissolved was the Court of Burgesses of the City of Westminster. William Burdett-Coutts, one of Westminster's members of parliament, brought forward an amendment to rename the proposed borough of Greater Westminster to "City of Westminster". This was intended to give "recognition to the title which the area ... had possessed for over three and a half centuries". He felt that if the status was not retained for the new borough it "must necessarily disappear altogether". The amendment was rejected by the government, however, with the First Lord of the Treasury, Arthur Balfour, believing it would be "an anomaly which, I think, would be not unnaturally resented by other districts which are as large in point of population as Westminster, although doubtless not so rich in historical associations". The government eventually relented, with Balfour stating that "as soon as the necessary arrangements under the London Government Act have been completed, there will be conferred on the borough of Westminster, as constituted under the Act, the title of city, originally conferred in the time of Henry VIII". Letters patent were duly issued granting the title of "city" to the newly created Metropolitan Borough of Westminster.


title: City status in the United Kingdom

text: In 1907, the Home Office and King Edward VII agreed on a policy that future applicants would have to meet certain criteria. This policy, which was not at the time made public, had the effect of stemming the number of city creations.


title: City status in the United Kingdom

text: However, well into the 20th century it was often assumed that the presence of a cathedral was sufficient to elevate a town to city status, and that for cathedral cities the city charters were recognising its city status rather than granting it. On this basis, the 1911 "Encyclopædia Britannica" said that Southwell and St Asaph were cities.


title: City status in the United Kingdom

text: The policy laid down by Edward VII was continued by his successor, George V, who ascended the throne in 1910. In 1911, an application for city status by Portsmouth was refused. Explaining the Home Secretary's reason for not recommending the King to approve the petition, the Lord Advocate stated:


title: City status in the United Kingdom

text: ...during the reign of his late Majesty it was found necessary, in order to maintain the value of the distinction, to lay down a rule as to the minimum population which should ordinarily, in connexion with other considerations, be regarded as qualifying a borough for that higher status.


title: City status in the United Kingdom

text: Following the First World War, the King made an official visit to Leicester in 1919 to commemorate its contributions to the military victory. The borough council had made several applications for city status since 1889, and took the opportunity of the visit to renew its request. Leicester had a population of approximately 230,000 at the previous census, but its petition was granted as an exception to the policy, as it was officially a restoration of a dignity lost in the past. When the county borough of Stoke-on-Trent applied for city status in 1925, it was initially refused as it had only 294,000 inhabitants. The decision was overturned, however, as it was felt to have outstanding importance as the centre of the pottery industry. The effective relaxation of the population rule led to applications from Portsmouth and Salford. The civil servants in the Home Office were minded to refuse both applications. In particular, Salford was felt to be "merely a scratch collection of 240,000 people cut off from Manchester by the river". Salford's case, however, was considered favourably by the Home Secretary, William Joynson-Hicks, who had once been a Member of Parliament (MP) for a neighbouring constituency of Manchester North West. Following protests from Portsmouth, which felt it had better credentials as a larger town and as the "first Naval Port of the kingdom", both applications were approved in 1926.


title: City status in the United Kingdom

text: In 1927, a Royal Commission on Local Government was examining local council areas and functions in England and Wales. The question arose as to which towns were entitled to be called cities, and the chairman, the Earl of Onslow, wrote to the Home Office to seek clarification. The Home Office replied with a memorandum that read:


title: City status in the United Kingdom

text: The title of a city which is borne by certain boroughs is a purely titular distinction. It has no connexion with the status of the borough in respect of local government and confers no powers or privileges. At the present time and for several centuries past the title has been obtained only by an express grant from the Sovereign effected by letters patent; but a certain number of cities possess the title by very ancient prescriptive right. There is no necessary connexion between the title of a city and the seat of a bishopric, and the creation of a new see neither constitutes the town concerned a city nor gives it any claim to the grant of letters patent creating it a city.


title: City status in the United Kingdom

text: In 1928, Plymouth submitted an application for city status. As the borough had more inhabitants than Portsmouth and had absorbed Devonport and East Stonehouse, the King agreed to the request. However, he indicated that he had "come to an end of city making", and Southampton's application in the following year was turned down. The next city to be created was Lancaster in 1937 as part of the celebrations of the coronation of King George VI and Queen Elizabeth. With a population of a little over 50,000, Lancaster was stated to be an exception due to the town's "long association with the crown" and because it was "the county town of the King's Duchy of Lancaster". Following the Second World War, members of Cambridge Borough Council made contact with Lancaster officials for assistance in their application. Cambridge became a city in 1951, again for "exceptional" reasons, as the only ancient seat of learning in the kingdom not a city or royal burgh and to coincide with the 750th anniversary of the borough's first charter of incorporation. Croydon also applied in 1951, but failed as it was felt not to have a sufficient identity apart from Greater London, and reports on the conduct of local government in the town were unfavourable.


title: City status in the United Kingdom

text: It was anticipated that the coronation of Elizabeth II in 1953 would lead to the creation of a city, and Wolverhampton, Preston and Southampton made approaches; the only civic honour given was that of a lord mayoralty to Coventry. Derby and Southwark made unsuccessful applications in 1955. The planned reorganisations by the Local Government Commissions for England and Wales from 1958 effectively blocked new city grants. Southampton lodged a petition in 1958. Initially refused in 1959, pending the decision of the commission, it was eventually allowed in 1964. In the meantime, the administration of London was reformed under the London Government Act 1963. While the City of London was permitted to continue in existence largely unchanged, Westminster was merged with two neighbouring authorities to form a new London borough from 1 April 1965. In December 1963 it was announced that a charter was to be granted incorporating the new authority as "Westminster", and that the Queen had accepted the advice of the Home Secretary to raise the London borough to the title and dignity of city. This example, of a successor local authority to a merged local government entity taking on that former entity's city status, was to be replicated in many instances as a result of the 1972/74 local government reforms across England and Wales (see below).


title: City status in the United Kingdom

text: With the establishment of the Royal Commission on Local Government in England in 1966, city grants were again in abeyance in England. Attempts by Derby, Teesside and Wolverhampton to become cities were not proceeded with. In Wales, Swansea campaigned for city status throughout the 1960s. The campaign came to a successful conclusion in 1969, in conjunction with the investiture of Charles, Prince of Wales.


title: City status in the United Kingdom

text: The Local Government Act 1972 abolished all existing local authorities outside London (other than parish councils) in England and Wales. This meant that the various local authorities that held city status ceased to exist on 1 April 1974. To preserve city status new letters patent were issued to the most relevant metropolitan borough, non-metropolitan district or successor parish councils created by the Act. Some of these came to cover local government districts many times wider than the previous city, even taking in many square miles of rural land outside the urban areas, for example the cities of Bradford, Leeds and Winchester. Three non-local authority preservations arose: here charter trustees were established for the cities of Lichfield and Salisbury (or New Sarum) being neither districts nor civil parishes, and special letters patent for a time preserved the city of Rochester.


title: City status in the United Kingdom

text: In 1977, as part of the celebrations of the Silver Jubilee of Elizabeth II, the Home Office identified nine candidates for city status: Blackburn, Brighton, Croydon, Derby, Dudley, Newport, Sandwell, Sunderland and Wolverhampton. Ultimately, Derby received the award as the largest non-metropolitan district not already designated a city. In April 1980 a parish council was created for Lichfield, and the charter trustees established six years earlier were dissolved. City status was temporarily lost until new letters patent were issued in November of the same year. In 1992, on the fortieth anniversary of the monarch's accession, it was announced that another town would be elevated to a city. An innovation on this occasion was that a competition was to be held, and communities would be required to submit applications. Sunderland was the successful applicant. This was followed in 1994 by the restoration of the dignity to St David's, historic see of a bishop. Since 2000, city status has been awarded to towns or local government districts by competition on special occasions. A large number of towns have applied for the honour in recent decades including Blackpool, Colchester, Croydon, Gateshead, Ipswich, Middlesbrough, Milton Keynes, Reading, Swindon and Warrington. Four successful applicants in England have become cities, as well as two in Wales; in 2000 for the Millennium celebrations, the new cities were Brighton and Hove and Wolverhampton; in 2002 for the Queen's Golden Jubilee it was Preston and Newport, and in 2012 for the Queen's Diamond Jubilee it was Chelmsford and St Asaph.


title: City status in the United Kingdom

text: From June 2021, submissions for city status were invited to mark the Platinum Jubilee of Elizabeth II in 2022. Places submitting bids (some for a second or subsequent time) included Bangor (Northern Ireland), Bournemouth, Doncaster, Dunfermline, Dudley, Marazion, Middlesbrough, Milton Keynes, Reading, St Andrews and Wrexham. Bids were also accepted from overseas territories and crown dependencies and George Town (in the Cayman Islands), Gibraltar, Stanley (in the Falkland Islands), Douglas and Peel (both in the Isle of Man) were among those applying. The competition closed on 8 December 2021 with 39 locations on the shortlist, and the winners were to be announced in June 2022.


title: City status in the United Kingdom

text: On 18 October 2021, the Prime Minister announced in Parliament that the Queen, in advance of the closing date, would accord city status to one of the applicants, Southend-on-Sea. This was in memory of Sir David Amess, the town's MP who was murdered three days earlier and had long pressed for the status. City status was officially granted by letters patent dated 26 January 2022. They were presented to Southend Borough Council by Charles, Prince of Wales, on 1 March 2022.


title: City status in the United Kingdom

text: An announcement on 20 May 2022 declared that eight new cities were to be created from the shortlist, with at least one in every UK country as well as in overseas territories. In England, Milton Keynes, Colchester and Doncaster were to be the recipients of the honour. Dunfermline, a previous royal capital of Scotland, was granted the privilege. Bangor in Northern Ireland was also a recipient, and the title in Wales was granted to Wrexham. Once these locations receive their letters patents later in 2022, this will increase the number of official mainland cities to 76, with 55 in England, eight in Scotland, seven in Wales, six in Northern Ireland. Outside the UK, Stanley, in the Falklands Islands, as well as Douglas, in the Isle of Man, were given the status, which will take the total to four cities after confirmations, with one in the Crown Dependencies and three in British Overseas Territories.


title: City status in the United Kingdom

text: Other than the cities of London and Westminster, no local authorities in the Greater London area have been granted city status. The Home Office had a policy of resisting any attempt by metropolitan boroughs to become cities even when their populations, and other proposed claims as qualifying criteria, might otherwise have made them eligible. It was felt that such a grant would undermine the status of the two existing cities in the capital. The Metropolitan Borough of Southwark made a number of applications, but in 1955 the borough's town clerk was told not to pursue the matter any further. Outside the boundaries of the county, the County Borough of Croydon made three applications, all of which were dismissed as it was not seen as being sufficiently separate from London. When the successor London Borough of Croydon applied in 1965 the Assistant Under Secretary of State summarised the case against Croydon: "...whatever its past history, it is now just part of the London conurbation and almost indistinguishable from many of the other Greater London boroughs".


title: City status in the United Kingdom

text: The same objections were made when the London Boroughs of Croydon and Southwark unsuccessfully entered the competition for city status to mark the millennium: Croydon was said to have "no particular identity of its own" while Southwark was "part of London with little individual identity". When the competition was held to mark the Golden Jubilee of 2002, Croydon made a sixth application, again unsuccessful. It was joined by the London Borough of Greenwich, which emphasised its royal and maritime connections, while claiming to be "to London what Versailles is to Paris". In this vein Greenwich joined Kingston-upon-Thames and Kensington and Chelsea in London in having the title of Royal Borough in 2012.


title: City status in the United Kingdom

text: Rochester was recognised as a city from 1211 to 1998. On 1 April 1974, the city council was abolished, becoming part of the Borough of Medway, a local government district in the county of Kent. However, under letters patent the former city council area was to continue to be styled the "City of Rochester" to "perpetuate the ancient name" and to recall "the long history and proud heritage of the said city". The city was unique, as it had no council or charter trustees and no mayor or civic head. In 1979, the Borough of Medway was renamed as Rochester-upon-Medway, and in 1982 further letters patent transferred the city status to the entire borough. On 1 April 1998, the existing local government districts of Rochester-upon-Medway and Gillingham were abolished and became the new unitary authority of Medway. Since it was the local government district that officially held city status under the 1982 letters patent, when it was abolished, it also ceased to be a city. Whilst the two other local government districts with city status (Bath and Hereford) that were abolished around this time decided to appoint charter trustees to maintain the existence of the city and the mayoralty, Rochester-upon-Medway City Council did not do so. Medway Council apparently only became aware of this when, in 2002, they discovered that Rochester was not on the Lord Chancellor's Office's list of cities. In 2010, it started to refer to the "City of Medway" in promotional material, but it was rebuked and instructed not to do so in future by the Advertising Standards Authority.


title: City status in the United Kingdom

text: Scotland had no cities by royal charter or letters patent before 1889. The nearest equivalent in pre-Union Scotland was the royal burgh. The term "city" was not always consistently applied, and there were doubts over the number of officially designated cities. The royal burghs of Edinburgh and Perth anciently used the title "civitas", but the term "city" does not seem to have been used before the 15th century. Unlike the situation in England, in Scotland there was no link between the presence of a cathedral and the title of "city". Aberdeen, Glasgow and Edinburgh were accepted as cities by ancient usage by the 18th century, while Perth and Elgin also used the title. In 1856, the burgh of Dunfermline resolved to use the title of "city" in all official documents in the future, based on long usage and its former status as a royal capital. The status was not officially recognised until 2022.


title: City status in the United Kingdom

text: In 1889, Dundee was granted city status by letters patent. The grant by formal document led to doubts about the use of the title "city" by other burghs. In 1891, the city status of Aberdeen was confirmed when the burgh was enlarged by local Act of Parliament. The Royal Burgh of Inverness applied for promotion to a city as part of the Jubilee honours in 1897. The request was not granted, partly because it would draw attention to the lack of any charter granting the title to existing cities. Aberdeen, Dundee, Edinburgh and Glasgow were constituted "counties of cities" by the Local Government (Scotland) Act 1929. The Act made no statement on the title "city" for any other burgh. In 1969, the Home Secretary, James Callaghan, stated that there were six cities in Scotland (without naming them) and Aberdeen, Dundee, Edinburgh, Elgin, Glasgow and Perth were the only burghs listed as cities in 1972.


title: City status in the United Kingdom

text: The Local Government (Scotland) Act 1973 completely reorganised Scotland's local administration in 1975. All burghs were abolished, and a system of districts created. The four districts of Aberdeen, Edinburgh, Dundee and Glasgow had "City" included in their titles by the Act. The 1975 districts were replaced with the present council areas in 1996 by the Local Government etc. (Scotland) Act 1994, and the same four cities were designated. Since the 1996 reorganisation, three more Scottish cities have been designated: Inverness as part of the millennium celebrations, Stirling in 2002 to commemorate Queen Elizabeth II's Golden Jubilee and Perth in 2012 to mark the Queen's Diamond Jubilee. In the case of these three cities, there are no city councils and no formal boundaries. In January 2008, a petition to matriculate armorial bearings for the City of Inverness was refused by Lord Lyon King of Arms on the grounds that there is no corporate body or legal persona to whom arms can be granted.


title: City status in the United Kingdom

text: City status in Ireland tended historically to be granted by royal charter. There are many towns in Ireland with Church of Ireland cathedrals that have never been called cities. In spite of this, Armagh was considered a city, by virtue of its being the seat of the Primate of All Ireland, until the abolition of Armagh's city corporation by the Municipal Corporations (Ireland) Act 1840. The only historic city with a charter in present-day Northern Ireland is Derry. Derry was given its first charter by James I in 1604, but the garrison was attacked and destroyed by Cahir O'Doherty in 1608. The present city is the result of a second charter granted in 1613 to members of the London guilds, as part of the Plantation of Ulster, providing for the building of a walled city, which was renamed Londonderry.


title: City status in the United Kingdom

text: In 1887, the Golden Jubilee of Queen Victoria was celebrated, and the Borough of Belfast submitted a memorial to the Lord Lieutenant of Ireland seeking city status. Belfast based its claim on its similarity to two English boroughs that had received the honour—the seaport of Liverpool and the textile centre of Manchester—and the fact that it had (at the time) a larger population than the City of Dublin. Following some legal debate, city status was conferred in 1888. The grant of the honour on the grounds of being a large industrial town, rather than a diocesan centre, was unprecedented. Belfast's example was soon followed by Birmingham in England and Dundee in Scotland.


title: City status in the United Kingdom

text: In 1994, Armagh's city status was restored. In 2002, Lisburn and Newry were two of the five towns in the UK that were granted city status by Queen Elizabeth II to mark her Golden Jubilee. In the case of Lisburn, the status extends to the entire local government district. Newry, like Inverness and Stirling in Scotland, has no formal boundaries or city council. The letters patent were presented to representatives of Newry and Mourne District Council on behalf of the city.


title: City status in the United Kingdom

text: During the British Empire, the Colonial Office had the power to declare cities in Crown colonies by letters patent when appointing bishops. When the Bishop of Guyana was created in 1842, Georgetown (then part of British Guiana) was officially declared the "City of Georgetown". The same process was followed for Gibraltar, Jamestown, St Helena, Bridgetown, Barbados, St. John's, Antigua and Barbuda, Victoria, Hong Kong and Nassau, Bahamas. Most of these have since gained independence from the United Kingdom, but Gibraltar and St Helena remain British Overseas Territories. This practice ended in 1865, and led to legal disputes about whether these letters patent were valid or not in territories with responsible government (primarily those in present day Australia, Canada, New Zealand and South Africa). Goulburn in Australia for example found itself declared a city twice - once by letters patent in 1863 and once by law in 1885 after doubts arose to its status.


title: City status in the United Kingdom

text: Hamilton, Bermuda was named as a city in 1897 as part of the celebration of the Diamond Jubilee of Queen Victoria. In 2022, as part of the Platinum Jubilee of Elizabeth II, Port Stanley in the Falkland Islands was also declared a city. Although previously named a city, Gibraltar also applied for city status, as did George Town, Cayman Islands. Following the competition, researchers at The National Archives confirmed that Gibraltar's city status was still in effect, and that the territory had been missing from the official list of cities for the past 140 years.


title: City status in the United Kingdom

text: If a town wishes to obtain the title of a city the proper method of procedure is to address a petition to the King through the Home Office. It is the duty of the Home Secretary to submit such petitions to his Majesty and to advise his Majesty to the reply to be returned. It is a well-established principle that the grant of the title is only recommended in the case of towns of the first rank in population, size and importance, and having a distinctive character and identity of their own. At the present day, therefore, it is only rarely and in exceptional circumstances that the title is given.


title: City status in the United Kingdom

text: A town can now apply for city status by submitting an application to the Lord Chancellor, who makes recommendations to the sovereign. Competitions for new grants of city status have been held to mark special events, such as coronations, royal jubilees or the Millennium.


title: City status in the United Kingdom

text: Some cities in England, Wales and Northern Ireland have the further distinction of having a lord mayor rather than a simple mayor – in Scotland, the equivalent is the lord provost. Lord mayors have the right to be styled "The Right Worshipful The Lord Mayor". The lord mayors and provosts of Belfast, Cardiff, Edinburgh, Glasgow, the City of London and York have the further right to be styled "The Right Honourable the Lord Mayor" (or Provost), although they are not members of the Privy Council as this style usually indicates. The style is associated with the office, not the person holding it, so "The Right Worshipful Joseph Bloggsworthy" would be incorrect.


title: City status in the United Kingdom

text: There are currently 70 recognised cities (including 31 lord mayoralties or lord provostships) in the UK: 52 cities (23 lord mayoralties) in England, six cities (two lord mayoralties) in Wales, seven cities (four lord provostships) in Scotland and five cities (two lord mayoralties) in Northern Ireland.


title: City status in the United Kingdom

text: In the Republic of Ireland, the ceremonial head of the city government of Dublin is the Lord Mayor of Dublin. This title was granted by Charles II in 1665 when Dublin was part of the Kingdom of Ireland. Whilst the 1665 letters patent provided for the Lord Mayor to hold the formal title of Right Honourable, this was repealed in 2001. There is also a Lord Mayor of Cork, a title granted in 1900 when Cork was part of the (then) United Kingdom of Great Britain and Ireland.


title: City status in the United Kingdom

text: In modern practice, competitions are held for cities that wish to gain the distinction of a lord mayor. The 2002 competition was entered by Bath, Cambridge, Carlisle, Chichester, Derby, Exeter, Gloucester, Lancaster, Lincoln, St Albans, St Davids, Salford, Southampton, Sunderland, Truro, Wolverhampton and Worcester; the successful candidate was Exeter. In 2012 a further competition was held, as part of the Diamond Jubilee celebrations, with Armagh receiving the distinction. Other than Armagh, eleven cities had entered the contest in 2012, namely: Cambridge, Derby, Gloucester, Lancaster, Newport, Peterborough, Salford, Southampton, St Albans, Sunderland, and Wakefield.


title: City status in the United Kingdom

text: Since local government reorganisation in 1974 city status has been awarded to a number of local government districts which are not themselves towns. Each includes a number of towns and villages outside the urban area from which the district takes its name. In some of these cases city status was awarded to districts where the largest settlement had city status before 1974. In other cases a borough was formed to govern an area covering several towns and then city status was granted to the borough. The largest "city" district in terms of area is the City of Carlisle, which covers some of mostly rural landscape in the north of England, and is larger than smaller counties such as Merseyside or Rutland. Such cities include:


title: City status in the United Kingdom

text: There are some cities where the local government district is in fact smaller than the historical or natural boundaries of the city. Examples include: Manchester, where the traditional area associated includes areas of the neighbouring authorities of Trafford, Tameside, Oldham, Bury and the City of Salford; Kingston upon Hull, where surrounding areas and villages that are effectively suburbs, such as Cottingham, come under East Riding of Yorkshire Council; Glasgow, where suburban areas of the city are located in East Dunbartonshire, East Renfrewshire, North Lanarkshire, Renfrewshire, South Lanarkshire and West Dunbartonshire; Wolverhampton and London.


title: City status in the United Kingdom

text: The holding of city status gives a settlement no special rights other than that of calling itself a "city". Nonetheless, this appellation carries its own prestige and, consequently, competitions for the status are hard-fought.


title: City status in the United Kingdom

text: Historically, city status could only be granted to incorporated towns. The grant was specifically awarded to the relevant local government area such as a civil parish or borough. However, recent grants have used a looser wording, where the status is awarded to the "town". In most cases the "town" is held to be coterminous with the relevant local government area, such that the city status holder is the corporate body of the council. Examples include the Letters Patent awarded to the "Towns of Brighton and Hove", the "Town of Wolverhampton" and the "Town of Newport in the County Borough of Newport". In each case the existing borough council became the city council.


title: City status in the United Kingdom

text: Most cities have city councils, which have varying powers depending on the country and type of settlement.


title: City status in the United Kingdom

text: Thirteen of the 55 cities in England are in metropolitan counties and their city councils are single-tier metropolitan district councils. Outside the metropolitan counties fourteen cities are unitary authorities, and fifteen have ordinary district councils, which are subordinate to their local county council. In London the Westminster City Council functions as a London borough council, and the City of London Corporation is the council for the City of London. Eight smaller episcopal cities such as Ripon and Wells are neither local government districts nor within a 'local government district with city status', and have city councils which are parish councils, with limited powers. Two cities (Bath and Chester) have no city council, while Durham has a 'city' parish council – these however, maintain the status through charter trustees on behalf of their prior district areas which held city status before being abolished in 1996 and 2009.


title: City status in the United Kingdom

text: Aberdeen, Dundee, Edinburgh and Glasgow are themselves council areas and have their own city councils. The cities of Dunfermline, Perth, Stirling and Inverness are part of council areas which do not have city status, and have no city councils. Stirling Council's application for city status was specifically for the urban area of the (now former) Royal Burgh of Stirling and included proposed city boundaries which are much smaller than Stirling council area.


title: City status in the United Kingdom

text: Cardiff, Newport, Swansea and Wrexham are principal areas and have city councils. The city councils of Bangor, St Asaph and St Davids are community councils with limited powers.


title: City status in the United Kingdom

text: Belfast City Council is a local government district council. Since the local government reforms of 2015 the four other cities of Armagh, Derry, Lisburn and Newry form parts of wider districts and do not have their own councils.


title: City status in the United Kingdom

text: City status is conferred by letters patent and not by a royal charter (except historically in Ireland). There are twenty towns in England and Wales that were recognised as cities by "ancient prescriptive right"; none of these communities had been formally declared a city, but they had all used the title since "time immemorial", that is, before 3 September 1189, and had been granted some form of privilege such as freedoms by way of a charter or being given borough or corporation status. A list of these ancient cities was produced by the Home Office in 1927 and were:


title: City status in the United Kingdom

text: These twenty cities were concurrent with 22 ancient diocese (pre-English Reformation) locations. Bath and Wells being one diocese, the remaining three are in Wales:


title: City status in the United Kingdom

text: The holding of city status brings no special benefits other than the right to be called a city. All cities where a local government unit that holds that status is abolished have to be re-issued with letters patent reconfirming city status following local government reorganisation where that holder has been abolished. This process was followed by a number of cities since 1974, and York and Hereford's status was confirmed twice, in 1974 and again in the 1990s. Failure to do so leads to the loss of city status as happened at Rochester in 1998 ("see above"), and also previously in St David's and Armagh, although both of these latter have regained city status since losing it. These three had been cities since time immemorial before the loss of city status.


title: City status in the United Kingdom

text: There are currently 76 officially designated cities in the UK, of which 17 have been created since 2000 in competitions to celebrate the new millennium and Queen Elizabeth II's Golden Jubilee in 2002, Diamond Jubilee in 2012, and Platinum Jubilee in 2022. The designation is highly sought after, with over 40 communities submitting bids at recent competitions.


title: City status in the United Kingdom

text: While cities are regularly ranked by the number of residents, this is not an ideal measure. Population can vary based on the number and type of residences present, and has to be limited to an area. As mentioned earlier in the article, the official area of a city in the UK is typically the coverage up to a local government/council boundary, there being a variety of council bodies. However, there are exceptions depending on the UK constituent country and whether the council has since been abolished.


title: City status in the United Kingdom

text: Such a boundary can typically contain a built up (urban) area, and a surrounding, less populated rural landscape. Inversely, the area of a city can be entirely built up, with that urban environment spilling over a boundary into another area which does not have city status. That wider urban area can still be considered in everyday parlance locally as a whole 'city' although it is not a formal designation.


title: City status in the United Kingdom

text: With the 'square mile' City of London being in the middle of a huge urban area, it can be suggested that 'small' should be applied to only cities with minimal urban areas that have nearby surrounding areas of countryside and so is visibly representative of the term, Wells being more suitable in this regard as the smallest standalone city council area. Therefore, sizing can be interpreted in a number of ways, and below are top 5 lists of the smallest and largest cities ranked by population, city council area, and urban area.


title: City status in the United Kingdom

text: The least populous cities on all of British territory are Jamestown in St Helena, Ascension and Tristan da Cunha (pop. 629) and Hamilton in Bermuda (pop. 854).


title: City status in the United Kingdom

text: As noted above, in ordinary discourse, "city" can refer to any large settlement, with no fixed limit. There are certain towns with large urban areas that could qualify for city status on the grounds of population size. Some have applied for city status and had the application turned down.


title: City status in the United Kingdom

text: The report "Key Statistics for Built-Up Areas 2011" published by the Office for National Statistics shows that, at the 2011 Census, the following were the largest urban areas in the United Kingdom not having a city as a component. The name shown is the largest town in the area:


title: City status in the United Kingdom

text: Since being the seat of an Anglican diocese is no longer sufficient or necessary to gain city status, some cathedral towns exist:


title: City status in the United Kingdom

text: The 1911 "Encyclopædia Britannica" refers to Southwell as a city, and in 1949 Bury St Edmunds is referred to as a city.


title: City status in the United Kingdom

text: In total there are 15 English and Welsh cities that have never had Anglican cathedrals within their borders – Brighton and Hove, Cambridge, Hull, Lancaster, Leeds, Nottingham, Plymouth, Preston, Salford, Southampton, Southend-on-Sea, Stoke-on-Trent, Sunderland, Swansea, and Wolverhampton.


title: City status in the United Kingdom

text: Bath Abbey was once a diocesan cathedral, as was Westminster Abbey briefly during the reign of Henry VIII. These cities retained their city status despite their cathedrals losing that status.


title: City status in the United Kingdom

text: The national church of Scotland, the Church of Scotland, is presbyterian in governance (not recognising authority of bishops), and thus has high kirks rather than cathedrals. However, the pre-Reformation dioceses do have extant cathedrals, most notably at Glasgow and Aberdeen, which remain in use by the Church of Scotland and continue to bear the honorific title of cathedral. Others (such as that of St Andrews) are now in ruins.


title: City status in the United Kingdom

text: As noted above, both Perth and Elgin were recognised as cities before 1975; Perth's city status was restored in 2012. Additionally, five other pre-Reformation sees—Brechin, Dunblane, Dunkeld, Kirkwall and St Andrews—are often referred to as cities, notably in names associated with the settlements (e.g. 'City of Brechin and District' community council. and Brechin City F.C., City Road in St Andrews). Dornoch, Fortrose, Lismore, Saddell and Whithorn also possess pre-Reformation cathedrals but have never been described as cities.


title: City status in the United Kingdom

text: Towns with non-Church of Scotland, post-Reformation cathedrals which are not recognised as cities are Ayr (R.C.), Millport (Episcopal), Oban (R.C.), Motherwell (R.C.) and Paisley (R.C.). Of these, Ayr, Motherwell and Paisley have larger populations than Perth, Stirling and Inverness, and both Ayr and Paisley have formally made a bid for city status during the millennium competition.


title: City status in the United Kingdom

text: Of settlements granted city status in the 21st century, Inverness (awarded 2001) possesses an Episcopal cathedral (1866), but none under the auspices of the Church of Scotland. Stirling (awarded 2002) has never had a cathedral of any kind. Perth (reinstated 2012) has an Episcopal cathedral dating from 1860, but no pre-Reformation establishment.


title: City status in the United Kingdom

text: In Northern Ireland, as noted above, possession of a diocesan cathedral has never (except in the anomalous case of Armagh) been sufficient to attain this status. In addition, the Church of Ireland was disestablished in 1871.


title: City status in the United Kingdom

text: In spite of this, the 1911 "Encyclopædia Britannica" refers to Armagh (Armagh had lost city status in 1840) and Lisburn as cities. Armagh subsequently regained city status formally in 1994 and Lisburn achieved city status in 2002.


title: City status in the United Kingdom

text: There are four towns in Northern Ireland with Church of Ireland cathedrals that do not have city status—Clogher, Downpatrick, Dromore and Enniskillen.


title: City status in the United Kingdom

text: Newry is the only city in Northern Ireland that does not have a Church of Ireland cathedral within its borders.


title: City status in the United Kingdom

text: A number of towns describe themselves as cities (at least in some contexts), despite not having the requisite Charter.


title: Byzantine fault

text: A Byzantine fault (also Byzantine generals problem, interactive consistency, source congruency, error avalanche, Byzantine agreement problem, and Byzantine failure) is a condition of a computer system, particularly distributed computing systems, where components may fail and there is imperfect information on whether a component has failed. The term takes its name from an allegory, the "Byzantine generals problem", developed to describe a situation in which, in order to avoid catastrophic failure of the system, the system's actors must agree on a concerted strategy, but some of these actors are unreliable.


title: Byzantine fault

text: In a Byzantine fault, a component such as a server can inconsistently appear both failed and functioning to failure-detection systems, presenting different symptoms to different observers. It is difficult for the other components to declare it failed and shut it out of the network, because they need to first reach a consensus regarding which component has failed in the first place. Byzantine fault tolerance (BFT) is the resiliency of a fault-tolerant computer system to such conditions.


title: Byzantine fault

text: In its simplest form, a number of generals are attacking a fortress and they must decide as a group whether to attack or retreat. Some generals may prefer to attack, while others prefer to retreat. The important thing is that all generals agree on a common decision, for a halfhearted attack by a few generals would become a rout, and would be worse than either a coordinated attack or a coordinated retreat.


title: Byzantine fault

text: The problem is complicated by the presence of treacherous generals who may not only cast a vote for a suboptimal strategy, they may do so selectively. For instance, if nine generals are voting, four of whom support attacking while four others are in favor of retreat, the ninth general may send a vote of retreat to those generals in favor of retreat, and a vote of attack to the rest. Those who received a retreat vote from the ninth general will retreat, while the rest will attack (which may not go well for the attackers). The problem is complicated further by the generals being physically separated and having to send their votes via messengers who may fail to deliver votes or may forge false votes.


title: Byzantine fault

text: Byzantine fault tolerance can be achieved if the loyal (non-faulty) generals have a majority agreement on their strategy. There can be a default vote value given to missing messages. For example, missing messages can be given a "null" value. Further, if the agreement is that the null votes are in the majority, a pre-assigned default strategy can be used (e.g. retreat).


title: Byzantine fault

text: The typical mapping of this story onto computer systems is that the computers are the generals and their digital communication system links are the messengers. Although the problem is formulated in the analogy as a decision-making and security problem, in electronics, it cannot be solved by cryptographic digital signatures alone, because failures such as incorrect voltages can propagate through the encryption process. Thus, a component may appear functioning to one component and faulty to another, which prevents forming a consensus as to whether the component is faulty or not.


title: Byzantine fault

text: A Byzantine fault is any fault presenting different symptoms to different observers. A Byzantine failure is the loss of a system service due to a Byzantine fault in systems that require consensus among distributed nodes.


title: Byzantine fault

text: The objective of Byzantine fault tolerance is to be able to defend against failures of system components with or without symptoms that prevent other components of the system from reaching an agreement among themselves, where such an agreement is needed for the correct operation of the system.


title: Byzantine fault

text: The remaining operationally correct components of a Byzantine fault tolerant system will be able to continue providing the system's service as originally intended, assuming there are a sufficient number of accurately-operating components to maintain the service.


title: Byzantine fault

text: Byzantine failures are considered the most general and most difficult class of failures among the failure modes. The so-called fail-stop failure mode occupies the simplest end of the spectrum. Whereas fail-stop failure mode simply means that the only way to fail is a node crash, detected by other nodes, Byzantine failures imply no restrictions, which means that the failed node can generate arbitrary data, including data that makes it appear like a functioning node. Thus, Byzantine failures can confuse failure detection systems, which makes fault tolerance difficult. Despite the analogy, a Byzantine failure is not necessarily a security problem involving hostile human interference: it can arise purely from electrical or software faults.


title: Byzantine fault

text: The terms fault and failure are used here according to the standard definitions originally created by a joint committee on "Fundamental Concepts and Terminology" formed by the IEEE Computer Society's Technical Committee on Dependable Computing and Fault-Tolerance and IFIP Working Group 10.4 on Dependable Computing and Fault Tolerance. See also dependability.


title: Byzantine fault

text: Byzantine fault tolerance is only concerned with broadcast consistency, that is, the property that when one component broadcasts a single consistent value to other components (i.e., sends the same value to the other components), they all receive exactly the same value, or in the case that the broadcaster is not consistent, the other components agree on a common value. This kind of fault tolerance does not encompass the correctness of the value itself; for example, an adversarial component that deliberately sends an incorrect value, but sends that same value consistently to all components, will not be caught in the Byzantine fault tolerance scheme.


title: Byzantine fault

text: Given a system of components, of which are dishonest, and assuming only point-to-point channel between all the components.


title: Byzantine fault

text: Whenever a component tries to broadcast a value , the other components are allowed to discuss with each other and verify the consistency of 's broadcast, and eventually settle on a common value .


title: Byzantine fault

text: Property: The system is said to resist Byzantine faults if a component can broadcast a value , and then:


title: Byzantine fault

text: Variants: The problem has been studied in the case of both synchronous and asynchronous communications.


title: Byzantine fault

text: The communication graph above is assumed to be the complete graph (i.e. each component can discuss with every other), but the communication graph can be restricted.


title: Byzantine fault

text: It can also be relaxed in a more "realistic" problem where the faulty components do not collude together in an attempt to lure the others into error. It is in this setting that practical algorithms have been devised.


title: Byzantine fault

text: The problem of obtaining Byzantine consensus was conceived and formalized by Robert Shostak, who dubbed it the "interactive consistency" problem. This work was done in 1978 in the context of the NASA-sponsored SIFT project in the Computer Science Lab at SRI International. SIFT (for Software Implemented Fault Tolerance) was the brain child of John Wensley, and was based on the idea of using multiple general-purpose computers that would communicate through pairwise messaging in order to reach a consensus, even if some of the computers were faulty.


title: Byzantine fault

text: At the beginning of the project, it was not clear how many computers in total were needed to guarantee that a conspiracy of "n" faulty computers could not "thwart" the efforts of the correctly-operating ones to reach consensus. Shostak showed that a minimum of 3"n+"1 are needed, and devised a two-round 3"n+1" messaging protocol that would work for "n"=1. His colleague Marshall Pease generalized the algorithm for any n > 0, proving that 3"n"+1 is both necessary and sufficient. These results, together with a later proof by Leslie Lamport of the sufficiency of 3"n" using digital signatures, were published in the seminal paper, "Reaching Agreement in the Presence of Faults." The authors were awarded the 2005 Edsger W. Dijkstra Prize for this paper.


title: Byzantine fault

text: To make the interactive consistency problem easier to understand, Lamport devised a colorful allegory in which a group of army generals formulate a plan for attacking a city. In its original version, the story cast the generals as commanders of the Albanian army. The name was changed, eventually settling on "Byzantine", at the suggestion of Jack Goldberg to future-proof any potential offense giving. This formulation of the problem, together with some additional results, were presented by the same authors in their 1982 paper, "The Byzantine Generals Problem".


title: Byzantine fault

text: Several examples of Byzantine failures that have occurred are given in two equivalent journal papers. These and other examples are described on the NASA DASHlink web pages.


title: Byzantine fault

text: Byzantine errors were observed infrequently and at irregular points during endurance testing for the newly constructed "Virginia" class submarines, at least through 2005 (when the issues were publicly reported).


title: Byzantine fault

text: One example of BFT in use is Bitcoin, a peer-to-peer digital cash system. The Bitcoin network works in parallel to generate a blockchain with proof-of-work allowing the system to overcome Byzantine failures and reach a coherent global view of the system's state. Some proof of stake blockchains also use BFT algorithms.


title: Byzantine fault

text: Some aircraft systems, such as the Boeing 777 Aircraft Information Management System (via its ARINC 659 SAFEbus network),


title: Byzantine fault

text: the Boeing 777 flight control system, and the Boeing 787 flight control systems use Byzantine fault tolerance; because these are real-time systems, their Byzantine fault tolerance solutions must have very low latency. For example, SAFEbus can achieve Byzantine fault tolerance within the order of a microsecond of added latency. The SpaceX Dragon considers Byzantine fault tolerance in its design.


title: Byzantine fault

text: Byzantine fault tolerance mechanisms use components that repeat an incoming message (or just its signature) to other recipients of that incoming message. All these mechanisms make the assumption that the act of repeating a message blocks the propagation of Byzantine symptoms. For systems that have a high degree of safety or security criticality, these assumptions must be proven to be true to an acceptable level of fault coverage. When providing proof through testing, one difficulty is creating a sufficiently wide range of signals with Byzantine symptoms. Such testing likely will require specialized fault injectors.


title: Byzantine fault

text: Several early solutions were described by Lamport, Shostak, and Pease in 1982. They began by noting that the Generals' Problem can be reduced to solving a "Commander and Lieutenants" problem where loyal Lieutenants must all act in unison and that their action must correspond to what the Commander ordered in the case that the Commander is loyal:


title: Byzantine fault

text: Several system architectures were designed c. 1980 that implemented Byzantine fault tolerance. These include: Draper's FTMP, Honeywell's MMFCS, and SRI's SIFT.


title: Byzantine fault

text: In 1999, Miguel Castro and Barbara Liskov introduced the "Practical Byzantine Fault Tolerance" (PBFT) algorithm, which provides high-performance Byzantine state machine replication, processing thousands of requests per second with sub-millisecond increases in latency.


title: Byzantine fault

text: After PBFT, several BFT protocols were introduced to improve its robustness and performance. For instance, Q/U, HQ, Zyzzyva, and ABsTRACTs, addressed the performance and cost issues; whereas other protocols, like Aardvark and RBFT, addressed its robustness issues. Furthermore, Adapt tried to make use of existing BFT protocols, through switching between them in an adaptive way, to improve system robustness and performance as the underlying conditions change. Furthermore, BFT protocols were introduced that leverage trusted components to reduce the number of replicas, e.g., A2M-PBFT-EA and MinBFT.


title: Predation

text: Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill the host) and parasitoidism (which always does, eventually). It is distinct from scavenging on dead prey, though many predators also scavenge; it overlaps with herbivory, as seed predators and destructive frugivores are predators.


title: Predation

text: Predators may actively search for or pursue prey or wait for it, often concealed. When prey is detected, the predator assesses whether to attack it. This may involve ambush or pursuit predation, sometimes after stalking the prey. If the attack is successful, the predator kills the prey, removes any inedible parts like the shell or spines, and eats it.


title: Predation

text: Predators are adapted and often highly specialized for hunting, with acute senses such as vision, hearing, or smell. Many predatory animals, both vertebrate and invertebrate, have sharp claws or jaws to grip, kill, and cut up their prey. Other adaptations include stealth and aggressive mimicry that improve hunting efficiency.


title: Predation

text: Predation has a powerful selective effect on prey, and the prey develop antipredator adaptations such as warning coloration, alarm calls and other signals, camouflage, mimicry of well-defended species, and defensive spines and chemicals. Sometimes predator and prey find themselves in an evolutionary arms race, a cycle of adaptations and counter-adaptations. Predation has been a major driver of evolution since at least the Cambrian period.


title: Predation

text: At the most basic level, predators kill and eat other organisms. However, the concept of predation is broad, defined differently in different contexts, and includes a wide variety of feeding methods; and some relationships that result in the prey's death are not generally called predation. A parasitoid, such as an ichneumon wasp, lays its eggs in or on its host; the eggs hatch into larvae, which eat the host, and it inevitably dies. Zoologists generally call this a form of parasitism, though conventionally parasites are thought not to kill their hosts. A predator can be defined to differ from a parasitoid in that it has many prey, captured over its lifetime, where a parasitoid's larva has just one, or at least has its food supply provisioned for it on just one occasion.


title: Predation

text: There are other difficult and borderline cases. Micropredators are small animals that, like predators, feed entirely on other organisms; they include fleas and mosquitoes that consume blood from living animals, and aphids that consume sap from living plants. However, since they typically do not kill their hosts, they are now often thought of as parasites. Animals that graze on phytoplankton or mats of microbes are predators, as they consume and kill their food organisms; but herbivores that browse leaves are not, as their food plants usually survive the assault. When animals eat seeds ("seed predation" or "granivory") or eggs ("egg predation"), they are consuming entire living organisms, which by definition makes them predators.


title: Predation

text: Scavengers, organisms that only eat organisms found already dead, are not predators, but many predators such as the jackal and the hyena scavenge when the opportunity arises. Among invertebrates, social wasps (yellowjackets) are both hunters and scavengers of other insects.


title: Predation

text: While examples of predators among mammals and birds are well known, predators can be found in a broad range of taxa including arthropods. They are common among insects, including mantids, dragonflies, lacewings and scorpionflies. In some species such as the alderfly, only the larvae are predatory (the adults do not eat). Spiders are predatory, as well as other terrestrial invertebrates such as scorpions; centipedes; some mites, snails and slugs; nematodes; and planarian worms. In marine environments, most cnidarians (e.g., jellyfish, hydroids), ctenophora (comb jellies), echinoderms (e.g., sea stars, sea urchins, sand dollars, and sea cucumbers) and flatworms are predatory. Among crustaceans, lobsters, crabs, shrimps and barnacles are predators, and in turn crustaceans are preyed on by nearly all cephalopods (including octopuses, squid and cuttlefish).


title: Predation

text: Seed predation is restricted to mammals, birds, and insects but is found in almost all terrestrial ecosystems. Egg predation includes both specialist egg predators such as some colubrid snakes and generalists such as foxes and badgers that opportunistically take eggs when they find them.


title: Predation

text: Some plants, like the pitcher plant, the Venus fly trap and the sundew, are carnivorous and consume insects. Methods of predation by plants varies greatly but often involves a food trap, mechanical stimulation, and electrical impulses to eventually catch and consume its prey. Some carnivorous fungi catch nematodes using either active traps in the form of constricting rings, or passive traps with adhesive structures.


title: Predation

text: Many species of protozoa (eukaryotes) and bacteria (prokaryotes) prey on other microorganisms; the feeding mode is evidently ancient, and evolved many times in both groups. Among freshwater and marine zooplankton, whether single-celled or multi-cellular, predatory grazing on phytoplankton and smaller zooplankton is common, and found in many species of nanoflagellates, dinoflagellates, ciliates, rotifers, a diverse range of meroplankton animal larvae, and two groups of crustaceans, namely copepods and cladocerans.


title: Predation

text: To feed, a predator must search for, pursue and kill its prey. These actions form a foraging cycle. The predator must decide where to look for prey based on its geographical distribution; and once it has located prey, it must assess whether to pursue it or to wait for a better choice. If it chooses pursuit, its physical capabilities determine the mode of pursuit (e.g., ambush or chase). Having captured the prey, it may also need to expend energy "handling" it (e.g., killing it, removing any shell or spines, and ingesting it).


title: Predation

text: Predators have a choice of search modes ranging from "sit-and-wait" to "active" or "widely foraging". The sit-and-wait method is most suitable if the prey are dense and mobile, and the predator has low energy requirements. Wide foraging expends more energy, and is used when prey is sedentary or sparsely distributed. There is a continuum of search modes with intervals between periods of movement ranging from seconds to months. Sharks, sunfish, Insectivorous birds and shrews are almost always moving while web-building spiders, aquatic invertebrates, praying mantises and kestrels rarely move. In between, plovers and other shorebirds, freshwater fish including crappies, and the larvae of coccinellid beetles (ladybirds), alternate between actively searching and scanning the environment.


title: Predation

text: Prey distributions are often clumped, and predators respond by looking for "patches" where prey is dense and then searching within patches. Where food is found in patches, such as rare shoals of fish in a nearly empty ocean, the search stage requires the predator to travel for a substantial time, and to expend a significant amount of energy, to locate each food patch. For example, the black-browed albatross regularly makes foraging flights to a range of around , up to a maximum foraging range of for breeding birds gathering food for their young. With static prey, some predators can learn suitable patch locations and return to them at intervals to feed. The optimal foraging strategy for search has been modelled using the marginal value theorem.


title: Predation

text: Search patterns often appear random. One such is the Lévy walk, that tends to involve clusters of short steps with occasional long steps. It is a good fit to the behaviour of a wide variety of organisms including bacteria, honeybees, sharks and human hunter-gatherers.


title: Predation

text: Having found prey, a predator must decide whether to pursue it or keep searching. The decision depends on the costs and benefits involved. A bird foraging for insects spends a lot of time searching but capturing and eating them is quick and easy, so the efficient strategy for the bird is to eat every palatable insect it finds. By contrast, a predator such as a lion or falcon finds its prey easily but capturing it requires a lot of effort. In that case, the predator is more selective.


title: Predation

text: One of the factors to consider is size. Prey that is too small may not be worth the trouble for the amount of energy it provides. Too large, and it may be too difficult to capture. For example, a mantid captures prey with its forelegs and they are optimized for grabbing prey of a certain size. Mantids are reluctant to attack prey that is far from that size. There is a positive correlation between the size of a predator and its prey.


title: Predation

text: A predator may also assess a patch and decide whether to spend time searching for prey in it. This may involve some knowledge of the preferences of the prey; for example, ladybirds can choose a patch of vegetation suitable for their aphid prey.


title: Predation

text: To capture prey, predators have a spectrum of pursuit modes that range from overt chase ("pursuit predation") to a sudden strike on nearby prey ("ambush predation"). Another strategy in between ambush and pursuit is "ballistic interception", where a predator observes and predicts a prey's motion and then launches its attack accordingly.


title: Predation

text: Ambush or sit-and-wait predators are carnivorous animals that capture prey by stealth or surprise. In animals, ambush predation is characterized by the predator's scanning the environment from a concealed position until a prey is spotted, and then rapidly executing a fixed surprise attack. Vertebrate ambush predators include frogs, fish such as the angel shark, the northern pike and the eastern frogfish. Among the many invertebrate ambush predators are trapdoor spiders and Australian Crab spiders on land and mantis shrimps in the sea. Ambush predators often construct a burrow in which to hide, improving concealment at the cost of reducing their field of vision. Some ambush predators also use lures to attract prey within striking range. The capturing movement has to be rapid to trap the prey, given that the attack is not modifiable once launched.


title: Predation

text: Ballistic interception is the strategy where a predator observes the movement of a prey, predicts its motion, works out an interception path, and then attacks the prey on that path. This differs from ambush predation in that the predator adjusts its attack according to how the prey is moving. Ballistic interception involves a brief period for planning, giving the prey an opportunity to escape. Some frogs wait until snakes have begun their strike before jumping, reducing the time available to the snake to recalibrate its attack, and maximising the angular adjustment that the snake would need to make to intercept the frog in real time. Ballistic predators include insects such as dragonflies, and vertebrates such as archerfish (attacking with a jet of water), chameleons (attacking with their tongues), and some colubrid snakes.


title: Predation

text: In pursuit predation, predators chase fleeing prey. If the prey flees in a straight line, capture depends only on the predator's being faster than the prey. If the prey manoeuvres by turning as it flees, the predator must react in real time to calculate and follow a new intercept path, such as by parallel navigation, as it closes on the prey. Many pursuit predators use camouflage to approach the prey as close as possible unobserved ("stalking") before starting the pursuit. Pursuit predators include terrestrial mammals such as humans, African wild dogs, spotted hyenas and wolves; marine predators such as dolphins, orcas and many predatory fishes, such as tuna; predatory birds (raptors) such as falcons; and insects such as dragonflies.


title: Predation

text: An extreme form of pursuit is endurance or persistence hunting, in which the predator tires out the prey by following it over a long distance, sometimes for hours at a time. The method is used by human hunter-gatherers and by canids such as African wild dogs and domestic hounds. The African wild dog is an extreme persistence predator, tiring out individual prey by following them for many miles at relatively low speed.


title: Predation

text: A specialised form of pursuit predation is the lunge feeding of baleen whales. These very large marine predators feed on plankton, especially krill, diving and actively swimming into concentrations of plankton, and then taking a huge gulp of water and filtering it through their feathery baleen plates.


title: Predation

text: Once the predator has captured the prey, it has to handle it: very carefully if the prey is dangerous to eat, such as if it possesses sharp or poisonous spines, as in many prey fish. Some catfish such as the Ictaluridae have spines on the back (dorsal) and belly (pectoral) which lock in the erect position; as the catfish thrashes about when captured, these could pierce the predator's mouth, possibly fatally. Some fish-eating birds like the osprey avoid the danger of spines by tearing up their prey before eating it.


title: Predation

text: In social predation, a group of predators cooperates to kill prey. This makes it possible to kill creatures larger than those they could overpower singly; for example, hyenas, and wolves collaborate to catch and kill herbivores as large as buffalo, and lions even hunt elephants. It can also make prey more readily available through strategies like flushing of prey and herding it into a smaller area. For example, when mixed flocks of birds forage, the birds in front flush out insects that are caught by the birds behind. Spinner dolphins form a circle around a school of fish and move inwards, concentrating the fish by a factor of 200. By hunting socially chimpanzees can catch colobus monkeys that would readily escape an individual hunter, while cooperating Harris hawks can trap rabbits.


title: Predation

text: Predators of different species sometimes cooperate to catch prey. In coral reefs, when fish such as the grouper and coral trout spot prey that is inaccessible to them, they signal to giant moray eels, Napoleon wrasses or octopuses. These predators are able to access small crevices and flush out the prey. Killer whales have been known to help whalers hunt baleen whales.


title: Predation

text: Social hunting allows predators to tackle a wider range of prey, but at the risk of competition for the captured food. Solitary predators have more chance of eating what they catch, at the price of increased expenditure of energy to catch it, and increased risk that the prey will escape. Ambush predators are often solitary to reduce the risk of becoming prey themselves. Of 245 terrestrial members of the Carnivora (the group that includes the cats, dogs, and bears), 177 are solitary; and 35 of the 37 wild cats are solitary, including the cougar and cheetah. However, the solitary cougar does allow other cougars to share in a kill, and the coyote can be either solitary or social. Other solitary predators include the northern pike, wolf spiders and all the thousands of species of solitary wasps among arthropods, and many microorganisms and zooplankton.


title: Predation

text: Under the pressure of natural selection, predators have evolved a variety of physical adaptations for detecting, catching, killing, and digesting prey. These include speed, agility, stealth, sharp senses, claws, teeth, filters, and suitable digestive systems.


title: Predation

text: For detecting prey, predators have well-developed vision, smell, or hearing. Predators as diverse as owls and jumping spiders have forward-facing eyes, providing accurate binocular vision over a relatively narrow field of view, whereas prey animals often have less acute all-round vision. Animals such as foxes can smell their prey even when it is concealed under of snow or earth. Many predators have acute hearing, and some such as echolocating bats hunt exclusively by active or passive use of sound.


title: Predation

text: Predators including big cats, birds of prey, and ants share powerful jaws, sharp teeth, or claws which they use to seize and kill their prey. Some predators such as snakes and fish-eating birds like herons and cormorants swallow their prey whole; some snakes can unhinge their jaws to allow them to swallow large prey, while fish-eating birds have long spear-like beaks that they use to stab and grip fast-moving and slippery prey. Fish and other predators have developed the ability to crush or open the armoured shells of molluscs.


title: Predation

text: Many predators are powerfully built and can catch and kill animals larger than themselves; this applies as much to small predators such as ants and shrews as to big and visibly muscular carnivores like the cougar and lion.


title: Predation

text: Predators are often highly specialized in their diet and hunting behaviour; for example, the Eurasian lynx only hunts small ungulates. Others such as leopards are more opportunistic generalists, preying on at least 100 species. The specialists may be highly adapted to capturing their preferred prey, whereas generalists may be better able to switch to other prey when a preferred target is scarce. When prey have a clumped (uneven) distribution, the optimal strategy for the predator is predicted to be more specialized as the prey are more conspicuous and can be found more quickly; this appears to be correct for predators of immobile prey, but is doubtful with mobile prey.


title: Predation

text: In size-selective predation, predators select prey of a certain size. Large prey may prove troublesome for a predator, while small prey might prove hard to find and in any case provide less of a reward. This has led to a correlation between the size of predators and their prey. Size may also act as a refuge for large prey. For example, adult elephants are relatively safe from predation by lions, but juveniles are vulnerable.


title: Predation

text: Members of the cat family such as the snow leopard (treeless highlands), tiger (grassy plains, reed swamps), ocelot (forest), fishing cat (waterside thickets), and lion (open plains) are camouflaged with coloration and disruptive patterns suiting their habitats.


title: Predation

text: In aggressive mimicry, certain predators, including insects and fishes, make use of coloration and behaviour to attract prey. Female "Photuris" fireflies, for example, copy the light signals of other species, thereby attracting male fireflies, which they capture and eat. Flower mantises are ambush predators; camouflaged as flowers, such as orchids, they attract prey and seize it when it is close enough. Frogfishes are extremely well camouflaged, and actively lure their prey to approach using an esca, a bait on the end of a rod-like appendage on the head, which they wave gently to mimic a small animal, gulping the prey in an extremely rapid movement when it is within range.


title: Predation

text: Many smaller predators such as the box jellyfish use venom to subdue their prey, and venom can also aid in digestion (as is the case for rattlesnakes and some spiders). The marbled sea snake that has adapted to egg predation has atrophied venom glands, and the gene for its three finger toxin contains a mutation (the deletion of two nucleotides) that inactives it. These changes are explained by the fact that its prey does not need to be subdued.


title: Predation

text: Several groups of predatory fish have the ability to detect, track, and sometimes, as in the electric ray, to incapacitate their prey by sensing and generating electric fields. The electric organ is derived from modified nerve or muscle tissue.


title: Predation

text: Physiological adaptations to predation include the ability of predatory bacteria to digest the complex peptidoglycan polymer from the cell walls of the bacteria that they prey upon. Carnivorous vertebrates of all five major classes (fishes, amphibians, reptiles, birds, and mammals) have lower relative rates of sugar to amino acid transport than either herbivores or omnivores, presumably because they acquire plenty of amino acids from the animal proteins in their diet.


title: Predation

text: To counter predation, prey have evolved defences for use at each stage of an attack. They can try to avoid detection, such as by using camouflage and mimicry. They can detect predators and warn others of their presence.


title: Predation

text: If detected, they can try to avoid being the target of an attack, for example, by signalling that they are toxic or unpalatable, by signalling that a chase would be unprofitable, or by forming groups. If they become a target, they can try to fend off the attack with defences such as armour, quills, unpalatability, or mobbing; and they can often escape an attack in progress by startling the predator, playing dead, shedding body parts such as tails, or simply fleeing.


title: Predation

text: Predators and prey are natural enemies, and many of their adaptations seem designed to counter each other. For example, bats have sophisticated echolocation systems to detect insects and other prey, and insects have developed a variety of defences including the ability to hear the echolocation calls. Many pursuit predators that run on land, such as wolves, have evolved long limbs in response to the increased speed of their prey. Their adaptations have been characterized as an evolutionary arms race, an example of the coevolution of two species. In a gene centered view of evolution, the genes of predator and prey can be thought of as competing for the prey's body. However, the "life-dinner" principle of Dawkins and Krebs predicts that this arms race is asymmetric: if a predator fails to catch its prey, it loses its dinner, while if it succeeds, the prey loses its life.


title: Predation

text: The metaphor of an arms race implies ever-escalating advances in attack and defence. However, these adaptations come with a cost; for instance, longer legs have an increased risk of breaking, while the specialized tongue of the chameleon, with its ability to act like a projectile, is useless for lapping water, so the chameleon must drink dew off vegetation.


title: Predation

text: The "life-dinner" principle has been criticized on multiple grounds. The extent of the asymmetry in natural selection depends in part on the heritability of the adaptive traits. Also, if a predator loses enough dinners, it too will lose its life. On the other hand, the fitness cost of a given lost dinner is unpredictable, as the predator may quickly find better prey. In addition, most predators are generalists, which reduces the impact of a given prey adaption on a predator. Since specialization is caused by predator-prey coevolution, the rarity of specialists may imply that predator-prey arms races are rare.


title: Predation

text: It is difficult to determine whether given adaptations are truly the result of coevolution, where a prey adaptation gives rise to a predator adaptation that is countered by further adaptation in the prey. An alternative explanation is "escalation", where predators are adapting to competitors, their own predators or dangerous prey. Apparent adaptations to predation may also have arisen for other reasons and then been co-opted for attack or defence. In some of the insects preyed on by bats, hearing evolved before bats appeared and was used to hear signals used for territorial defence and mating. Their hearing evolved in response to bat predation, but the only clear example of reciprocal adaptation in bats is stealth echolocation.


title: Predation

text: A more symmetric arms race may occur when the prey are dangerous, having spines, quills, toxins or venom that can harm the predator. The predator can respond with avoidance, which in turn drives the evolution of mimicry. Avoidance is not necessarily an evolutionary response as it is generally learned from bad experiences with prey. However, when the prey is capable of killing the predator (as can a coral snake with its venom), there is no opportunity for learning and avoidance must be inherited. Predators can also respond to dangerous prey with counter-adaptations. In western North America, the common garter snake has developed a resistance to the toxin in the skin of the rough-skinned newt.


title: Predation

text: Predators affect their ecosystems not only directly by eating their own prey, but by indirect means such as reducing predation by other species, or altering the foraging behaviour of a herbivore, as with the biodiversity effect of wolves on riverside vegetation or sea otters on kelp forests. This may explain population dynamics effects such as the cycles observed in lynx and snowshoe hares.


title: Predation

text: One way of classifying predators is by trophic level. Carnivores that feed on herbivores are secondary consumers; their predators are tertiary consumers, and so forth. At the top of this food chain are apex predators such as lions. Many predators however eat from multiple levels of the food chain; a carnivore may eat both secondary and tertiary consumers. This means that many predators must contend with intraguild predation, where other predators kill and eat them. For example, coyotes compete with and sometimes kill gray foxes and bobcats.


title: Predation

text: Predators may increase the biodiversity of communities by preventing a single species from becoming dominant. Such predators are known as keystone species and may have a profound influence on the balance of organisms in a particular ecosystem. Introduction or removal of this predator, or changes in its population density, can have drastic cascading effects on the equilibrium of many other populations in the ecosystem. For example, grazers of a grassland may prevent a single dominant species from taking over.


title: Predation

text: The elimination of wolves from Yellowstone National Park had profound impacts on the trophic pyramid. In that area, wolves are both keystone species and apex predators. Without predation, herbivores began to over-graze many woody browse species, affecting the area's plant populations. In addition, wolves often kept animals from grazing near streams, protecting the beavers' food sources. The removal of wolves had a direct effect on the beaver population, as their habitat became territory for grazing. Increased browsing on willows and conifers along Blacktail Creek due to a lack of predation caused channel incision because the reduced beaver population was no longer able to slow the water down and keep the soil in place. The predators were thus demonstrated to be of vital importance in the ecosystem.


title: Predation

text: In the absence of predators, the population of a species can grow exponentially until it approaches the carrying capacity of the environment. Predators limit the growth of prey both by consuming them and by changing their behavior. Increases or decreases in the prey population can also lead to increases or decreases in the number of predators, for example, through an increase in the number of young they bear.


title: Predation

text: Cyclical fluctuations have been seen in populations of predator and prey, often with offsets between the predator and prey cycles. A well-known example is that of the snowshoe hare and lynx. Over a broad span of boreal forests in Alaska and Canada, the hare populations fluctuate in near synchrony with a 10-year period, and the lynx populations fluctuate in response. This was first seen in historical records of animals caught by fur hunters for the Hudson Bay Company over more than a century.


title: Predation

text: A simple model of a system with one species each of predator and prey, the Lotka–Volterra equations, predicts population cycles. However, attempts to reproduce the predictions of this model in the laboratory have often failed; for example, when the protozoan "Didinium nasutum" is added to a culture containing its prey, "Paramecium caudatum", the latter is often driven to extinction.


title: Predation

text: The Lotka-Volterra equations rely on several simplifying assumptions, and they are structurally unstable, meaning that any change in the equations can stabilize or destabilize the dynamics. For example, one assumption is that predators have a linear functional response to prey: the rate of kills increases in proportion to the rate of encounters. If this rate is limited by time spent handling each catch, then prey populations can reach densities above which predators cannot control them. Another assumption is that all prey individuals are identical. In reality, predators tend to select young, weak, and ill individuals, leaving prey populations able to regrow.


title: Predation

text: Many factors can stabilize predator and prey populations. One example is the presence of multiple predators, particularly generalists that are attracted to a given prey species if it is abundant and look elsewhere if it is not. As a result, population cycles tend to be found in northern temperate and subarctic ecosystems because the food webs are simpler. The snowshoe hare-lynx system is subarctic, but even this involves other predators, including coyotes, goshawks and great horned owls, and the cycle is reinforced by variations in the food available to the hares.