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White-winged triller
The White-winged Triller (Lalage tricolor) is one of the smaller members of the Cuckoo-shrike family, Campephagidae. It is found throughout mainland Australia and possibly on the islands to the north, including New Guinea and eastern Indonesia. It is resident or nomadic over the warmer part of its range (inland Australia and points north), and a summer breeding migrant to the cooler southern parts of Australia.
White-winged Trillers are fairly common in woodland, and open scrub through most of their range, and close to riverbeds in the central arid zone. The conspicuous male bird—black above and white below in breeding plumage—trills cheerfully through much of the day during the breeding season (mid-spring to early summer), frequently rising on fluttering wings in song flight.
The female is similarly patterned but in dull fawns and white. In the non-breeding season, male birds appear similar to the female, retaining blackish feathers only on the wings and tail.
Typically 16 to 18 cm long, White-winged Trillers eat a variety of insects, which are taken on the ground, from in foliage, or in the air.
The correct classification of the White-winged Triller and its close northern relative, the White-shouldered Triller (Lalage sueurii) of Eastern Indonesia is uncertain. Some authorities regard them as two races of a single species, in which case the White-winged Triller becomes Lalage sueurii tricolor.
Category:Campephagidae
Cuckoo-shrike
- Coracina
- Campochaera
- Lalage
- Campephaga
- Pericrocotus
- Hemipus
The cuckoo-shrikes are small to medium-sized passerine bird species found in the subtropical and tropical Africa, Asia and Australasia.
They are mainly greyish and resemble cuckoos or shrikes, although they are not closely related to either. The minivets are, however brightly coloured in red, yellow and blacks.
These are mainly insectivorous forest birds. About four blotchy white, green or blue eggs are laid in a cup nest in a tree. Incubation is about two weeks.
Species of Campephagidae
- Ground Cuckoo-shrike, Coracina maxima
- Large Cuckoo-shrike, Coracina macei
- Sunda Cuckoo-shrike, Coracina larvata
- Javan Cuckoo-shrike, Coracina javensis
- Slaty Cuckoo-shrike, Coracina schistacea
- Wallacean Cuckoo-shrike, Coracina personata
- Melanesian Cuckoo-shrike, Coracina caledonica
- Black-faced Cuckoo-shrike, Coracina novaehollandiae
- Stout-billed Cuckoo-shrike, Coracina caeruleogrisea
- Bar-bellied Cuckoo-shrike, Coracina striata
- Pied Cuckoo-shrike, Coracina bicolor
- Moluccan Cuckoo-shrike, Coracina atriceps
- Buru Cuckoo-shrike, Coracina fortis
- Cerulean Cuckoo-shrike, Coracina temminckii
- Yellow-eyed Cuckoo-shrike, Coracina lineata
- Boyer's Cuckoo-shrike, Coracina boyeri
- White-rumped Cuckoo-shrike, Coracina leucopygia
- White-bellied Cuckoo-shrike, Coracina papuensis
- Hooded Cuckoo-shrike, Coracina longicauda
- Halmahera Cuckoo-shrike, Coracina parvula
- Pygmy Cuckoo-shrike, Coracina abbotti
- New Caledonian Cuckoo-shrike, Coracina analis
- White-breasted Cuckoo-shrike, Coracina pectoralis
- Blue Cuckoo-shrike, Coracina azurea
- Gray Cuckoo-shrike, Coracina caesia
- Grauer's Cuckoo-shrike, Coracina graueri
- Ashy Cuckoo-shrike, Coracina cinerea
- Mauritius Cuckoo-shrike, Coracina typica
- Reunion Cuckoo-shrike, Coracina newtoni
- Cicadabird, Coracina tenuirostris
- Blackish Cuckoo-shrike, Coracina coerulescens
- Sumba Cuckoo-shrike, Coracina dohertyi
- Sula Cuckoo-shrike, Coracina sula
- Kai Cuckoo-shrike, Coracina dispar
- Black-bibbed Cuckoo-shrike, Coracina mindanensis
- Sulawesi Cuckoo-shrike, Coracina morio
- Pale-grey Cuckoo-shrike, Coracina ceramensis
- Papuan Cuckoo-shrike, Coracina incerta
- Gray-headed Cuckoo-shrike, Coracina schisticeps
- New Guinea Cuckoo-shrike, Coracina melas
- Black-bellied Cuckoo-shrike, Coracina montana
- Solomon Islands Cuckoo-shrike, oracina holopolia
- McGregor's Cuckoo-shrike, Coracina mcgregori
- Indochinese Cuckoo-shrike, Coracina polioptera
- White-winged Cuckoo-shrike, Coracina ostenta
- Black-winged Cuckoo-shrike, Coracina melaschistos
- Lesser Cuckoo-shrike, Coracina fimbriata
- Black-headed Cuckoo-shrike, Coracina melanoptera
- Golden Cuckoo-shrike, Campochaera sloetii
- Black-and-white Triller, Lalage melanoleuca
- Pied Triller, Lalage nigra
- White-rumped Triller, Lalage leucopygialis
- White-shouldered Triller, Lalage sueurii
- White-winged Triller, Lalage tricolor
- Rufous-bellied Triller, Lalage aurea
- White-browed Triller, Lalage moesta
- Varied Triller, Lalage leucomela
- Black-browed Triller, Lalage atrovirens
- Samoan Triller, Lalage sharpei
- Polynesian Triller, Lalage maculosa
- Long-tailed Triller, Lalage leucopyga
- Petit's Cuckoo-shrike, Campephaga petiti
- Black Cuckoo-shrike, Campephaga flava
- Red-shouldered Cuckoo-shrike, Campephaga phoenicea
- Purple-throated Cuckoo-shrike, Campephaga quiscalina
- Ghana Cuckoo-shrike, Campephaga lobata
- Oriole Cuckoo-shrike, Campephaga oriolina
- Rosy Minivet, Pericrocotus roseus
- Brown-rumped Minivet, Pericrocotus cantonensis
- Ashy Minivet, Pericrocotus divaricatus
- Small Minivet, Pericrocotus cinnamomeus
- Ryukyu Minivet,Pericrocotus tegimae
- Fiery Minivet, Pericrocotus igneus
- Flores Minivet, Pericrocotus lansbergei
- White-bellied Minivet, Pericrocotus erythropygius
- Long-tailed Minivet, Pericrocotus ethologus
- Short-billed Minivet, Pericrocotus brevirostris
- Sunda Minivet, Pericrocotus miniatus
- Scarlet Minivet, Pericrocotus flammeus
- Gray-chinned Minivet, Pericrocotus solaris
- Bar-winged Flycatcher-shrike, Hemipus picatus
- Black-winged Flycatcher-shrike, Hemipus hirundinaceus
-
New Guinearight
New Guinea, located just north of Australia, is the world's second largest island having become separated from the Australian mainland when the area now known as the Torres Strait flooded around 5000 BC. The name papua has also been long-associated with the island: this is discussed further under History, below.
Political divisions
The island is divided politically along east-west lines, roughly into equal halves:
- The portions of the island of New Guinea (Irian in Bahasa Indonesia) located west of 141°E longitude (see [http://www.papuaweb.org/goi/pp/peta-hr.gif map]) are incorporated into Indonesia as the provinces:
- West Irian Jaya (Irian Jaya Barat) with Manokwari as its capital
- Papua (formerly Irian Jaya) with the city of Jayapura as its capital. A proposal to split this into Central Papua (Papua Tengah) and East Papua (Papua Timur) has not been implemented.Jayapura]
:Papuans actively have supported a broad-based independence movement, the Organisasi Papua Merdeka or OPM, against Indonesia since 1962. Its military arm is the TPN, or the Liberation Army of Free Papua. The Indonesian authorities view this as a separatist and a terrorist movement, the members of which are guilty of high treason. The OPM has charged the Indonesian government with racism, genocide, political assassination, torture and terrorism. Amnesty International has estimated more than 100,000 Papuans have died as a result of government-sponsored violence against Papuans, while others have set the number at more than 200,000.
- The eastern part forms the primary part of the nation of Papua New Guinea, which has been an independent country since 1975.
People
Populated by very nearly a thousand different Papua Melanesian tribal groups since 45,000 BC, New Guinea is the home of the world's oldest independent societies and a staggering number of separate languages, the Papuan languages. The separation was not merely linguistic; warfare among societies was a factor in the evolution of the men's house: separate housing of groups of adult men, from the single-family houses of the women and children, for mutual protection against the other groups. Pig-based trade between the groups and pig-based feasts are a common theme with the other peoples of Southeast Asia and Oceania. Most societies practice agriculture, supplemented by hunting and gathering.
The island's population is comprised of roughly two indigenous ethnic groups: Papuans and Austronesians. Current evidence (archaeological, linguistic and biological) indicates that the Papuans are the oldest human residents of New Guinea, and that they constitute the majority of the population of New Guinea. Austronesians are a group who originated in Taiwan and spread from there through the Philippines and Indonesia and on into the Pacific. These seafaring peoples reached New Guinea many thousands of years after the arrival of the Papuans. They have colonised many offshore islands in the north and east of New Guinea, and in some places have settled on the mainland. The many thousands of years of human occupation of New Guinea has led to a great deal of ethnic diversity, which has been increased by the arrival of the Austronesians and the more recent history of European and Asian colonization. The Indonesian government which controls the western half of New Guinea has instituted an aggressive transmigration program designed to bring chiefly Sumatran and Javanese immigrants to Indonesian New Guinea to tip the largely black population toward a more Asian "balance." To date, more than 1 million Asian immigrants have settled in western New Guinea as part of the transmigration program.
Ecology
With some 786,000 km² of tropical land, New Guinea has an immense ecological value: 11,000 plant species; nearly 600 unique bird species, including the birds of paradise, cassowaries; over 400 amphibians; 455 butterfly species; marsupials including bondegezou, Goodfellow's tree kangaroo, Huon tree kangaroo, long-beaked echidna, tenkile, agile wallaby, alpine wallaby, cuscus and possums; and various other mammal species. Most of these species are shared, at least in their origin, with the continent of Australia, which was until fairly recent geological times, part of the same landmass. See Australia-New Guinea for an overview.
History
See also: History of Papua New Guinea
The first inhabitants of New Guinea arrived at least 60,000 years ago, having travelled through the south-east Asian peninsula. These first inhabitants, from whom the Papuan people are probably descended, adapted to the range of ecologies and in time developed one of the earliest known agricultures. Remains of this agricultural system, in the form of ancient irrigation systems in the highlands of Papua New Guinea, are being studied by archaeologists. This work is still in its early stages so there is still uncertainty as to precisely what crop was being grown, or when/where agriculture arose.
The gardens of the New Guinea highlands are ancient, intensive permacultures, adapted to high population densities, very high rainfalls (as high as 10,000 mm/yr (400 in/yr)), earthquakes, hilly land, and occasional frost. Complex mulches, crop rotations and tillages are used in rotation on terraces with complex irrigation systems. Western agronomists still do not understand all practices, and native gardeners are notably more successful than most scientific farmers. Some authorities believe that New Guinea gardeners invented crop rotation well before western europeans. A unique feature of New Guinea permaculture is the silviculture of Casuarina oligodon, a tall, sturdy native ironwood tree, suited to use for timber and fuel, with root nodules that fix nitrogen. Pollen studies show that it was adopted during an ancient period of extreme deforestation.
In more recent millennia another wave of people arrived on the shores of New Guinea. These were the Austronesian people, who had spread down from Taiwan, through the south-east Asian archipelago, colonising many of the islands on the way. The Austronesian people had technology and skills extremely well adapted to ocean voyaging and Austronesian language speaking people are present along much of the coastal areas and islands of New Guinea.
The first European contact with New Guinea was by Portuguese and/or Spanish sailors in the 16th century. In 1526-27 Don Jorge de Meneses saw the western tip of New Guinea and named it ilhas dos Papuas. The word papua is often said to derive from the Malay word papua or pua-pua, meaning ‘frizzly-haired’, referring to the frizzled hair of the inhabitants of these areas. Another possibility, (put forward by Sollewijn Gelpke in 1993) is that it comes from the Biak phrase sup i papwa which means ‘the land below [the sunset]’ and refers to the islands west of the Bird’s Head, as far as Halmahera.
Whatever the origin of the name Papua, it came to be associated with this area, and more especially with Halmahera, which was known to the Portuguese by this name during the era of their colonisation in this part of the world.
In 1545 the Spaniard Yñigo Ortiz de Retez sailed along the north coast of New Guinea as far as the Mamberamo River near which he landed, naming the island 'Nueva Guinea'. The first map showing the whole island (as an island) was published in 1600 and shows it as 'Nova Guinea'.
The first European claim occurred in 1828, when the Netherlands formally claimed the western half of the island. In 1883, following a short-lived French annexation of New Ireland, the British colony of Queensland annexed south-eastern New Guinea. However, the Queensland government's superiors in the United Kingdom revoked the claim, and (formally) assumed direct responsibility in 1884, when Germany claimed north-eastern New Guinea as a protectorate. The first Dutch government posts were established in 1898 and in 1902 Manokwari on the North coast, Fak-Fak in the West and Merauke in the South at the border with British New Guinea (later renamed Papua).
Both the Dutch and the British tried to suppress warfare and headhunting once common between the villages of the populace.
In 1906 the British government transferred total responsibility for south-east New Guinea to Australia. During World War I, Australian forces seized German New Guinea, which in 1920 became a League of Nations mandated territory of Australia. The Australian territories became collectively known as The Territories of Papua and New Guinea (until February 1942).
Before about 1930, most European maps showed the highlands as uninhabited forests. When first flown over by aircraft, numerous settlements with agricultural terraces and stockades were observed.
Netherlands New Guinea and the Australian territories were invaded in 1942 by the Japanese. The Australian territories were put under military administration and were known simply as New Guinea. The highlands, northern and eastern parts of the island became key battlefields in the South West Pacific Theatre of World War II. Papuans often gave vital assistance to the Allies, fighting alongside Australian and US troops, and carrying equipment and injured men across New Guinea. Following the return to civil administration, the Australian section was known as the Territory of Papua-New Guinea (1945-49) and then as Papua and New Guinea. Although the rest of the Dutch East Indies achieved independence as Indonesia on December 27, 1949, the Netherlands regained control of western New Guinea.
During the 1950s the Dutch government began to prepare Netherlands New Guinea for full independence and allowed elections in 1959; an elected Papuan Council, the New Guinea Council (Nieuw Guinea Raad) took office on April 5, 1961. The Council decided on the name of West Papua, a national emblem, a flag called the Morning Star or Bintang Kejora, and a national anthem; the flag was first raised — next to the Dutch flag — on December 1, 1961. However, Indonesia threatened with an invasion, after full mobilisation of its army, by August 15, 1962. It had received with military help from the Soviet Union. Under strong pressure of the Kennedy administration the Dutch, who were prepared to resist an Indonesian attack, had to go to the conference table. On October 1, 1962, the Dutch handed over the territory to a temporary UN administration (UNTEA). On May 1, 1963, Indonesia took control. The territory was renamed West Irian and then Irian Jaya. In 1969 Indonesia, under the 1962 New York Agreement, had to organize a plebiscite to seek the consent of the Papuans for Indonesian rule. This so called Act of Free Choice (Pepera) resulted under strong threats and intimidations of the Indonesian army in a 100% vote for continued Indonesian rule.
From 1971, the name Papua New Guinea was used for the Australian territory. In 1975, Australia granted full independence to Papua New Guinea.
In 2000, amid increasing discontent and opposition to Indonesian rule, Irian Jaya was formally renamed "The Province of Papua" and a large measure of "special autonomy" was granted in 2001. This law on special autonomy, however, was never implemented. On the contrary, beginning of 2003 President Megawati Sukarnoputri announced the division of the province into three parts, while the name "Papua" for the province would again revert to Irian. With strong public protest by Papuans only the province of West Irian Jaya, with Manokwari as its capital, covering the Bird's Head peninsula was split from Papua Province. In 2005 a new proposal came from Jakarta to split the province into five provinces, with the clear purpose to eliminate all anti-Indonesian and pro-independence action.
External links
- [http://natzoo.si.edu/Publications/ZooGoer/2001/2/intoxnewguineabirds.cfm The Intoxicating Birds of New Guinea by John Tidwell]
- [http://www.fpcn-global.org/index.php?module=htmlpages&func=display&pid=1 Online documentaries re OPM sponsored by West German-based Friends of Peoples Close to Nature]
- [http://www.papuaweb.org/gb/peta/sejarah/collingridge/ Facsimile of material from "The Discovery of New Guinea" by George Collingridge]
Category:Islands
Category:Melanesia
Category:New Guinea
zh-min-nan:Sin Guinea
ko:뉴기니 섬
ja:ニューギニア島
Bird migrationLong-distance land bird migration
Many species of land birds migrate very long distances, the most common pattern being for birds to breed in the temperate or arctic northern hemisphere and winter in warmer regions, often in the tropics or the southern hemisphere.
There is a strong genetic component to migration in terms of timing and route, but this may be modified by environmental influences. An interesting example where a change of migration route has occurred because of such a geographical barrier is the trend for some Blackcaps in central Europe to migrate west and winter in Britain rather than cross the Alps.
The advantage of the migration strategy is that, in the long days of the northern summer, breeding birds have more hours to feed their young on often abundant food supplies, particularly insects. As the days shorten in autumn and food supplies become scarce, the birds can return to warmer regions where the length of the day varies less and there is an all year round food supply.
The downside of migration is the hazards of the journey, especially when difficult habitats such as deserts and oceans must be crossed, and weather conditions may be adverse.
The risks of predation are also high. The Eleonora's Falcon which breeds on Mediterranean islands has a very late breeding season, timed so that autumn passerine migrants can be hunted to feed its young.
Whether a particular species migrates depends on a number of factors. The climate of the breeding area is important, and few species can cope with the harsh winters of inland Canada or northern Eurasia. Thus the Blackbird Turdus merula is migratory in Scandinavia, but not in the milder climate of southern Europe.
The nature of the staple food is also important. Most specialist insect eaters are long-distance migrants, and have little choice but to head south in winter.
Certain areas, because of their location, have become famous as watchpoints for migrating birds. Examples are the Point Pelee National Park in Canada, and Spurn in England. Drift migration of birds blown off course by the wind can result in "falls" of large numbers of migrants at coastal sites.
Another cause of birds occurring outside their normal ranges is the "spring overshoot" in which birds returning to their breeding areas overshoot and end up further north than intended.
A mechanism which can lead to great rarities turning up as vagrants thousands of kilometres out of range is reverse migration, where the genetic programming of young birds fails to work properly.
Recent research suggests that long-distance passerine migrants are of South American and African, rather than northern hemisphere, evolutionary origins. They are effectively southern species coming north to breed rather than northern species going south to winter.
Broad-winged long distance migrants
Some large broad-winged birds rely on thermal columns of rising hot air to enable them to soar. These include many birds of prey such as vultures, eagles and buzzards, but also storks.
Migratory species in these groups have great difficulty crossing large bodies of water, since thermals can only form over land, and these birds cannot maintain active flight for long distances.
The Mediterranean and other seas therefore present a major obstacle to soaring birds, which are forced to cross at the narrowest points. This means that massive numbers of large raptors and storks pass through areas such as Gibraltar, Falsterbo and the Bosphorus at migration times. Commoner species, such as the Honey Buzzard, can be counted in hundreds of thousands in autumn.
Other barriers, such as mountain ranges, can also cause funnelling, particularly of large diurnal migrants.
Short-distance land bird migration
The long-distance migrants in the previous section are effectively genetically programmed to respond to changing lengths of days. However many species move shorter distances, but may do so only in response to harsh weather conditions.
Thus mountain and moorland breeders, such as Wallcreeper and White-throated Dipper, may move only altitudinally to escape the cold higher ground. Other species such as Merlin and Skylark will move further to the coast or to a more southerly region.
Species like the Chaffinch are not migratory in Britain, but will move south or to Ireland in very cold weather. Interestingly, in Scandinavia, the female of this species migrates, but not the male, giving rise to the specific name coelebs, a bachelor.
Short-distance passerine migrants have two evolutionary origins. Those which have long-distance migrants in the same family, such as the Chiffchaff, are species of southern hemisphere origins which have progressively shortened their return migration so that they stay in the northern hemisphere.
Those species which have no long-distance migratory relatives, such as the waxwings, are effectively moving in response to winter weather, rather than enhanced breeding opportunities.
Wildfowl and waders
The typical image of migration is of northern landbirds such as swallows and birds of prey making long flights to the tropics. Many northern-breeding ducks, geese and swans are also long-distance migrants, but need only to move from their arctic breeding grounds far enough south to escape frozen waters.
This means that most wildfowl remain in the Northern hemisphere, but in milder countries. For example, the Pink-footed Goose migrates from Iceland to Britain and neighbouring countries. Usually wintering grounds are traditional and learned by the young when they migrate with their parents.
Some ducks, such as the Garganey, do move completely or partially into the tropics.
A similar situation occurs with waders (called "shorebirds" in North America). Many species, such as Dunlin and Western Sandpiper, undertake long movements from their arctic breeding grounds to warmer locations in the same hemisphere, but others such as Semipalmated Sandpiper travel huge distances to the tropics.
Most of the wildfowl are large and powerful, and even the waders are strong fliers. This means that birds wintering in temperate regions have the capacity to make further shorter movements in the event of particularly inclement weather.
The same considerations about barriers and detours that apply to long-distance land-bird migration apply to water birds, but in reverse: a large area of land without bodies of water that offer feeding sites is a barrier to a water bird. Open sea may also be a barrier to a bird that feeds in coastal waters. Detours avoiding such barriers are observed: for example, Brent Geese migrating from the Taymyr Peninsula to the Wadden Sea travel via the White Sea coast and the Baltic Sea rather than directly across the Arctic Ocean and northern Scandinavia.
For some species of waders, migration success depends on the availability of certain key food resources at stopover points along the migration route. This gives the migrants an opportunity to "refuel" for the next leg of the voyage. Some examples of important stopover locations are the Bay of Fundy and Delaware Bay.
Some Alaskan Bar-tailed Godwits have the longest non-stop flight of any migrant, flying 11,000 km to their New Zealand wintering grounds (BTO News 258: 3, 2005). Prior to migration, 55% of their bodyweight is stored fat to fuel this uninterrupted journey.
Seabirds
New Zealand
Much of what has been said in the previous section applies to many seabirds. Some, such as the Black Guillemot and some gulls, are quite sedentary; others, such as most of the terns and auks breeding in the temperate northern hemisphere, move south varying distances in winter. The Arctic Tern has the longest-distance migration of any bird, and sees more daylight than any other, moving from its arctic breeding grounds to the antarctic wintering areas. One Arctic Tern, ringed (banded) as a chick on the Farne Islands off the British east coast, reached Melbourne, Australia in just three months from fledging, a sea journey of over 22,000 km (14,000 miles). Seabirds, of course, have the advantage that they can feed on migration.
The most pelagic species, mainly in the 'tubenose' order Procellariiformes, are great wanderers, and the albatrosses of the southern oceans may circle the globe as they ride the "roaring forties" outside the breeding season. The tubenoses in general spread thinly over large areas of open ocean, but congregate when food becomes available. Many of them are also among the longest-distance migrants; Sooty Shearwaters nesting on the Falkland Islands migrate 14,000 km (9,000 miles) between the breeding colony and the North Atlantic Ocean off Norway, and some Manx Shearwaters do the same journey in reverse. As they are long-lived birds, they may cover enormous distances during their lives; one record-breaking Manx Shearwater is calculated to have flown 8 million km (5 million miles) during its over-50 year lifespan.
Pelagic birding trips attract petrels and other procellarids by tipping "chum", a mixture of fish oil and offal, into the sea. Within minutes, a previously apparently empty ocean is full of petrels, fulmars and shearwaters attracted by the food.
A few seabirds, such as Wilson's Petrel and Great Shearwater, breed in the southern hemisphere and migrate north in the southern winter.
The tropics
In the tropics there is little variation in the length of day throughout the year, and it is always warm enough for an adequate food supply. Apart from the seasonal movements of northern hemisphere wintering species, most species are in the broadest sense resident. However many species undergo movements of varying distances depending on the rainfall.
Many tropical regions have wet and dry seasons, the monsoons of India being perhaps the best known example. An example of a bird whose distribution is rain associated is the Woodland Kingfisher of west Africa.
There are a few species, notably cuckoos, which are genuine long-distance migrants within the tropics. An example is the Lesser Cuckoo, which breeds in India and winters in Africa.
In the high mountains, such as the Himalayas and the Andes, there are of course also altitudinal movements of greater or lesser extent by many species.
Australasia
Bird migration is primarily, but not entirely, a Northern-Hemisphere phenomenon. In the Southern Hemisphere, seasonal migration tends to be much less marked. There are several reasons for this.
First, the largely uninterrupted expanses of land mass or ocean tend not to funnel migrations into narrow and obvious pathways, making them less obvious to the human observer. Second, at least for terrestrial birds, climatic regions tend to fade into one another over a long distance rather than be entirely separate: this means that rather than make long trips over unsuitable habitat to reach particular destinations, migrant species can usually travel at a relaxed pace, feeding as they go. Short of banding studies it is often not obvious that the birds seen in any particular locality as the seasons change are in fact different members of the same species passing through, gradually working their way north or south.
Relatively few Australasian birds migrate in the way that so many European and North American species do. This is largely a matter of geography: the Australasian climate has seasonal extremes no less compelling than those of Europe; however, they are far less predictable and tend to take place over periods both shorter and longer. A couple of weeks of heavy rain in one part or another of the usually dry centre of Australia, for example, produces dramatic plant and invertebrate growth, attracting birds from all directions. This can happen at any time of year, summer or winter and, in any given area, may not happen again for a decade or more.
Broader climatic extremes are highly unpredictable also: expected seasonal heat or rain arrives or does not arrive, depending on the vagaries of El Niño. It is commonplace to have stretches of five or ten years at a time when winter rains do not eventuate during the El Niño cycle, and equally common to have La Niña periods which turn arid zones into areas of lush grass and shallow lakes. Long distance migration requires a heavy investment in time and body mass—and, given the random nature of El Niño, an investment with an uncertain return.
In broad terms, Australasian birds tend to be sedentary or nomadic, moving on whenever conditions become unfavourable to whichever area happens to be more suitable at the time.
There are many exceptions, however. Some species make the long haul to breed in far distant northern climes every year, notably swifts, and a great many wading birds that breed in the Arctic Circle during the southern winter.
Many others arrive for the southern spring and summer to breed, then fly to tropical northern Australia, New Guinea, or the islands of South East Asia for the Southern winter. Examples include cuckoos, the Satin Flycatcher, the Dollarbird, and the Rainbow Bee-eater.
Others again are altitudinal migrants, moving to higher country during summer, returning to warmer areas in winter such as several robins, or travel north and south with the seasons but within a relatively restricted range. The tiny 10 cm Silvereye is an example: most of the southernmost Tasmanian race crosses the 200 miles of Bass Strait after breeding to disperse into Victoria, South Australia, New South Wales and even southern Queensland, replacing the normal residents who fly still further north, following the band of fertile country along the coast, feeding through the day and travelling mostly at night. The northernmost populations, however, are nomadic rather than migratory, as are the Silvereyes of southern Western Australia, which is bounded by thousands of miles of desert to the north and east, and sea to the south and west.
Study techniques
Bird migration has been studied by a variety of techniques of which ringing has been the oldest. Color marking, use of radar, satellite tracking and use of stable hydrogen isotopes include some of the newer techniques being used to study the migration of birds.
See also
- Bird ringing
References
- Alerstam, T. (2001). Detours in bird migration. Journal of Theoretical Biology, 209, 319-331.
- Weidensaul, Scott. Living On the Wind: Across the Hemisphere With Migratory Birds. Douglas & McIntyre, 1999.
- Dingle, Hugh. Migration: The Biology of Life on The Move. Oxford Univ. Press, 1996.
External links
- [http://www.trektellen.nl/default.asp?taal=2 Migration counts and ringing records The Netherlands, Belgium, Great Britain and France]
Category:Ornithology
Category:Migratory birds (Eastern hemisphere)
Category:Migratory birds (Western hemisphere)
ko:ì² ìƒˆ
ja:渡り鳥
SpeciesIn biology, a species is the basic unit of biodiversity. In scientific classification, a species is assigned a two-part name in Latin. The genus is listed first (and capitalized), followed by a specific epithet. For example, humans belong to the genus Homo, and are in the species Homo sapiens. The name of the species is the whole binomial not just the second term (the specific epithet). The binomial, and most other purely formal aspects of the biological codes of nomenclature, were formalized by Carolus Linnaeus in the 1700's and as a result are called the "Linnaean system". At that time, species were thought to represent independent acts of creation by God, and were therefore considered objectively real and immutable.
Since the advent of the theory of evolution, the conception of species has undergone vast changes in biology, however no consensus on the definition of the word has yet been reached. The most commonly cited definition of "species" was first coined by Ernst Mayr. By this definition, called the biological species concept or isolation species concept, species are "groups of actually or potentially interbreeding natural populations which are reproductively isolated from other such groups". However, many other species concepts are also used (see other definitions of species below).
The scientific name of a species is properly typeset in italics. When an unknown species is being referred to this may be done by using the abbreviation "sp." in the singular or "spp." in the plural in the place of the second part of the scientific name. Note that the word "specie" is not the singular of "species". It refers to coined money.
Definitions of species
The definition of a species given above as taken from Mayr, is somewhat idealistic. Since it assumes sexual reproduction, it leaves the term undefined for a large class of organisms that reproduce asexually. Biologists frequently do not know whether two morphologically similar groups of organisms are "potentially" capable of interbreeding. Further, there is considerable variation in the degree to which hybridization may succeed under natural and experimental conditions, or even in the degree to which some organisms use sexual reproduction between individuals to breed. Consequently, several lines of thought in the definition of species exist:
; Typological species : A group of organisms in which individuals are members of the species if they sufficiently conform to certain fixed properties. The clusters of variations or phenotypes within specimens (ie: longer and shorter tails) would differentiate the species. This method was used as a "classical" method of determining species, such as with Linnaeus early in evolutionary theory. However, we now know that different phenotypes do not always constitute different species (e.g.: a 4-winged Drosophila born to a 2-winged mother is not a different species). Species named in this manner are called morphospecies.
; Morphological species : A population or group of populations that differs morphologically from other populations. For example, we can distinguish between a chicken and a duck because they have different shaped bills and the duck has webbed feet. Species have been defined in this way since well before the beginning of recorded history. This species concept is much criticised because more recent genetic data reveals that genetically distinct populations may look very similar and, contrarily, large morphological differences sometimes exist between very closely-related populations. Nonetheless, most species known have been described solely from morphology.
; Biological / Isolation species : A set of actually or potentially interbreeding populations. This is generally the most useful formulation for scientists working with living examples of the higher taxa like mammals, fish, and birds, but meaningless for organisms that do not reproduce sexually. It does not distinguish between the theoretical possibility of interbreeding and the actual likelihood of gene flow between populations and is thus impractical in instances of allopatric (geographically isolated) populations. The results of breeding experiments done in artificial conditions may or may not reflect what would happen if the same organisms encountered each other in the wild, making it difficult to gauge whether or not the results of such experiments are meaningful in reference to natural populations.
; Mate-recognition species : A group of organisms that are known to recognise one another as potential mates. Like the isolation species concept above, it applies only to organisms that reproduce sexually. Unlike the isolation species concept, it focuses specifically on pre-mating reproductive isolation.
; Phylogenetic / Evolutionary / Darwinian species : A group of organisms that shares an ancestor; a lineage that maintains its integrity with respect to other lineages through both time and space. At some point in the progress of such a group, members may diverge from one another: when such a divergence becomes sufficiently clear, the two populations are regarded as separate species.
; Microspecies : Species that reproduce without meiosis or mitosis so that each generation is genetically identical to the previous generation. See also apomixis.
In practice, these definitions often coincide, and the differences between them are more a matter of emphasis than of outright contradiction. Nevertheless, no species concept yet proposed is entirely objective, or can be applied in all cases without resorting to judgement. Given the complexity of life, some have argued that such an objective definition is in all likelihood impossible, and biologists should settle for the most practical definition. For most vertebrates, this is the biological species concept, and to a lesser extent (or for different purposes) the phylogenetic species concept. Many BSC subspecies are considered species under the PSC; the difference between the BSC and the PSC can be summed up insofar as that the BSC defines a species as a consequence of manifest evolutionary history, while the PSC defines a species as a consequence of manifest evolutionary potential. Thus, a PSC species is "made" as soon as an evolutionary lineage has started to separate, while a BSC species starts to exist only when the lineage separation is complete.
Importance in biological classification
The idea of species has a long history. It is one of the most important levels of classification, for several reasons:
- It often corresponds to what lay people treat as the different basic kinds of organism - dogs are one species, cats another.
- It is the standard binomial nomenclature (or trinomial nomenclature) by which scientists typically refer to organisms.
- It is the only taxonomic level which has empirical content, in the sense that asserting that two animals are of different species is saying something more than classificatory about them.
After thousands of years of use, the concept remains central to biology and a host of related fields, and yet also remains at times ill-defined and controversial.
Implications of assignment of species status
The naming of a particular species should be regarded as a hypothesis about the evolutionary relationships and distinguishability of that group of organisms. As further information comes to hand, the hypothesis may be confirmed or refuted. Sometimes, especially in the past when communication was more difficult, taxonomists working in isolation have given two distinct names to individual organisms later identified as the same species. When two named species are discovered to be of the same species, the older species name is usually retained, and the newer species name dropped, a process called synonymization, or convivially, as lumping. Dividing a taxon into multiple, often new, taxons is called splitting. Taxonomists are often referred to as "lumpers" or "splitters" by their colleagues, depending on their personal approach to recognizing differences or commonalities between organisms (see lumpers and splitters).
Traditionally, researchers relied on observations of anatomical differences, and on observations of whether different populations were able to interbreed successfully, to distinguish species; both anatomy and breeding behavior are still important to assigning species status. As a result of the revolutionary (and still ongoing) advance in microbiological research techniques, including DNA analysis, in the last few decades, a great deal of additional knowledge about the differences and similarities between species has become available. Many populations which were formerly regarded as separate species are now considered to be a single taxon, and many formerly grouped populations have been split. Any taxonomic level (species, genus, family, etc.) can be synonymized or split, and at higher taxonomic levels, these revisions have been still more profound.
From a taxonomical point of view, groups within a species can be defined as being of a taxon hierarchically lower than a species. In zoology only the subspecies is used, while in botany the variety, subvariety, and form are used as well.
The isolation species concept in more detail
In general, for large, complex, organisms that reproduce sexually (such as mammals and birds), one of several variations on the isolation or biological species concept is employed. Often, the distinction between different species, even quite closely related ones, is simple. Horses (Equus caballus) and donkeys (Equus asinus) are easily told apart even without study or training, and yet are so closely related that they can interbreed after a fashion. Because the result, a mule or hinny, is not usually fertile, they are clearly separate species.
But many cases are more difficult to decide. This is where the isolation species concept diverges from the evolutionary species concept. Both agree that a species is a lineage that maintains its integrity over time, that is diagnosably different to other lineages (else we could not recognise it), is reproductively isolated (else the lineage would merge into others, given the chance to do so), and has a working intra-species recognition system (without which it could not continue). In practice, both also agree that a species must have its own independent evolutionary history—otherwise the characteristics just mentioned would not apply. The species concepts differ in that the evolutionary species concept does not make predictions about the future of the population: it simply records that which is already known. In contrast, the isolation species concept refuses to assign the rank of species to populations that, in the best judgement of the researcher, would recombine with other populations if given the chance to do so.
The isolation question
There are, essentially, two questions to resolve. First, is the proposed species consistently and reliably distinguishable from other species? Secondly, is it likely to remain so in the future? To take the second question first, there are several broad geographic possibilities.
- The proposed species are sympatric—they occupy the same habitat. Observation of many species over the years has failed to establish even a single instance of two diagnostically different populations that exist in sympatry and have then merged to form one united population. Without reproductive isolation, population differences cannot develop, and given reproductive isolation, gene flow between the populations cannot merge the differences. This is not to say that cross breeding does not take place at all, simply that it has become negligible. Generally, the hybrid individuals are less capable of successful breeding than pure-bred individuals of either species.
- The proposed species are allopatric—they occupy different geographical areas. Obviously, it is not possible to observe reproductive isolation in allopatric groups directly. Often it is not possible to achieve certainty by experimental means either: even if the two proposed species interbreed in captivity, this does not demonstrate that they would freely interbreed in the wild, nor does it always provide much information about the evolutionary fitness of hybrid individuals. A certain amount can be inferred from other experimental methods: for example, do the members of population A respond appropriately to playback of the recorded mating calls of population B? Sometimes, experiments can provide firm answers. For example, there are seven pairs of apparently almost identical marine snapping shrimp (Altheus) populations on either side of the Isthmus of Panama, which did not exist until about 3 million years ago. Until then, it is assumed, they were members of the same seven species. But when males and females from opposite sides of the isthmus are placed together, they fight instead of mating. Even if the isthmus were to sink under the waves again, the populations would remain genetically isolated: therefore they are now different species. In many cases, however, neither observation nor experiment can produce certain answers, and the determination of species rank must be made on a 'best guess' basis from a general knowledge of other related organisms.
- The proposed species are parapatric—they have breeding ranges that abut but do not overlap. This is fairly rare, particularly in temperate regions. The dividing line is often a sudden change in habitat (an ecotone) like the edge of a forest or the snow line on a mountain, but can sometimes be remarkably trivial. The parapatry itself indicates that the two populations occupy such similar ecological roles that they cannot coexist in the same area. Because they do not crossbreed, it is safe to assume that there is a mechanism, often behavioral, that is preventing gene flow between the populations, and that therefore they should be classified as separate species.
- There is a hybrid zone where the two populations mix. Typically, the hybrid zone will include representatives of one or both of the 'pure' populations, plus first-generation and back-crossing hybrids. The strength of the barrier to genetic transmission between the two pure groups can be assessed by the width of the hybrid zone relative to the typical dispersal distance of the organisms in question. The dispersal distance of oaks, for example, is the distance that a bird or squirrel can be expected to carry an acorn; the dispersal distance of Numbats is about 15 kilometres, as this is as far as young Numbats will normally travel in search of vacant territory to occupy after leaving the nest. The narrower the hybrid zone relative to the dispersal distance, the less gene flow there is between the population groups, and the more likely it is that they will continue on separate evolutionary paths. Nevertheless, it can be very difficult to predict the future course of a hybrid zone; the decision to define the two hybridizing populations as either the same species or as separate species is difficult and potentially controversial.
- The variation in the population is clinal; at either extreme of the population's geographic distribution, typical individuals are clearly different, but the transition between them is seamless and gradual. For example, the Koalas of northern Australia are clearly smaller and lighter in colour than those of the south, but there is no particular dividing line: the further south an individual Koala is found, the larger and darker it is likely to be; Koalas in intermediate regions are intermediate in weight and colour. In contrast, over the same geographic range, black-backed (northern) and white-backed (southern) Australian Magpies do not blend from one type to another: northern populations have black backs, southern populations white backs, and there is an extensive hybrid zone where both 'pure' types are common, as are crossbreeds. The variation in Koalas is clinal (a smooth transition from north to south, with populations in any given small area having a uniform appearance), but the variation in magpies is not clinal. In both cases, there is some uncertainty regarding correct classification, but the consensus view is that species rank is not justified in either. The gene flow between northern and southern magpie populations is judged to be sufficiently restricted to justify terming them subspecies (not full species); but the seamless way that local Koala populations blend one into another shows that there is substantial gene flow between north and south. As a result, experts tend to reject even subspecies rank in this case.
The difference question
Obviously, when defining a species, the geographic circumstances become meaningful only if the populations groups in question are clearly different: if they are not consistently and reliably distinguishable from one another, then we have no grounds for believing that they might be different species. The key question in this context, is "how different is different?" and the answer is usually "it all depends".
In theory, it would be possible to recognise even the tiniest of differences as sufficient to delineate a separate species, provided only that the difference is clear and consistent (and that other criteria are met). There is no universal rule to state the smallest allowable difference between two species, but in general, very trivial differences are ignored on the twin grounds of simple practicality, and genetic similarity: if two population groups are so close that the distinction between them rests on an obscure and microscopic difference in morphology, or a single base substitution in a DNA sequence, then a demonstration of restricted gene flow between the populations will probably be difficult in any case.
More typically, one or other of the following requirements must be met:
- It is possible to reliably measure a quantitative difference between the two groups that does not overlap. A population has, for example, thicker fur, rougher bark, longer ears, or larger seeds than another population, and although this characteristic may vary within each population, the two do not grade into one another, and given a reasonably large sample size, there is a definite discontinuity between them. Note that this applies to populations, not individual organisms, and that a small number of exceptional individuals within a population may 'break the rule' without invalidating it. The less a quantitative difference varies within a population and the more it varies between populations, the better the case for making a distinction. Nevertheless, borderline situations can only be resolved by making a 'best-guess' judgement.
- It is possible to distinguish a qualitative difference between the populations; a feature that does not vary continuously but is either entirely present or entirely absent. This might be a distinctively shaped seed pod, an extra primary feather, a particular courting behaviour, or a clearly different DNA sequence.
Sometimes it is not possible to isolate a single difference between species, and several factors must be taken in combination. This is often the case with plants in particular. In eucalypts, for example, Corymbia ficifolia cannot be reliably distinguished from its close relative Corymbia calophylla by any single measure (and sometimes individual trees cannot be definitely assigned to either species), but populations of Corymbia can be clearly told apart by comparing the colour of flowers, bark, and buds, number of flowers for a given size of tree, and the shape of the leaves and fruit.
When using a combination of characteristics to distinguish between populations, it is necessary to use a reasonably small number of factors (if more than a handful are needed, the genetic difference between the populations is likely to be insignificant and is unlikely to endure into the future), and to choose factors that are functionally independent (height and weight, for example, should usually be considered as one factor, not two).
Historical development of the species concept
In the earliest works of science, a species was simply an individual organism that represented a group of similar or nearly identical organisms. No other relationships beyond that group were implied. Aristotle used the words genus and species to mean generic and specific categories. Aristotle and other pre-Darwinian scientists took the species to be distinct and unchanging, with an "essence", like the chemical elements. When early observers began to develop systems of organization for living things, they began to place formerly isolated species into a context. To the modern mind, many of the schemes delineated are whimsical at best, such as those that determined consanguinity based on color (all plants with yellow flowers) or behavior (snakes, scorpions and certain biting ants).
In the 18th century Carolus Linnaeus classified organisms according to differences in the form of reproductive apparatus. Although his system of classification sorts organisms according to degrees of similarity, it made no claims about the relationship between similar species. At the time, it was still widely believed that there is no organic connection between species, no matter how similar they appear; every species was individually created by God, a view today called creationism. This approach also suggested a type of idealism: the notion that each species exists as an "ideal form". Although there are always differences (although sometimes minute) between individual organisms, Linnaeus considered such variation problematic. He strove to identify individual organisms that were exemplary of the species, and considered other non-exemplary organisms to be deviant and imperfect.
By the 19th century most naturalists understood that species could change form over time, and that the history of the planet provided enough time for major changes. As such, the new emphasis was on determining how a species could change over time. Jean-Baptiste Lamarck suggested that an organism could pass on an acquired trait to its offspring, i.e., the giraffe's long neck was attributed to generations of giraffes stretching to reach the leaves of higher treetops (this well-known and simplistic example, however, does not do justice to the breadth and subtlety of Lamarck's ideas).
Lamarck's most important insight may have been that species can be extraordinarily fluid; his 1809 Zoological Philosophy contained one of the first logical refutations of creationism. With the acceptance of the work of Charles Darwin in the 1860s, Lamarck's view of evolution was quickly eclipsed. It was not until the late 20th century that his work began to be reexamined, and took its place as a fundamental stepping stone to the modern theory of adaptive mutation. Lamarck's long-discarded ideas of the goal-oriented evolution of species, also known the teleological process, have also received renewed attention, particularly by proponents of artificial selection.
Charles Darwin and Alfred Wallace provided what scientists now consider the most powerful and compelling theory of evolution. Basically, Darwin argued that it is populations that evolve, not individuals. His argument relies on a radical shift in perspective from Linnaeus: rather than defining species in ideal terms (and searching for an ideal representative and rejecting deviations), Darwin considered variation among individuals to be natural. He further argued that variation, far from being problematic, actually provides the explanation for the existence of distinct species.
Darwin's work drew on Thomas Malthus' insight that the rate of growth of a biological population will always outpace the rate of growth of the resources in the environment, such as the food supply. As a result, Darwin argued, not all the members of a population will be able to survive and reproduce. Those that did will, on average, be the ones possessing variations—however slight—that make them slightly better adapted to the environment. If these variable traits are heritable, then the offspring of the survivors will also possess them. Thus, over many generations, adaptive variations will accumulate in the population, while counter-adaptive will be eliminated.
It should be emphasized that whether a variation is adaptive or non-adaptive depends on the environment: different environments favor different traits. Since the environment effectively selects which organisms live to reproduce, it is the environment (the "fight for existence") that selects the traits to be passed on. This is the theory of evolution by natural selection. In this model, the length of a giraffe's neck would be explained by positing that proto-giraffes with longer necks would have had a significant reproductive advantage to those with shorter necks. Over many generations, the entire population would be a species of long-necked animals.
In 1859, when Darwin published his theory of natural selection, the mechanism behind the inheritance of individual traits was unknown. Although Darwin made some speculations on how traits are inherited (pangenesis), his theory relies only on the fact that inheritable traits exist, and are variable (which makes his accomplishment even more remarkable.) Although Gregor Mendel's paper on genetics was published in 1866, its significance was not recognized. It was not until 1900 that his work was rediscovered by Hugo de Vries, Carl Correns and Erich von Tschermak, who realised that the "inheritable traits" in Darwin's theory are genes.
The theory of the evolution of species through natural selection has two important implications for discussions of species -- consequences that fundamentally challenge the assumptions behind Linnaeus' taxonomy. First, it suggests that species are not just similar, they may actually be related. Some students of Darwin argue that all species are descended from a common ancestor. Second, it supposes that "species" are not homogeneous, fixed, permanent things; members of a species are all different, and over time species change. This suggests that species do not have any clear boundaries but are rather momentary statistical effects of constantly changing gene-frequencies. One may still use Linnaeus' taxonomy to identify individual plants and animals, but one can no longer think of species as independent and immutable.
The rise of a new species from a parental line is called speciation. There is no clear line demarcating the ancestral species from the descendant species.
Although the current scientific understanding of species suggests there is no rigorous and comprehensive way to distinguish between different species in all cases, biologists continue to seek concrete ways to operationalize the idea. One of the most popular biological definitions of species is in terms of reproductive isolation; if two creatures cannot reproduce to produce fertile offspring, then they are in different species. This definition captures a number of intuitive species boundaries, but nonetheless has some problems, however. It has nothing to say about species that reproduce asexually, for example, and it is very difficult to apply to extinct species. Moreover, boundaries between species are often fuzzy: there are examples where members of one population can produce fertile offspring with a second population, and members of the second population can produce fertile offspring with members of a third population, but members of the first and third population cannot produces fertile offspring. Consequently, some people reject this notion of species.
In recent years we have witnessed the drastic reduction in the size of breeding populations and the geographical range of many physically large mammals. In earlier times it was assumed that every species existed in at least a few thousand living individuals, except very rare relic, isolated groups. In the present, many well know mammal & bird species are so stressed by habitat loss, and other effects of the modern world, that only a very few breeding males may contribute the genetic material to a small number of breeding females. In these highly stressed conditions, the likelihood of change is very much greater. Mammals may become smaller, have darker fur, more stripes, more cautious behavior, even over time learn to co-exist with the human world. Very likely, evolution is radically accelerated, and we are only beginning to notice it. Species in transition before our eyes. It is possible that this severe stress is essential to the creation of new species, and may have been a prime factor throughout biological history, from other population reducing influences.
Richard Dawkins defines two organisms as conspecific if and only if they have the same number of chromosomes and, for each chromosome, both organisms have the same number of nucleotides (The Blind Watchmaker, p. 118). However, most if not all taxonomists would strongly disagree. For example, in many amphibians, most notably in New Zealand's Leiopelma frogs, the genome consists of "core" chromosomes which are mostly invariable and accessory chromosomes, of which exist a number of possible combinations. Even though the chromosome numbers are highly variable between populations, these can interbreed successfully and form a single evolutionary unit. In plants, polyploidy is extremely commonplace with few restrictions on interbreeding; as individuals with an odd number of chromosome sets are usually sterile, depending on the actual number of chromosome sets present, this results in the odd situation where some individuals of the same evolutionary unit can interbreed with certain others and some cannot, with all populations being eventually linked as to form a common gene pool.
The classification of species has been profoundly affected by technological advances that have allowed researchers to determine relatedness based on molecular markers, starting with the comparatively crude blood plasma precipitation assays in the mid-20th century and coming into full swing with Charles Sibley's ground-breaking DNA-DNA hybridisation studies in the 1970s. The results of the technique caused revolutionary changes in the higher taxonomic categories (such as phyla and classes), resulting in the reordering of many branches of the phylogenetic tree (see also: molecular phylogeny). For taxonomic categories below genera, the results have been mixed so far; the pace of evolutionary change on the molecular level is rather slow, yielding clear differences only after considerable periods of reproductive separation. Instances of hybridization can result in misleading molecular data, the Pomarine Skua - Great Skua phenomenon being a famous example. Turtles have been determined to evolve with just one-eighth of the speed of other reptiles on the molecular level, and the rate of molecular evolution in albatrosses is half of what is found in the rather closely related storm-petrels. The hybridization technique is however no longer considered a good technique and more reliable computational techniques for sequence comparison are now used for. Molecular taxonomy does not directly measure the evolutionary processes, but rather the overall change brought upon by these processes. The processes that lead to the generation and maintenance of variation such as mutation, crossover and selection are not uniform (see also molecular clock). DNA is only extremely rarely a direct target of natural selection rather than changes in the DNA sequence enduring over generations being a result of the latter; for example, silent transition-transversion combinations would alter the melting point of the DNA sequence, but not the sequence of the encoded proteins and thus are a possible example where, for example in microorganisms, a mutation confers a change in fitness all by itself.
See also
- Speciation
- Cryptic species complex
- Ring species
External links
- http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/S/Speciation.html
- [http://www.sciencedaily.com/releases/2003/12/031231082553.htm 2003-12-31, ScienceDaily: Working On The 'Porsche Of Its Time': New Model For Species Determination Offered] Quote: "...two species of dinosaur that are members of the same genera varied from each other by just 2.2 percent. Translation of the percentage into an actual number results in an average of just three skeletal differences out of the total 338 bones in the body. Amazingly, 58 percent of these differences occurred in the skull alone. "This is a lot less variation than I'd expected", said Novak..."
- [http://www.sciencedaily.com/releases/2003/08/030808081854.htm 2003-08-08, ScienceDaily: Cross-species Mating May Be Evolutionarily Important And Lead To Rapid Change, Say Indiana University Researchers] Quote: "...the sudden mixing of closely related species may occasionally provide the energy to impel rapid evolutionary change..."
- [http://www.sciencedaily.com/releases/2004/01/040109064407.htm 2004-01-09 ScienceDaily: Mayo Researchers Observe Genetic Fusion Of Human, Animal Cells; May Help Explain Origin Of AIDS] Quote: "...The researchers have discovered conditions in which pig cells and human cells can fuse together in the body to yield hybrid cells that contain genetic material from both species... "What we found was completely unexpected", says Jeffrey Platt, M.D."
- [http://www.sciencedaily.com/releases/2000/09/000913211733.htm 2000-09-18, ScienceDaily: Scientists Unravel Ancient Evolutionary History Of Photosynthesis] Quote: "...gene-swapping was common among ancient bacteria early in evolution..."
- [http://plato.stanford.edu/entries/species/ Stanford Encyclopedia of Philosophy entry]
- [http://www.barcodinglife.org/ Barcoding of species]
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Category:Campephagidae
Campephagidae is a family of the Passeriformes order.
Category:Passeri TorkanTorkan is a heroic fantasy comic strip written and illustrated by Roger Fletcher. It first appeared in the Sunday Telegraph in 1976.
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