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128-659: Khammouane province covers an area of 16,315 square kilometres (6,299 sq mi) and is mostly of forested mountainous terrain. Many streams flow through the province to join the Mekong River . The vast forests of the Nakai-Nam Theun National Park are an important watershed that feed many Mekong tributaries as well as form the catchment area for Nam Theun 2 , the largest hydropower project in Laos. The Xe Bang Fai River , Nam Hinboun River , and

256-555: A drainage area of 795,000 km (307,000 sq mi), discharging 475 km (114 cu mi) of water annually. From its headwaters in the Tibetan Plateau , the river runs through Southwest China (where it is officially called the Lancang River ), Myanmar , Laos , Thailand , Cambodia , and southern Vietnam . The extreme seasonal variations in flow and the presence of rapids and waterfalls in

384-423: A mutation–selection balance . It is predicted that a viral quasispecies at a low but evolutionarily neutral and highly connected (that is, flat) region in the fitness landscape will outcompete a quasispecies located at a higher but narrower fitness peak in which the surrounding mutants are unfit, "the quasispecies effect" or the "survival of the flattest". There is no suggestion that a viral quasispecies resembles

512-477: A rodent in Khammouan representing a mammal family that had been previously known only from fossils . The Laotian rock rat or kha-nyou ( Laonastes aenigmamus ), also called the "rat-squirrel", was formally described as a new species in 2005. The species was first described in a 2005 article by Paulina Jenkins and coauthors, who considered the animal to be distinct from all living rodents. They placed it in

640-542: A two-part name , called a "binomial". The first part of a binomial is the genus to which the species belongs. The second part is called the specific name or the specific epithet (in botanical nomenclature , also sometimes in zoological nomenclature ). For example, Boa constrictor is one of the species of the genus Boa , with constrictor being the species' epithet. While the definitions given above may seem adequate at first glance, when looked at more closely they represent problematic species concepts. For example,

768-400: A "classical" method of determining species, such as with Linnaeus, early in evolutionary theory. However, different phenotypes are not necessarily different species (e.g. a four-winged Drosophila born to a two-winged mother is not a different species). Species named in this manner are called morphospecies . In the 1970s, Robert R. Sokal , Theodore J. Crovello and Peter Sneath proposed

896-424: A 'smallest clade' idea" (a phylogenetic species concept). Mishler and Wilkins and others concur with this approach, even though this would raise difficulties in biological nomenclature. Wilkins cited the ichthyologist Charles Tate Regan 's early 20th century remark that "a species is whatever a suitably qualified biologist chooses to call a species". Wilkins noted that the philosopher Philip Kitcher called this

1024-428: A connected series of neighbouring populations, each of which can sexually interbreed with adjacent related populations, but for which there exist at least two "end" populations in the series, which are too distantly related to interbreed, though there is a potential gene flow between each "linked" population. Such non-breeding, though genetically connected, "end" populations may co-exist in the same region thus closing

1152-789: A connection to the South China Sea. Although the hydraulic relationships between the Mekong and the Tonle Sap Great Lake systems during the Holocene are not well understood, it is clear that between 9,000 and 7,500 years ago the confluence of the Tonle Sap and the Mekong was in proximity to the South China Sea. The present river morphology of the Mekong Delta developed over the last 6,000 years. During this period,

1280-432: A different species from its ancestors. Viruses have enormous populations, are doubtfully living since they consist of little more than a string of DNA or RNA in a protein coat, and mutate rapidly. All of these factors make conventional species concepts largely inapplicable. A viral quasispecies is a group of genotypes related by similar mutations, competing within a highly mutagenic environment, and hence governed by

1408-604: A generic word for major rivers. To the early European traders, the Mekong River was also known as Mekon River , May-Kiang River and Cambodia River . The local names for the river include: The Mekong rises as the Za Qu ( Tibetan : རྫ་ཆུ་ , Wylie : rDza chu , ZYPY : Za qu ; Chinese : 扎曲 ; pinyin : Zā Qū ) and soon becomes known as the Lancang River ( simplified Chinese : 澜沧江 ; traditional Chinese : 瀾滄 江 ; pinyin : Láncāng Jiāng , from

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1536-508: A genetic boundary suitable for defining a species concept is present. DNA barcoding has been proposed as a way to distinguish species suitable even for non-specialists to use. One of the barcodes is a region of mitochondrial DNA within the gene for cytochrome c oxidase . A database, Barcode of Life Data System , contains DNA barcode sequences from over 190,000 species. However, scientists such as Rob DeSalle have expressed concern that classical taxonomy and DNA barcoding, which they consider

1664-478: A high evaporation rate means it is classified as a semi-arid region. Consequently, although the Mun and Chi basins drain 15% of the entire Mekong basin, they only contribute 6% of the average annual flow. Sandy and saline soils are the most common soil types, which makes much of the land unsuitable for wet rice cultivation. In spite of poor fertility, however, agriculture is intensive. Glutinous rice, maize, and cassava are

1792-465: A lineage should be divided into multiple chronospecies , or when populations have diverged to have enough distinct character states to be described as cladistic species. Species and higher taxa were seen from the time of Aristotle until the 18th century as categories that could be arranged in a hierarchy, the great chain of being . In the 19th century, biologists grasped that species could evolve given sufficient time. Charles Darwin 's 1859 book On

1920-468: A major distinction in the low-flow hydrology of the river. One fraction comes from melting snow in China and Tibet and the rest from over-season catchment storage in the lower basin. This has implications for the occurrence of drought conditions. For example, if runoff from melting snow in any given year is very low, then flows upstream of Vientiane - Nong Khai would be lower. In a large river system like

2048-591: A maximum of about 4.5 m (15 ft) above present levels in the early Holocene about 8 ka. At this time the shoreline of the South China Sea almost reached Phnom Penh and cores recovered from near Angkor Borei contained sediments deposited under the influence of tides, and salt marsh and mangrove swamp deposits. Sediments deposited in the Tonle Sap Great Lake about this time (7.9–7.3 ka) also show indications of marine influence, suggesting

2176-492: A misnomer, need to be reconciled, as they delimit species differently. Genetic introgression mediated by endosymbionts and other vectors can further make barcodes ineffective in the identification of species. A phylogenetic or cladistic species is "the smallest aggregation of populations (sexual) or lineages (asexual) diagnosable by a unique combination of character states in comparable individuals (semaphoronts)". The empirical basis – observed character states – provides

2304-622: A new family , Laonastidae . It is in the monotypic genus Laonastes .' Species of mammals, some discovered relatively recently, include the following (Robichaud 2005): saola , giant muntjac , Roosevelt's muntjac , Truong Son muntjac , Indochinese warty pig , Heude's pig , Annamite striped rabbit , Javan rhinoceros ( Rhinoceros sondaicus annamiticus ), Indochinese tiger , and Asian elephant . The 68,125 hectare Hin Nam No (also Hin Namno) Important Bird Area (IBA)

2432-449: A particular species, including which genus (and higher taxa) it is placed in, is a hypothesis about the evolutionary relationships and distinguishability of that group of organisms. As further information comes to hand, the hypothesis may be corroborated or refuted. Sometimes, especially in the past when communication was more difficult, taxonomists working in isolation have given two distinct names to individual organisms later identified as

2560-400: A perfect model of life, it is still a useful tool to scientists and conservationists for studying life on Earth, regardless of the theoretical difficulties. If species were fixed and clearly distinct from one another, there would be no problem, but evolutionary processes cause species to change. This obliges taxonomists to decide, for example, when enough change has occurred to declare that

2688-400: A short way of saying that something applies to many species within a genus, but not to all. If scientists mean that something applies to all species within a genus, they use the genus name without the specific name or epithet. The names of genera and species are usually printed in italics . However, abbreviations such as "sp." should not be italicised. When a species' identity is not clear,

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2816-404: A specialist may use "cf." before the epithet to indicate that confirmation is required. The abbreviations "nr." (near) or "aff." (affine) may be used when the identity is unclear but when the species appears to be similar to the species mentioned after. With the rise of online databases, codes have been devised to provide identifiers for species that are already defined, including: The naming of

2944-523: A species as groups of actually or potentially interbreeding natural populations, which are reproductively isolated from other such groups. It has been argued that this definition is a natural consequence of the effect of sexual reproduction on the dynamics of natural selection. Mayr's use of the adjective "potentially" has been a point of debate; some interpretations exclude unusual or artificial matings that occur only in captivity, or that involve animals capable of mating but that do not normally do so in

3072-400: A species as determined by a taxonomist. A typological species is a group of organisms in which individuals conform to certain fixed properties (a type), so that even pre-literate people often recognise the same taxon as do modern taxonomists. The clusters of variations or phenotypes within specimens (such as longer or shorter tails) would differentiate the species. This method was used as

3200-491: A species. All species definitions assume that an organism acquires its genes from one or two parents very like the "daughter" organism, but that is not what happens in HGT. There is strong evidence of HGT between very dissimilar groups of prokaryotes , and at least occasionally between dissimilar groups of eukaryotes , including some crustaceans and echinoderms . The evolutionary biologist James Mallet concludes that there

3328-685: A species. Generally the term includes the unknown element of a distinct act of creation. Many authors have argued that a simple textbook definition, following Mayr's concept, works well for most multi-celled organisms , but breaks down in several situations: Species identification is made difficult by discordance between molecular and morphological investigations; these can be categorised as two types: (i) one morphology, multiple lineages (e.g. morphological convergence , cryptic species ) and (ii) one lineage, multiple morphologies (e.g. phenotypic plasticity , multiple life-cycle stages). In addition, horizontal gene transfer (HGT) makes it difficult to define

3456-589: A stretch of some 2,200 km (1,400 mi). Here, it drops 4,500 m (14,800 ft) before it enters the lower basin where the borders of Thailand, Laos, China, and Myanmar come together in the Golden Triangle. Downstream from the Golden Triangle, the river flows for a further 2,600 km (1,600 mi) through Laos, Thailand, and Cambodia before entering the South China Sea via a complex delta system in Vietnam . The upper basin makes up 24% of

3584-528: A taxonomic decision at the discretion of cognizant specialists, is not governed by the Codes of Zoological or Botanical Nomenclature, in contrast to the PhyloCode , and contrary to what is done in several other fields, in which the definitions of technical terms, like geochronological units and geopolitical entities, are explicitly delimited. The nomenclatural codes that guide the naming of species, including

3712-517: A traditional biological species. The International Committee on Taxonomy of Viruses has since 1962 developed a universal taxonomic scheme for viruses; this has stabilised viral taxonomy. Most modern textbooks make use of Ernst Mayr 's 1942 definition, known as the Biological Species Concept as a basis for further discussion on the definition of species. It is also called a reproductive or isolation concept. This defines

3840-469: A unit of biodiversity . Other ways of defining species include their karyotype , DNA sequence, morphology , behaviour, or ecological niche . In addition, paleontologists use the concept of the chronospecies since fossil reproduction cannot be examined. The most recent rigorous estimate for the total number of species of eukaryotes is between 8 and 8.7 million. About 14% of these had been described by 2011. All species (except viruses ) are given

3968-447: A variation on the morphological species concept, a phenetic species, defined as a set of organisms with a similar phenotype to each other, but a different phenotype from other sets of organisms. It differs from the morphological species concept in including a numerical measure of distance or similarity to cluster entities based on multivariate comparisons of a reasonably large number of phenotypic traits. A mate-recognition species

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4096-515: A variety of reasons. Viruses are a special case, driven by a balance of mutation and selection , and can be treated as quasispecies . Biologists and taxonomists have made many attempts to define species, beginning from morphology and moving towards genetics . Early taxonomists such as Linnaeus had no option but to describe what they saw: this was later formalised as the typological or morphological species concept. Ernst Mayr emphasised reproductive isolation, but this, like other species concepts,

4224-438: Is "an entity composed of organisms which maintains its identity from other such entities through time and over space, and which has its own independent evolutionary fate and historical tendencies". This differs from the biological species concept in embodying persistence over time. Wiley and Mayden stated that they see the evolutionary species concept as "identical" to Willi Hennig 's species-as-lineages concept, and asserted that

4352-400: Is a group of sexually reproducing organisms that recognise one another as potential mates. Expanding on this to allow for post-mating isolation, a cohesion species is the most inclusive population of individuals having the potential for phenotypic cohesion through intrinsic cohesion mechanisms; no matter whether populations can hybridise successfully, they are still distinct cohesion species if

4480-458: Is a set of organisms adapted to a particular set of resources, called a niche, in the environment. According to this concept, populations form the discrete phenetic clusters that we recognise as species because the ecological and evolutionary processes controlling how resources are divided up tend to produce those clusters. A genetic species as defined by Robert Baker and Robert Bradley is a set of genetically isolated interbreeding populations. This

4608-465: Is bordered by Bolikhamsai province to the north and northwest, Vietnam to the east, Savannakhet province to the south, and Thailand to the west. Many streams flow through the province to join the Mekong River. The major rivers originating in the mountains of the province are the Xebangfay River (239 kilometres (149 mi) long), Nam Hinboun , Nam Theun , and Nam Ngum River . Between

4736-414: Is called speciation . Charles Darwin was the first to describe the role of natural selection in speciation in his 1859 book The Origin of Species . Speciation depends on a measure of reproductive isolation , a reduced gene flow. This occurs most easily in allopatric speciation, where populations are separated geographically and can diverge gradually as mutations accumulate. Reproductive isolation

4864-403: Is described formally, in a publication that assigns it a unique scientific name. The description typically provides means for identifying the new species, which may not be based solely on morphology (see cryptic species ), differentiating it from other previously described and related or confusable species and provides a validly published name (in botany) or an available name (in zoology) when

4992-477: Is flooded during the rainy season. The impact of road embankments and similar infrastructure developments on the movement of this flood water is an increasingly important consequence of development. Table 2 summarises the mean annual flows along the mainstream. The mean annual flow entering the lower Mekong from China is equivalent to a relatively modest 450 mm (18 in) depth of runoff. Downstream of Vientiane this increases to over 600 mm (24 in) as

5120-671: Is further weakened by the existence of microspecies , groups of organisms, including many plants, with very little genetic variability, usually forming species aggregates . For example, the dandelion Taraxacum officinale and the blackberry Rubus fruticosus are aggregates with many microspecies—perhaps 400 in the case of the blackberry and over 200 in the dandelion, complicated by hybridisation , apomixis and polyploidy , making gene flow between populations difficult to determine, and their taxonomy debatable. Species complexes occur in insects such as Heliconius butterflies, vertebrates such as Hypsiboas treefrogs, and fungi such as

5248-726: Is hard or even impossible to test. Later biologists have tried to refine Mayr's definition with the recognition and cohesion concepts, among others. Many of the concepts are quite similar or overlap, so they are not easy to count: the biologist R. L. Mayden recorded about 24 concepts, and the philosopher of science John Wilkins counted 26. Wilkins further grouped the species concepts into seven basic kinds of concepts: (1) agamospecies for asexual organisms (2) biospecies for reproductively isolated sexual organisms (3) ecospecies based on ecological niches (4) evolutionary species based on lineage (5) genetic species based on gene pool (6) morphospecies based on form or phenotype and (7) taxonomic species,

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5376-528: Is heterogeneous and active, and is the major factor controlling the course of rivers and the landscapes they carve out. The elevation of the Tibetan Plateau during the Tertiary period was an important factor in the genesis of the south-west monsoon , which is the dominant climatic control influencing the hydrology of the Mekong Basin. Understanding the nature and timing of the elevation of Tibet (and

5504-618: Is in the Hin Namno NBCA. Its topography features limestone karst outcrops, undulating limestone hills, as well as valleys. The IBA's habitat is characterized by sparsely vegetated limestone karst, semi-evergreen tropical rain forest, mixed deciduous forest, moist deciduous tropical forest, and wet evergreen forest. Vietnamese crested argus ( Rheinardia ocellata ) and Austen's brown hornbill ( Anorrhinus austeni ) are classified as near threatened. The inornate squirrel ( Callosciurus inornatus ) has been identified as important fauna within

5632-429: Is in the range of 20 metres (66 ft) to 100 metres (330 ft). The Hinboun River flows through the cave perennially. Vang That and Had Xay Luang are the two hanging rock formations in the cave. Had Xay Luang is a white sand beach here, of about 150 metres (490 ft) in length and 100 metres (330 ft) width. The cave is approachable along two routes, one from Vientiane along Route 13 to Hinboun District, and

5760-531: Is little evidence from the last 45 years of data of any systematic changes in the hydrological regime of the Mekong. The internal drainage patterns of the Mekong are unusual among those of large rivers. Most large river systems that drain the interiors of continents, such as the Amazon , Congo , and Mississippi , have relatively simple dendritic tributary networks that resemble a branching tree. Typically, such patterns develop in basins with gentle slopes where

5888-403: Is no easy way to tell whether related geographic or temporal forms belong to the same or different species. Species gaps can be verified only locally and at a point of time. One is forced to admit that Darwin's insight is correct: any local reality or integrity of species is greatly reduced over large geographic ranges and time periods. The botanist Brent Mishler argued that the species concept

6016-478: Is not valid, notably because gene flux decreases gradually rather than in discrete steps, which hampers objective delimitation of species. Indeed, complex and unstable patterns of gene flux have been observed in cichlid teleosts of the East African Great Lakes . Wilkins argued that "if we were being true to evolution and the consequent phylogenetic approach to taxa, we should replace it with

6144-586: Is similar to Mayr's Biological Species Concept, but stresses genetic rather than reproductive isolation. In the 21st century, a genetic species could be established by comparing DNA sequences. Earlier, other methods were available, such as comparing karyotypes (sets of chromosomes ) and allozymes ( enzyme variants). An evolutionarily significant unit (ESU) or "wildlife species" is a population of organisms considered distinct for purposes of conservation. In palaeontology , with only comparative anatomy (morphology) and histology from fossils as evidence,

6272-675: Is the beginning of the Mekong Delta. The two rivers, the Bassac to the west and the Mekong to the east, enter Vietnam shortly after this. In Vietnam, the Bassac is called the Hậu River (Sông Hậu or Hậu Giang); the main, eastern, branch of the Mekong is called the Tiền River or Tiền Giang. In Vietnam, distributaries of the eastern (main, Mekong) branch include the Mỹ Tho River , the Ba Lai River ,

6400-594: Is threatened by hybridisation, but this can be selected against once a pair of populations have incompatible alleles of the same gene, as described in the Bateson–Dobzhansky–Muller model . A different mechanism, phyletic speciation, involves one lineage gradually changing over time into a new and distinct form (a chronospecies ), without increasing the number of resultant species. Horizontal gene transfer between organisms of different species, either through hybridisation , antigenic shift , or reassortment ,

6528-475: Is used for large rivers and Khong is the proper name referred to as "River Khong". However, Khong is an archaic word meaning "river", loaned from Austroasiatic languages , such as Vietnamese sông (from * krong ) and Mon kruŋ "river", which led to Chinese 江 whose Old Chinese pronunciation has been reconstructed as /*kˤroŋ/ and which long served as the proper name of the Yangtze before becoming

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6656-570: The Central Highlands of Vietnam) therefore helps explain the provenance of sediment reaching the delta and the Tonle Sap Great Lake today. Studies of the provenance of sediments in the Mekong delta reveal a major switch in the source of sediments about eight million years ago (Ma) . From 36 to 8 Ma the bulk (76%) of the sediments deposited in the delta came from erosion of the bedrock in the Three Rivers Area . From 8 Ma to

6784-591: The Hàm Luông River , and the Cổ Chiên River . The Mekong Basin is frequently divided into two parts: the "upper Mekong basin" comprising those parts of the basin in Tibet , Yunnan and eastern Myanmar , and the "lower Mekong basin" from Yunnan downstream from China to the South China Sea . From the point where it rises to its mouth, the most precipitous drop in the Mekong occurs in the upper Mekong basin,

6912-530: The ICZN for animals and the ICN for plants, do not make rules for defining the boundaries of the species. Research can change the boundaries, also known as circumscription, based on new evidence. Species may then need to be distinguished by the boundary definitions used, and in such cases the names may be qualified with sensu stricto ("in the narrow sense") to denote usage in the exact meaning given by an author such as

7040-591: The Nam Ngum , Nam Theun , Nam Hinboun, Se Bang Fai , Se Bang Hieng and Se Done Rivers. The Mun - Chi river system from the right bank in Thailand enters the mainstream within this reach. Reach 4: Pakse to Kratie . The main hydrological contributions to the mainstream in this reach come from the Se Kong , Se San , and Sre Pok catchments. Together, these rivers make up the largest hydrological sub-component of

7168-532: The Nam Theun are the main rivers of the province. Part of the aborted Thakhek-Tan Ap railway would have crossed the province to connect with the North-South Railway at Tân Ấp Railway Station , Quảng Bình province , Vietnam through Mụ Giạ Pass . Khammouane province covers an area of 16,315 square kilometres (6,299 sq mi) and is mostly of forested mountainous terrain. The province

7296-465: The Richter magnitude scale and is unlikely to cause material damage. The difficulty of navigating the river has meant that it has divided, rather than united, the people who live near it. The earliest known settlements date to 210 BCE, with Ban Chiang being an excellent example of early Iron Age culture. The earliest recorded civilization was the 1st century Indianised -Khmer culture of Funan , in

7424-826: The Three Parallel Rivers Area in the Hengduan Mountains , along with the Yangtze to its east and the Salween River (Nu Jiang in Chinese) to its west. Then the Mekong meets the China–Myanmar border and flows about 10 km (6 mi) along that border until it reaches the tripoint of China, Myanmar and Laos . From there it flows southwest and forms the border of Myanmar and Laos for about 100 km (60 mi) until it arrives at

7552-587: The Tonlé Sap . When the Mekong is low, the Tonle Sap is a tributary : water flows from the lake and river into the Mekong. When the Mekong floods, the flow reverses: the floodwaters of the Mekong flow up the Tonle Sap. Immediately after the Sap River joins the Mekong by Phnom Penh, the Bassac River branches off the right (west) bank. The Bassac River is the first and main distributary of the Mekong. This

7680-633: The Yunnan component makes up almost 30% of the average dry season flow. A major concern is that the ongoing and planned expansion of dams and reservoirs on the Mekong mainstream in Yunnan could have a significant effect on the low-flow regime of the lower Mekong basin system. Reach 2: Chiang Saen to Vientiane and Nong Khai . This reach is almost entirely mountainous and covered with natural forest although there has been widespread slash and burn agriculture. Although this reach cannot be termed "unspoiled",

7808-399: The fly agaric . Natural hybridisation presents a challenge to the concept of a reproductively isolated species, as fertile hybrids permit gene flow between two populations. For example, the carrion crow Corvus corone and the hooded crow Corvus cornix appear and are classified as separate species, yet they can hybridise where their geographical ranges overlap. A ring species is

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7936-507: The jaguar ( Panthera onca ) of Latin America or the leopard ( Panthera pardus ) of Africa and Asia. In contrast, the scientific names of species are chosen to be unique and universal (except for some inter-code homonyms ); they are in two parts used together : the genus as in Puma , and the specific epithet as in concolor . A species is given a taxonomic name when a type specimen

8064-406: The "cynical species concept", and arguing that far from being cynical, it usefully leads to an empirical taxonomy for any given group, based on taxonomists' experience. Other biologists have gone further and argued that we should abandon species entirely, and refer to the "Least Inclusive Taxonomic Units" (LITUs), a view that would be coherent with current evolutionary theory. The species concept

8192-547: The 1950s to around 50% in the mid-1990s. Agricultural expansion and population pressure are the major reasons for land use and landscape change. Both drought and flood are common hazards in the Delta, which many people believe is the most sensitive to upstream hydrological change. Table 1: Country share of Mekong River Basin (MRB) and water flows By taking into account hydrological regimes, physiography land use, and existing, planned and potential resource developments,

8320-780: The Great Lake via the Tonle Sap River . Phnom Penh also marks the beginning of the delta system of the Mekong River. Here the mainstream begins to break up into an increasing number of branches. In Cambodia, wet rice is the main crop and is grown on the flood plains of the Tonle Sap, Mekong, and Bassac (the Mekong delta distributary known as the Hậu in Vietnam) Rivers. More than half of Cambodia remains covered with mixed evergreen and deciduous broadleaf forest, but forest cover has decreased from 73% in 1973 to 63% in 1993. Here,

8448-592: The IBA. The Khammouane IBA is in the Phou Hin Poun NBCA. The IBA is 79,000 ha in size with an elevation of 200–900 metres (660–2,950 ft). The topography and habitat are characterized by sparsely vegetated limestone karst, semi-evergreen forest, mixed deciduous forest, as well as non-calcareous substrate. The IBA is notable for supporting the sooty babbler ( Stachyris herberti ) and a taxon of François' langur ( Trachypithecus francoisi ). The population of

8576-734: The Kingdom of Thailand which is the mechanism for cooperation with regard to riverine trade on the upper stretches of the Mekong. The Mekong basin is one of the richest areas of biodiversity in the world. Only the Amazon boasts a higher level of bio-diversity. Biota estimates for the Greater Mekong Subregion (GMS) include 20,000 plant species, 430 mammals, 1,200 birds, 800 reptiles and amphibians, and an estimated 850 freshwater fish species (excluding euryhaline species mainly found in salt or brackish water, as well as introduced species ). The most species rich orders among

8704-478: The Laos-Thailand border for some 850 km (530 mi) as it flows first east, passing the capital of Laos, Vientiane , then turns south. A second time, the river leaves the border and flows east into Laos soon passing the city of Pakse . Thereafter, it turns and runs more or less directly south, crossing into Cambodia . At Phnom Penh the river is joined on the right bank by the river and lake system

8832-731: The Mekong River. The bridge is 1,423 metres (4,669 ft) long and 13 metres (43 ft) wide. Tham Khonglor Cave (meaning: 'beauty in the dark') is part of the National Protected Forest Area in Hinboun Mountain. Its west entrance is from Ban Khonglor village in Hinboun District , while the east entrance is from Ban Natan village, Nakai District . The cave runs for a length of about 7.4 kilometres (4.6 mi). Its width varies from 10 metres (33 ft) to 90 metres (300 ft). Its height

8960-599: The Mekong and the Annamite Range , the Khammouane Plateau features gorges, grottoes, jungles, limestone hills, and rivers. Thakhek , the provincial capital, is on the Mekong River bordering Thailand. The border checkpoint is Nakhon Phanom . The city has many buildings designed in the French colonial architectural style. The Third Thai–Lao Friendship Bridge , opened to traffic on 11 November 2011, spans

9088-630: The Mekong delta. Excavations at Oc Eo , near modern An Giang , have found coins from as far away as the Roman Empire . This was succeeded by the Khmer culture Chenla state around the 5th century. The Khmer empire of Angkor was the last great Indianized state in the region. From around the time of the fall of the Khmer empire, the Mekong was the front line between the emergent states of Siam and Tonkin (North Vietnam), with Laos and Cambodia, then on

9216-467: The Mekong is divided into six distinct reaches : Reach 1: Lancang Jiang or Upper Mekong River in China . In this part of the river, the major source of water flowing into the river comes from melting snow on the Tibetan plateau . This volume of water is sometimes called the "Yunnan component" and plays an important role in the low-flow hydrology of the lower mainstream. Even as far downstream as Kratie,

9344-465: The Mekong make navigation difficult. Even so, the river is a major trade route between Tibet and Southeast Asia. The construction of hydroelectric dams along the Mekong in the 2000s through the 2020s has caused serious problems for the river's ecosystem , including the exacerbation of drought . The Mekong was originally called Mae Nam Khong from a contracted form of Tai shortened to Mae Khong . In Thai and Lao, Mae Nam ("Mother of Water[s]")

9472-655: The Mekong, seasonal flows can be quite variable from year to year. Although the pattern of the annual hydrograph is fairly predictable, its magnitude is not. The average monthly flows along the mainstream are listed in Table 3, providing an indication of their range and variability from year to year. At Pakse , for example, flood season flows during August would exceed 20,000 m /s (5,300,000 US gal/s) nine years out of ten, but exceed 34,000 m /s (9,000,000 US gal/s) only one year in ten. Table 3: Mekong Mainstream monthly discharge, 1960–2004 (m /s). There

9600-442: The Mun and Chi Rivers, that drain a large part of northeast Thailand. Laos lies almost entirely within the lower Mekong basin. Its climate, landscape and land use are the major factors shaping the hydrology of the river. The mountainous landscape means that only 16% of the country is farmed under lowland terrace or upland shifting cultivation . With upland shifting agriculture (slash and burn), soils recover within 10 to 20 years but

9728-626: The Origin of Species explained how species could arise by natural selection . That understanding was greatly extended in the 20th century through genetics and population ecology . Genetic variability arises from mutations and recombination , while organisms themselves are mobile, leading to geographical isolation and genetic drift with varying selection pressures . Genes can sometimes be exchanged between species by horizontal gene transfer ; new species can arise rapidly through hybridisation and polyploidy ; and species may become extinct for

9856-405: The abbreviation "sp." in the singular or "spp." (standing for species pluralis , Latin for "multiple species") in the plural in place of the specific name or epithet (e.g. Canis sp.). This commonly occurs when authors are confident that some individuals belong to a particular genus but are not sure to which exact species they belong, as is common in paleontology . Authors may also use "spp." as

9984-570: The amount of hybridisation is insufficient to completely mix their respective gene pools . A further development of the recognition concept is provided by the biosemiotic concept of species. In microbiology , genes can move freely even between distantly related bacteria, possibly extending to the whole bacterial domain. As a rule of thumb, microbiologists have assumed that members of Bacteria or Archaea with 16S ribosomal RNA gene sequences more similar than 97% to each other need to be checked by DNA–DNA hybridisation to decide if they belong to

10112-474: The basin are small. Only 14 have catchment areas that exceed 1,000 km (400 sq mi), yet the greatest amount of loss of forest cover in the entire river system per square kilometer has occurred in this region due to heavy unchecked demand for natural resources. In the south of Yunnan, in Simao and Xishuangbanna Prefectures, the river changes as the valley opens out, the floodplain becomes wider, and

10240-474: The biological species concept, "the several versions" of the phylogenetic species concept, and the idea that species are of the same kind as higher taxa are not suitable for biodiversity studies (with the intention of estimating the number of species accurately). They further suggested that the concept works for both asexual and sexually-reproducing species. A version of the concept is Kevin de Queiroz 's "General Lineage Concept of Species". An ecological species

10368-505: The biological species concept, a cladistic species does not rely on reproductive isolation – its criteria are independent of processes that are integral in other concepts. Therefore, it applies to asexual lineages. However, it does not always provide clear cut and intuitively satisfying boundaries between taxa, and may require multiple sources of evidence, such as more than one polymorphic locus, to give plausible results. An evolutionary species, suggested by George Gaylord Simpson in 1951,

10496-428: The border of Laos with Thailand. Khon Pi Long is a series of rapids along a 1.6 km (1.0 mi) section of the Mekong River dividing Chiang Rai and Bokeo Province in Laos. The name of the rapids means 'where the ghost lost its way'. It then turns east into the interior of Laos, flowing first east and then south for some 400 km (250 mi) before meeting the border with Thailand again. Once more, it defines

10624-428: The boundaries between closely related species become unclear with hybridisation , in a species complex of hundreds of similar microspecies , and in a ring species . Also, among organisms that reproduce only asexually , the concept of a reproductive species breaks down, and each clone is potentially a microspecies. Although none of these are entirely satisfactory definitions, and while the concept of species may not be

10752-600: The coast, torn between their influence. The first European to encounter the Mekong was the Portuguese António de Faria in 1540. A European map of 1563 depicts the river, although even by then little was known of the river upstream of the delta. European interest was sporadic: the Spanish and Portuguese mounted some missionary and trade expeditions, while the Dutch Gerrit van Wuysthoff led an expedition up

10880-433: The concept of a chronospecies can be applied. During anagenesis (evolution, not necessarily involving branching), some palaeontologists seek to identify a sequence of species, each one derived from the phyletically extinct one before through continuous, slow and more or less uniform change. In such a time sequence, some palaeontologists assess how much change is required for a morphologically distinct form to be considered

11008-497: The delta advanced 200 km (120 mi) over the continental shelf of the South China Sea, covering an area of more than 62,500 km (24,100 sq mi). From 5.3 to 3.5 ka the delta advanced across a broad embayment formed between higher ground near the Cambodian border and uplands north of Ho Chi Minh City . During this phase of its development the delta was sheltered from the wave action of long-shore currents and

11136-452: The delta. For much of its length the Mekong flows through bedrock channels, i.e., channels that are confined or constrained by bedrock or old alluvium in the bed and riverbanks. Geomorphologic features normally associated with the alluvial stretches of mature rivers, such as meanders , oxbow lakes , cut-offs, and extensive floodplains are restricted to a short stretch of the mainstream around Vientiane and downstream of Kratie where

11264-832: The district, inundating almost 700 hectares, destroying dozens of fishponds and killing 112 cattle. There are several major operating mining companies in the province, including Mining Development Economy Corporation mining gypsum in Thakhek District, LAVICO Co. Ltd, which is a Laos-Vietnam joint venture mining gypsum in Xebangfay District, V.S.K. Co. Ltd mining limestone in Thakhek District), and Lao-North Korea Tin Mines mining tin in Hinboun District. Several culinary specialties are also native

11392-575: The east of Thakhek District), Wat Pha Sokkhamsene Temple (an old temple near Nongbok District and about 37 km from Thakhek District), and That Thumphavang Stupa (to the north of Nongbok District). Mekong River The Mekong or Mekong River is a trans-boundary river in East Asia and Southeast Asia . It is the world's twelfth-longest river and the third-longest in Asia with an estimated length of 4,909 km (3,050 mi) and

11520-435: The evidence to support hypotheses about evolutionarily divergent lineages that have maintained their hereditary integrity through time and space. Molecular markers may be used to determine diagnostic genetic differences in the nuclear or mitochondrial DNA of various species. For example, in a study done on fungi , studying the nucleotide characters using cladistic species produced the most accurate results in recognising

11648-423: The freshwater fish in the river basin are cypriniforms (377 species) and catfish (92 species). Species A species ( pl. : species) is a population of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring , typically by sexual reproduction . It is the basic unit of classification and a taxonomic rank of an organism, as well as

11776-750: The hydrological impacts of land cover changes induced by the Vietnam War were quantified in two sub-catchments of the lower Mekong River basin. Loss of forest cover in the Thai areas of the lower basin has been the highest of all the lower Mekong countries over the past 60 years. On the Khorat Plateau , which includes the Mun and Chi tributary systems, forest cover was reduced from 42% in 1961 to 13% in 1993. Although this part of northeast Thailand has an annual rainfall of more than 1,000 mm (40 in),

11904-437: The hydrological response is perhaps the most natural and undisturbed of all the lower basin. Many hydrological aspects of the lower basin start to change rapidly at the downstream boundary of this reach. On 19 July 2019 this reach of the river dropped to its lowest level in a century. Officials are particularly concerned as July is in the wet season, when mainstream flows are abundant historically. Locals are blaming low water on

12032-437: The lower basin from Yunnan make up about 15% of the wet season flow at Kratie . This rises to 40% during the dry season, even this far downstream. During the wet season, the proportion of average flow coming from Yunnan rapidly decreases downstream of Chiang Saen, from 70% to less than 20% at Kratie. The dry season contribution from Yunnan is much more significant. The major portion of the balance comes from Laos, which points to

12160-467: The lower basin. Over 25% of the mean annual flow volume to the mainstream at Kratie comes from these three river basins. They are the key element in the hydrology of this part of the system, especially to the Tonle Sap flow reversal. Reach 5: Kratie to Phnom Penh . This reach includes the hydraulic complexities of the Cambodian floodplain, the Tonle Sap and the Great Lake. By this stage, over 95% of

12288-560: The newly constructed Xayaburi Dam , as it enters its test phase prior to the start of commercial operation in October 2019. Reach 3: Vientiane and Nong Khai to Pakse . The boundary between Reach 2 and 3 is where the Mekong hydrology starts to change. Reach 2 is dominated in both wet and dry seasons by the Yunnan Component. Reach 3 is increasingly influenced by contributions from the large left bank tributaries in Laos, namely

12416-483: The numerous fungi species of all the concepts studied. Versions of the phylogenetic species concept that emphasise monophyly or diagnosability may lead to splitting of existing species, for example in Bovidae , by recognising old subspecies as species, despite the fact that there are no reproductive barriers, and populations may intergrade morphologically. Others have called this approach taxonomic inflation , diluting

12544-749: The old name of Lao kingdom Lan Xang ; the characters may also be literally understood as "turbulent green river"). It originates in the " three rivers source area " on the Tibetan Plateau in the Sanjiangyuan National Nature Reserve . The reserve protects the headwaters of, from north to south, the Yellow (Huang He), the Yangtze , and the Mekong Rivers. It flows through the Tibetan Autonomous Region and then southeast into Yunnan Province, and then

12672-593: The paper is accepted for publication. The type material is usually held in a permanent repository, often the research collection of a major museum or university, that allows independent verification and the means to compare specimens. Describers of new species are asked to choose names that, in the words of the International Code of Zoological Nomenclature , are "appropriate, compact, euphonious, memorable, and do not cause offence". Books and articles sometimes intentionally do not identify species fully, using

12800-674: The person who named the species, while the antonym sensu lato ("in the broad sense") denotes a wider usage, for instance including other subspecies. Other abbreviations such as "auct." ("author"), and qualifiers such as "non" ("not") may be used to further clarify the sense in which the specified authors delineated or described the species. Species are subject to change, whether by evolving into new species, exchanging genes with other species, merging with other species or by becoming extinct. The evolutionary process by which biological populations of sexually-reproducing organisms evolve to become distinct or reproductively isolated as species

12928-727: The present, however, the contribution from the Three Rivers Area fell to 40%, while that from the Central Highlands rose from 11 to 51%. One of the most striking conclusions of provenance studies is the small contribution of sediment from the other parts of the Mekong basin, notably the Khorat Plateau, the uplands of northern Laos and northern Thailand, and the mountain ranges south of the Three Rivers area. The last glacial period came to an abrupt end about 19,000 years ago (19 ka ) when sea levels rose rapidly, reaching

13056-436: The principal crops. Drought is by far the major hydrological hazard in this region. As the Mekong enters Cambodia, over 95% of its flows have already joined the river. From here on downstream the terrain is flat and water levels rather than flow volumes determine the movement of water across the landscape. The seasonal cycle of changing water levels at Phnom Penh results in the unique "flow reversal" of water into and out of

13184-796: The principal left bank tributaries enter the mainstream, mainly the Nam Ngum and Nam Theun. The flow level falls again, even with the right bank entry of the Mun-Chi system from Thailand. Although the Mun–Chi basin drains 20% of the lower system, average annual runoff is only 250 mm (10 in). Runoff in the mainstream increases again with the entry from the left bank of the Se Kong from southern Laos and Se San and Sre Pok from Vietnam and Cambodia. Table 2: Lower Mekong Mainstream annual flow (1960 to 2004) at selected sites. Flows at Chiang Saen entering

13312-491: The province according to the 2015 census is 392,052. The province is composed of the following nine districts: Thakhek , the provincial capital, is an important centre for trade. Along with Bolikhamsai and Savannakhet provinces, it is one of the main tobacco producing areas of Laos. Part of the province, particularly Yommalath District , was badly affected by floods caused by heavy rain in July 2011, affecting rice farmland in

13440-585: The province including Kha Nom Phane , a type of rice cake. That Sikhottabong , also known as Sikhottabong Stupa, is a contemporary of That Inhangin Savannakhet and That Phanom , built in Thailand under the Sikhottabong Empire . The bones of Buddha are said to be consecrated in these temples. King Nanthasene built the stupa for King Soummitham. It was refurbished in the 15th century during

13568-436: The reign by King Saysethathirath. The stupa has four squares with each side measuring 25,030 metres (82,120 ft) long and its base is 14.33 square metres (154.2 sq ft) and rises to a height of 29 metres (95 ft). The pinnacle appears in the shape of the banana flower. The stupa is seen on the bank of the Mekong River. Its festival is held during the third lunar month . The Great Wall, built of stones, starts on

13696-487: The result of misclassification leading to questions on whether there really are any ring species. The commonly used names for kinds of organisms are often ambiguous: "cat" could mean the domestic cat, Felis catus , or the cat family, Felidae . Another problem with common names is that they often vary from place to place, so that puma, cougar, catamount, panther, painter and mountain lion all mean Puma concolor in various parts of America, while "panther" may also mean

13824-535: The ring. Ring species thus present a difficulty for any species concept that relies on reproductive isolation. However, ring species are at best rare. Proposed examples include the herring gull – lesser black-backed gull complex around the North pole, the Ensatina eschscholtzii group of 19 populations of salamanders in America, and the greenish warbler in Asia, but many so-called ring species have turned out to be

13952-495: The river as far as Vientiane in 1641–42. The French invaded the region in the mid-19th century, capturing Saigon in 1861, and establishing a protectorate over Cambodia in 1863. The first systematic European exploration began with the French Mekong Expedition led by Ernest Doudard de Lagrée and Francis Garnier , which ascended the river from its mouth to Yunnan between 1866 and 1868. Their chief finding

14080-400: The river becomes wider and slower. Major tributary systems develop in the lower basin. These systems can be separated into two groups: tributaries that contribute to the major wet season flows, and tributaries that drain low relief regions of lower rainfall. The first group are left bank tributaries that drain the high rainfall areas of Laos. The second group are those on the right bank, mainly

14208-448: The river develops alluvial channels that are free of control exerted by the underlying bedrock. The Mekong basin is not normally considered a seismically active area as much of the basin is underlain by the relatively stable continental block. Nonetheless, the parts of the basin in northern Laos , northern Thailand , Myanmar and China do experience frequent earthquakes and tremors. The magnitude of these earthquakes rarely exceeds 6.5 on

14336-464: The river landscape is flat. Small changes in water level determine the direction of water movement, including the large-scale reversal of flow into and out of the Tonle Sap basin from the Mekong River. The Mekong Delta in Vietnam is farmed intensively and has little natural vegetation left. Forest cover is less than 10%. In the Central Highlands of Vietnam, forest cover was reduced from over 95% in

14464-508: The same species. This concept was narrowed in 2006 to a similarity of 98.7%. The average nucleotide identity (ANI) method quantifies genetic distance between entire genomes , using regions of about 10,000 base pairs . With enough data from genomes of one genus, algorithms can be used to categorize species, as for Pseudomonas avellanae in 2013, and for all sequenced bacteria and archaea since 2020. Observed ANI values among sequences appear to have an "ANI gap" at 85–95%, suggesting that

14592-529: The same species. When two species names are discovered to apply to the same species, the older species name is given priority and usually retained, and the newer name considered as a junior synonym, a process called synonymy . Dividing a taxon into multiple, often new, taxa is called splitting . Taxonomists are often referred to as "lumpers" or "splitters" by their colleagues, depending on their personal approach to recognising differences or commonalities between organisms. The circumscription of taxa, considered

14720-922: The second route is by boat along the Hinboun River. The province's forest areas consists of three reserve areas. These are the Nakai-Nam Theun National Park, which covers an area of 352,200 ha of the Annamite mountains and the adjacent Nakai Plateau in the provinces of Khammouane and Bolikhamxay, the Hin Namno National Park with an area of 86,229 ha, and the Phou Hin Poun National Biodiversity Conservation Area with an area of 150,000 ha. These forests have many natural caves. In 1996, Western scientists discovered

14848-506: The species concept and making taxonomy unstable. Yet others defend this approach, considering "taxonomic inflation" pejorative and labelling the opposing view as "taxonomic conservatism"; claiming it is politically expedient to split species and recognise smaller populations at the species level, because this means they can more easily be included as endangered in the IUCN red list and can attract conservation legislation and funding. Unlike

14976-633: The support of the Office of Weapons Removal and Abatement within the US State Department Bureau of Political-Military Affairs , to conduct underwater explosive removal. The many maps of the river basin produced throughout recorded history reflect the region's changing human geography and politics. In 1995, Laos, Thailand, Cambodia, and Vietnam established the Mekong River Commission (MRC) to manage and coordinate

15104-409: The total area and contributes 15–20% of the water that flows into the Mekong River. The catchment here is steep and narrow with Soil erosion being a major problem and as a result of this, approximately 50% of the sediment in the river comes from the upper basin. In Yunnan Province in China, the river and its tributaries are confined by narrow, deep gorges. The tributary river systems in this part of

15232-572: The total flow has entered the Mekong system. The focus turns from hydrology and water discharge to the assessment of water level, over- bank storage and flooding and the hydrodynamics that determine the timing, duration and volume of the seasonal flow reversal into and out of the Great Lake. Reach 6: Phnom Penh to the South China Sea . Here the mainstream divides into a complex and increasingly controlled and artificial system of branches and canals. Key features of flow behaviour are tidal influences and salt water intrusion. Every year, 35–50% of this reach

15360-616: The tripoint of Myanmar, Laos, and Thailand . This is also the point of confluence between the Ruak River (which follows the Thai–Myanmar border) and the Mekong. The area of this tripoint is sometimes termed the Golden Triangle , although the term also refers to the much larger area of those three countries that was notorious as a drug producing region. From the Golden Triangle tripoint, the Mekong turns southeast to briefly form

15488-478: The underlying geological structure is fairly homogeneous and stable, exerting little or no control on river morphology . In marked contrast, the tributary networks of the Salween , Yangtze , and particularly the Mekong, are complex with different sub-basins often exhibiting different, and distinct, drainage patterns. These complex drainage systems have developed in a setting where the underlying geological structure

15616-687: The use and care of the Mekong. In 1996 China and Myanmar became "dialogue partners" of the MRC and the six countries now work together in a cooperative framework. In 2000, the governments of China, Laos, Thailand and Myanmar signed a Agreement on Commercial Navigation on Lancang-Mekong River among the Governments of the People's Republic of China, the Lao People's Democratic Republic, the Union of Myanmar and

15744-419: The vegetation does not. Shifting cultivation is common in the uplands of northern Laos and is reported to account for as much as 27% of the total land under rice cultivation. As elsewhere in the basin, forest cover has been steadily reduced during the last three decades by shifting agriculture and permanent agriculture. The cumulative impacts of these activities on the river regime have not been measured. However,

15872-464: The wars in Indochina in the 1970s, a significant quantity of explosives (sometimes, entire barges loaded with military ordnance ) sank in the Cambodian section of the Mekong (as well as in the country's other waterways). Besides being a danger for fishermen, unexploded ordnance also creates problems for bridge and irrigation systems construction. As of 2013, Cambodian volunteers are being trained, with

16000-719: The west side of Thakhek. It is 8 kilometres (5.0 mi) from the city, on Route 13. It extends from the Namdone River and its total length is about 15 kilometres (9.3 mi). Some sections of the wall are seen in Thakhek also. Its construction is attributed to the period of the Sikhottabong Empire in the 19th century and is now proposed to be preserved as a national heritage site. Other attractions include: Tad Kham Waterfall (about 52 kilometers from Thakhek District), Tad Nam Khengkam Waterfall (about 37 km to

16128-540: The wild. It is difficult to define a species in a way that applies to all organisms. The debate about species concepts is called the species problem. The problem was recognised even in 1859, when Darwin wrote in On the Origin of Species : I was much struck how entirely vague and arbitrary is the distinction between species and varieties. He went on to write: No one definition has satisfied all naturalists; yet every naturalist knows vaguely what he means when he speaks of

16256-481: Was constructed largely through fluvial and tidal processes. At this time the delta was advancing at a rate of 17 to 18 m (56 to 59 ft) per year. After 3.5 ka, however, the delta had built out beyond the embayment and became subject to wave action and marine currents. These deflected deposition south-eastwards in the direction of the Cà Mau Peninsula , which is one of the most recent features of

16384-542: Was that the Mekong had too many falls and rapids to ever be useful for navigation . The river's source was found by Pyotr Kuzmich Kozlov in 1900. From 1893, the French extended their control of the river into Laos, establishing French Indochina by the first decade of the 20th century. This lasted until the First and Second Indochina Wars expelled French from its former colony and defeated US-supported governments. During

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