In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring by sexual reproduction. Other ways of defining species include their karyotype, DNA sequence, behaviour or ecological niche. In addition, paleontologists use the concept of the chronospecies since fossil reproduction cannot be examined. While these definitions may seem adequate, when looked at more they represent problematic species concepts. For example, the boundaries between related species become unclear with hybridisation, in a species complex of hundreds of similar microspecies, in a ring species. Among organisms that reproduce only asexually, the concept of a reproductive species breaks down, each clone is a microspecies. All species are given a two-part name, a "binomial"; the first part of a binomial is the genus.
The second part is called the specific epithet. For example, Boa constrictor is one of four species of the genus Boa. None of these is satisfactory definitions, but scientists and conservationists need a species definition which allows them to work, regardless of the theoretical difficulties. If species were fixed and distinct from one another, there would be no problem, but evolutionary processes cause species to change continually, to grade into one another. Species were seen from the time of Aristotle until the 18th century as fixed kinds that could be arranged in a hierarchy, the great chain of being. In the 19th century, biologists grasped. Charles Darwin's 1859 book The Origin of Species explained how species could arise by natural selection; that understanding was 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. Viruses are a special case, driven by a balance of mutation and selection, 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 formalised as the typological or morphological species concept. Ernst Mayr emphasised reproductive isolation, but this, like other species concepts, is hard or impossible to test. 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, the philosopher of science John Wilkins counted 26. Wilkins further grouped the species concepts into seven basic kinds of concepts: agamospecies for asexual organisms biospecies for reproductively isolated sexual organisms ecospecies based on ecological niches evolutionary species based on lineage genetic species based on gene pool morphospecies based on form or phenotype and taxonomic species, a species as determined by a taxonomist.
A typological species is a group of organisms in which individuals conform to certain fixed properties, so that pre-literate people recognise the same taxon as do modern taxonomists. The clusters of variations or phenotypes within specimens would differentiate the species; this method was used as a "classical" method of determining species, such as with Linnaeus early in evolutionary theory. However, different phenotypes are not different species. Species named in this manner are called morphospecies. In the 1970s, Robert R. Sokal, Theodore J. Crovello and Peter Sneath proposed a variation on this, 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 is a group of sexually reproducing organisms that recognize 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. A further development of the recognition concept is provided by the biosemiotic concept of species. In microbiology, genes can move even between distantly related bacteria extending to the whole bacterial domain; as a rule of thumb, microbiologists have assumed that kinds 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 the same species or not. This concept was narrowed in 2006 to a similarity of 98.7%. DNA-DNA hybri
In ecology, a habitat is the type of natural environment in which a particular species of organism lives. It is characterized by both biological features. A species' habitat is those places where it can find food, shelter and mates for reproduction; the physical factors are for example soil, range of temperature, light intensity as well as biotic factors such as the availability of food and the presence or absence of predators. Every organism has certain habitat needs for the conditions in which it will thrive, but some are tolerant of wide variations while others are specific in their requirements. A habitat is not a geographical area, it can be the interior of a stem, a rotten log, a rock or a clump of moss, for a parasitic organism it is the body of its host, part of the host's body such as the digestive tract, or a single cell within the host's body. Habitat types include polar, temperate and tropical; the terrestrial vegetation type may be forest, grassland, semi-arid or desert. Fresh water habitats include marshes, rivers and ponds, marine habitats include salt marshes, the coast, the intertidal zone, reefs, the open sea, the sea bed, deep water and submarine vents.
Habitats change over time. This may be due to a violent event such as the eruption of a volcano, an earthquake, a tsunami, a wildfire or a change in oceanic currents. Other changes come as a direct result of human activities; the introduction of alien species can have a devastating effect on native wildlife, through increased predation, through competition for resources or through the introduction of pests and diseases to which the native species have no immunity. The word "habitat" has been in use since about 1755 and derives from the Latin habitāre, to inhabit, from habēre, to have or to hold. Habitat can be defined as the natural environment of an organism, the type of place in which it is natural for it to live and grow, it is similar in meaning to a biotope. The chief environmental factors affecting the distribution of living organisms are temperature, climate, soil type and light intensity, the presence or absence of all the requirements that the organism needs to sustain it. Speaking, animal communities are reliant on specific types of plant communities.
Some plants and animals are generalists, their habitat requirements are met in a wide range of locations. The small white butterfly for example is found on all the continents of the world apart from Antarctica, its larvae feed on a wide range of Brassicas and various other plant species, it thrives in any open location with diverse plant associations. The large blue butterfly is much more specific in its requirements. Disturbance is important in the creation of biodiverse habitats. In the absence of disturbance, a climax vegetation cover develops that prevents the establishment of other species. Wildflower meadows are sometimes created by conservationists but most of the flowering plants used are either annuals or biennials and disappear after a few years in the absence of patches of bare ground on which their seedlings can grow. Lightning strikes and toppled trees in tropical forests allow species richness to be maintained as pioneering species move in to fill the gaps created. Coastal habitats can become dominated by kelp until the seabed is disturbed by a storm and the algae swept away, or shifting sediment exposes new areas for colonisation.
Another cause of disturbance is when an area may be overwhelmed by an invasive introduced species, not kept under control by natural enemies in its new habitat. Terrestrial habitat types include forests, grasslands and deserts. Within these broad biomes are more specific habitats with varying climate types, temperature regimes, soils and vegetation types. Many of these habitats grade into each other and each one has its own typical communities of plants and animals. A habitat may suit a particular species well, but its presence or absence at any particular location depends to some extent on chance, on its dispersal abilities and its efficiency as a coloniser. Freshwater habitats include rivers, lakes, ponds and bogs. Although some organisms are found across most of these habitats, the majority have more specific requirements; the water velocity, its temperature and oxygen saturation are important factors, but in river systems, there are fast and slow sections, pools and backwaters which provide a range of habitats.
Aquatic plants can be floating, semi-submerged, submerged or grow in permanently or temporarily saturated soils besides bodies of water. Marginal plants provide important habitat for both invertebrates and vertebrates, submerged plants provide oxygenation of the water, absorb nutrients and play a part in the reduction of pollution. Marine habitats include brackish water, bays, the open sea, the intertidal zone, the sea bed and deep / shallow water zones. Further variations include rock pools, sand banks, brackish lagoons and pebbly beaches, seagrass beds, all supporting their own flora and fauna; the benth
Predation is a biological interaction where one organism, the predator and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation and parasitoidism, it is distinct from scavenging on dead prey, though many predators scavenge. Predators may search for prey or sit and wait for it; when prey is detected, the predator assesses. This may involve pursuit predation, sometimes after stalking the prey. If the attack is successful, the predator kills the prey, removes any inedible parts like the shell or spines, eats it. Predators are adapted and highly specialized for hunting, with acute senses such as vision, hearing, or smell. Many predatory animals, both vertebrate and invertebrate, have sharp claws or jaws to grip and cut up their prey. Other adaptations include aggressive mimicry that improve hunting efficiency. Predation has a powerful selective effect on prey, the prey develop antipredator adaptations such as warning coloration, alarm calls and other signals, mimicry of well-defended species, defensive spines and chemicals.
Sometimes predator and prey find themselves in an evolutionary arms race, a cycle of adaptations and counter-adaptations. Predation has been a major driver of evolution since at least the Cambrian period. At the most basic level, predators eat other organisms. However, the concept of predation is broad, defined differently in different contexts, includes a wide variety of feeding methods. A parasitoid, such as an ichneumon wasp, lays its eggs on its host. Zoologists call this a form of parasitism, though conventionally parasites are thought not to kill their hosts. A predator can be defined to differ from a parasitoid in two ways: it kills its prey immediately. There are other borderline cases. Micropredators are small animals that, like predators, feed on other organisms. However, since they do not kill their hosts, they are now thought of as parasites. Animals that graze on phytoplankton or mats of microbes are predators, as they consume and kill their food organisms. However, when animals eat seeds or eggs, they are consuming entire living organisms, which by definition makes them predators, albeit unconventional ones: for instance, a mouse that eats grass seeds has no adaptations for tracking and subduing prey and its teeth are not adapted to slicing through flesh.
Scavengers, organisms that only eat organisms found dead, are not predators, but many predators such as the jackal and the hyena scavenge when the opportunity arises. Among invertebrates, social wasps are both scavengers of other insects. While examples of predators among mammals and birds are well known, predators can be found in a broad range of taxa, they are common among insects, including mantids, dragonflies and scorpionflies. In some species such as the alderfly, only the larvae are predatory. Spiders are predatory, as well as other terrestrial invertebrates such as scorpions. In marine environments, most cnidarians, ctenophora and flatworms are predatory. Among crustaceans, crabs and barnacles are predators, in turn crustaceans are preyed on by nearly all cephalopods. Seed predation is restricted to mammals and insects and is found in all terrestrial ecosystems. Egg predation includes both specialist egg predators such as some colubrid snakes and generalists such as foxes and badgers that opportunistically take eggs when they find them.
Some plants, like the pitcher plant, the Venus fly trap and the sundew, are carnivorous and consume insects. Some carnivorous fungi catch nematodes using either active traps in the form of constricting rings, or passive traps with adhesive structures. Many species of protozoa and bacteria prey on other microorganisms. Among freshwater and marine zooplankton, whether single-celled or multi-cellular, predatory grazing on phytoplankton and smaller zooplankton is common, found in many species of nanoflagellates, ciliates, rotifers, a diverse range of meroplankton animal larvae, two groups of crustaceans, namely copepods and cladocerans. To feed, a predator must search for and kill its prey; these actions form a foraging cycle. The predator must decide. If it chooses pursuit, its physical capabilities determine the mode of pursuit. Having captured the prey, it may need to expend energy handling it (e.g. killing it, removing any shell or
Ecuador the Republic of Ecuador, is a country in northwestern South America, bordered by Colombia on the north, Peru on the east and south, the Pacific Ocean to the west. Ecuador includes the Galápagos Islands in the Pacific, about 1,000 kilometres west of the mainland; the capital city is Quito, the largest city. What is now Ecuador was home to a variety of Amerindian groups that were incorporated into the Inca Empire during the 15th century; the territory was colonized by Spain during the 16th century, achieving independence in 1820 as part of Gran Colombia, from which it emerged as its own sovereign state in 1830. The legacy of both empires is reflected in Ecuador's ethnically diverse population, with most of its 16.4 million people being mestizos, followed by large minorities of European and African descendants. Spanish is the official language and is spoken by a majority of the population, though 13 Amerindian languages are recognized, including Quichua and Shuar; the sovereign state of Ecuador is a middle-income representative democratic republic with a developing economy, dependent on commodities, namely petroleum and agricultural products.
It is governed as a democratic presidential republic. One of 18 megadiverse countries in the world, Ecuador hosts many endemic plants and animals, such as those of the Galápagos Islands. In recognition of its unique ecological heritage, the new constitution of 2008 is the first in the world to recognize enforceable Rights of Nature, or ecosystem rights, it has the fifth lowest homicide rate in the Americas. Various peoples had settled in the area of the future Ecuador before the arrival of the Incas; the archeological evidence suggests that the Paleo-Indians' first dispersal into the Americas occurred near the end of the last glacial period, around 16,500–13,000 years ago. The first Indians who reached Ecuador may have journeyed by land from North and Central America or by boat down the Pacific Ocean coastline. Much migrations to Ecuador may have come via the Amazon tributaries, others descended from northern South America, others ascended from the southern part of South America through the Andes.
They developed different languages while emerging as unique ethnic groups. Though their languages were unrelated, these groups developed similar groups of cultures, each based in different environments; the people of the coast developed a fishing and gathering culture. Over time these groups began to interact and intermingle with each other so that groups of families in one area became one community or tribe, with a similar language and culture. Many civilizations arose in Ecuador, such as the Valdivia Culture and Machalilla Culture on the coast, the Quitus, the Cañari; each civilization developed its own distinctive architecture and religious interests. In the highland Andes mountains, where life was more sedentary, groups of tribes cooperated and formed villages. Through wars and marriage alliances of their leaders, a group of nations formed confederations. One region consolidated under a confederation called the Shyris, which exercised organized trading and bartering between the different regions.
Its political and military power came under the rule of the Duchicela blood-line. When the Incas arrived, they found that these confederations were so developed that it took the Incas two generations of rulers—Topa Inca Yupanqui and Huayna Capac—to absorb them into the Inca Empire; the native confederations that gave them the most problems were deported to distant areas of Peru and north Argentina. A number of loyal Inca subjects from Peru and Bolivia were brought to Ecuador to prevent rebellion. Thus, the region of highland Ecuador became part of the Inca Empire in 1463 sharing the same language. In contrast, when the Incas made incursions into coastal Ecuador and the eastern Amazon jungles of Ecuador, they found both the environment and indigenous people more hostile. Moreover, when the Incas tried to subdue them, these indigenous people withdrew to the interior and resorted to guerrilla tactics; as a result, Inca expansion into the Amazon Basin and the Pacific coast of Ecuador was hampered.
The indigenous people of the Amazon jungle and coastal Ecuador remained autonomous until the Spanish soldiers and missionaries arrived in force. The Amazonian people and the Cayapas of Coastal Ecuador were the only groups to resist Inca and Spanish domination, maintaining their language and culture well into the 21st century. Before the arrival of the Spaniards, the Inca Empire was involved in a civil war; the untimely death of both the heir Ninan Cuchi and the Emperor Huayna Capac, from a European disease that spread into Ecuador, created a power vacuum between two factions. The northern faction headed by Atahualpa claims that Huayna Capac gave a verbal decree before his death about how the empire should be divided, he gave the territories pertaining to present-day Ecuador and northern Peru to his favorite son Atahualpa, to rule from Quito. He willed that his heart be buried in Quito, his favorite city, the rest of his body be buried with his ancestors in Cuzco. Huáscar did not recognize his fa
Odd-toed ungulates, mammals which constitute the taxonomic order Perissodactyla, are hoofed animals—ungulates—which bear most of their weight on one of the five toes: the third toe. The non-weight-bearing toes are either present, vestigial, or positioned posteriorly. By contrast, the even-toed ungulates bear most of their weight on two of the five toes: their third and fourth toes. Another difference between the two is that odd-toed ungulates digest plant cellulose in their intestines rather than in one or more stomach chambers as the even-toed ungulates do; the order includes about 17 species divided into three families: Equidae and Tapiridae. Despite their different appearances, they were recognized as related families in the 19th century by the zoologist Richard Owen, who coined the order name; the largest odd-toed ungulates are rhinoceroses, the extinct Paraceratherium, a hornless rhino from the Oligocene, is considered one of the largest land mammals of all time. At the other extreme, an early member of the order, the prehistoric horse Hyracotherium, had a withers height of only 30 to 60 cm.
Apart from dwarf varieties of the domestic horse and donkey, perissodactyls reach a body length of 180–420 cm and a weight of 150 to 4,500 kg. While rhinos have only sparse hair and exhibit a thick epidermis and horses have dense, short coats. Most species are brown, although zebras and young tapirs are striped; the main axes of both the front and rear feet pass through the third toe, always the largest. The remaining toes have been reduced in size to varying degrees. Tapirs, which are adapted to walking on soft ground, have four toes on their fore feet and three on their hind feet. Living rhinos have three toes on both the hind feet. Modern equines possess only a single toe. Rhinos and tapirs, by contrast, have hooves covering only the leading edge of the toes, with the bottom being soft; the ulnae and fibulae are reduced in horses. A common feature that distinguishes this group from other mammals is the saddle-shaped ankle between the astragalus and the scaphoid, which restricts the mobility of the foot.
The thigh is short, the clavicle is absent. Odd-toed ungulates have a long upper jaw with an extended diastema between the front and cheek teeth, giving them an elongated head; the various forms of snout between families are due to differences in the form of the premaxilla. The lacrimal bone has projecting cusps in a wide contact with the nasal bone; the temporomandibular joint is high and the mandible is enlarged. Rhinos have one or two horns made of agglutinated keratin, unlike the horns of even-toed ungulates, which have a bony core; the number and form of the teeth vary according to diet. The incisors and canines can be small or absent, as in the two African species of rhinoceros. In the horses only the males possess canines; the surface shape and height of the molars is dependent on whether soft leaves or hard grass makes up the main component of their diets. Three or four cheek teeth are present on each jaw half, so the dental formula of odd-toed ungulates is: 0-3. 0-1. 2-4. 31-3. 1. 2-4. 3 × 2 = 30-44 All perissodactyls are hindgut fermenters.
In contrast to ruminants, hindgut fermenters store digested food that has left the stomach in an enlarged cecum, where the food is digested by bacteria. No gallbladder is present; the stomach of perissodactyls is built, while the cecum accommodates up to 90 l in horses. The intestine is long, reaching up to 26 m in horses. Extraction of nutrients from food is inefficient, which explains why no odd-toed ungulates are small; the present distribution of most perissodactyl species is only a small fraction of their original range. Members of this group are now found only in Central and South America and southern Africa, central and southeastern Asia. During the peak of odd-toed ungulate existence, from the Eocene to the Oligocene, perissodactyls were distributed over much of the globe, the only exceptions being Australia and Antarctica. Horses and tapirs arrived in South America after the formation of the Isthmus of Panama in the Pliocene, around 3 million years ago. In North America, they died out around 10,000 years ago, while in Europe, the tarpans disappeared in the 19th century.
Hunting and habitat restriction have reduced the present-day species to fragmented relict populations. In contrast, domesticated horses and donkeys have gained a worldwide distribution, feral animals of both species are now found in regions outside of their original range, such as in Australia. Perissodactyls inhabit a number of different habitats. Tapirs are solitary and inhabit tropical rainforests. Rhinos tend to live alone in rather dry savannas, in Asia, wet marsh or forest areas. Horses inhabit open areas such as grasslands, steppes, or semi-deserts, live together in groups. Odd-toed ungulates are herbivores that feed, to varying degrees, on grasses and other plant parts. A distinction is made between grass feeders and leaf feeders. Odd-toed ungulates are characterized by a long gestation period and a small litter size delivering a single young; the g
A fern is a member of a group of vascular plants that reproduce via spores and have neither seeds nor flowers. They differ from mosses by being vascular, i.e. having specialized tissues that conduct water and nutrients and in having life cycles in which the sporophyte is the dominant phase. Like other vascular plants, ferns have complex leaves called megaphylls, that are more complex than the microphylls of clubmosses. Most ferns are leptosporangiate ferns, sometimes referred to as true ferns, they produce coiled fiddleheads that expand into fronds. The group includes about 10,560 known extant species. Ferns are defined here in the broad sense, being all of the Polypodiopsida, comprising both the leptosporangiate and eusporangiate ferns, the latter itself comprising ferns other than those denominated true ferns, including horsetails or scouring rushes, whisk ferns, marattioid ferns, ophioglossoid ferns. Ferns first appear in the fossil record about 360 million years ago in the late Devonian period, but many of the current families and species did not appear until 145 million years ago in the early Cretaceous, after flowering plants came to dominate many environments.
The fern Osmunda claytoniana is a paramount example of evolutionary stasis. Ferns are not of major economic importance, but some are used for food, medicine, as biofertilizer, as ornamental plants and for remediating contaminated soil, they have been the subject of research for their ability to remove some chemical pollutants from the atmosphere. Some fern species, such as bracken and water fern are significant weeds world wide; some fern genera, such as Azolla can fix nitrogen and make a significant input to the nitrogen nutrition of rice paddies. They play certain roles in mythology and art. Like the sporophytes of seed plants, those of ferns consist of stems and roots. Stems: Fern stems are referred to as rhizomes though they grow underground only in some of the species. Epiphytic species and many of the terrestrial ones have above-ground creeping stolons, many groups have above-ground erect semi-woody trunks; these can reach up to 20 meters tall in a few species. Leaf: The green, photosynthetic part of the plant is technically a megaphyll and in ferns, it is referred to as a frond.
New leaves expand by the unrolling of a tight spiral called a crozier or fiddlehead fern. This uncurling of the leaf is termed circinate vernation. Leaves are divided into a sporophyll. A trophophyll frond is a vegetative leaf analogous to the typical green leaves of seed plants that does not produce spores, instead only producing sugars by photosynthesis. A sporophyll frond is a fertile leaf that produces spores borne in sporangia that are clustered to form sori. In most ferns, fertile leaves are morphologically similar to the sterile ones, they photosynthesize in the same way. In some groups, the fertile leaves are much narrower than the sterile leaves, may have no green tissue at all; the anatomy of fern leaves can either be simple or divided. In tree ferns, the main stalk that connects the leaf to the stem has multiple leaflets; the leafy structures that grow from the stipe are known as pinnae and are again divided into smaller pinnules. Roots: The underground non-photosynthetic structures that take up water and nutrients from soil.
They are always fibrous and structurally are similar to the roots of seed plants. Like all other vascular plants, the diploid sporophyte is the dominant phase or generation in the life cycle; the gametophytes of ferns, are different from those of seed plants. They are free-living and resemble liverworts, whereas those of seed plants develop within the spore wall and are dependent on the parent sporophyte for their nutrition. A fern gametophyte consists of: Prothallus: A green, photosynthetic structure, one cell thick heart or kidney shaped, 3–10 mm long and 2–8 mm broad; the prothallus produces gametes by means of: Antheridia: Small spherical structures that produce flagellate sperm. Archegonia: A flask-shaped structure that produces a single egg at the bottom, reached by the sperm by swimming down the neck. Rhizoids: root-like structures that consist of single elongated cells, that absorb water and mineral salts over the whole structure. Rhizoids anchor the prothallus to the soil. Ferns first appear in the fossil record in the early Carboniferous period.
By the Triassic, the first evidence of ferns related to several modern families appeared. The great fern radiation occurred in the late Cretaceous, when many modern families of ferns first appeared. Ferns were traditionally classified in the class Filices, in a Division of the Plant Kingdom named Pteridophyta or Filicophyta. Pteridophyta is no longer recognised as a valid taxon; the ferns are referred to as Polypodiophyta or, when treated as a subdivision of Tracheophyta, although this name sometimes only refers to leptosporangiate ferns. Traditionally, all of the spore producing vascular plants were informally denominated the pteridophytes, rendering the term synonymous with ferns and fern allies; this can be confusing because members of the division Pteridophyta were denominated pteridophytes. Traditionally, three discrete groups have be
Venezuela the Bolivarian Republic of Venezuela, is a country on the northern coast of South America, consisting of a continental landmass and a large number of small islands and islets in the Caribbean Sea. The capital and largest urban agglomeration is the city of Caracas, it has a territorial extension of 916,445 km2. The continental territory is bordered on the north by the Caribbean Sea and the Atlantic Ocean, on the west by Colombia, Brazil on the south and Tobago to the north-east and on the east by Guyana. With this last country, the Venezuelan government maintains a claim for Guayana Esequiba over an area of 159,542 km2. For its maritime areas, it exercises sovereignty over 71,295 km2 of territorial waters, 22,224 km2 in its contiguous zone, 471,507 km2 of the Caribbean Sea and the Atlantic Ocean under the concept of exclusive economic zone, 99,889 km2 of continental shelf; this marine area borders those of 13 states. The country has high biodiversity and is ranked seventh in the world's list of nations with the most number of species.
There are habitats ranging from the Andes Mountains in the west to the Amazon basin rain-forest in the south via extensive llanos plains, the Caribbean coast and the Orinoco River Delta in the east. The territory now known as Venezuela was colonized by Spain in 1522 amid resistance from indigenous peoples. In 1811, it became one of the first Spanish-American territories to declare independence, not securely established until 1821, when Venezuela was a department of the federal republic of Gran Colombia, it gained full independence as a country in 1830. During the 19th century, Venezuela suffered political turmoil and autocracy, remaining dominated by regional caudillos until the mid-20th century. Since 1958, the country has had a series of democratic governments. Economic shocks in the 1980s and 1990s led to several political crises, including the deadly Caracazo riots of 1989, two attempted coups in 1992, the impeachment of President Carlos Andrés Pérez for embezzlement of public funds in 1993.
A collapse in confidence in the existing parties saw the 1998 election of former coup-involved career officer Hugo Chávez and the launch of the Bolivarian Revolution. The revolution began with a 1999 Constituent Assembly, where a new Constitution of Venezuela was written; this new constitution changed the name of the country to Bolivarian Republic of Venezuela. The sovereign state is a federal presidential republic consisting of 23 states, the Capital District, federal dependencies. Venezuela claims all Guyanese territory west of the Essequibo River, a 159,500-square-kilometre tract dubbed Guayana Esequiba or the Zona en Reclamación. Venezuela is among the most urbanized countries in Latin America. Oil was discovered in the early 20th century, today, Venezuela has the world's largest known oil reserves and has been one of the world's leading exporters of oil; the country was an underdeveloped exporter of agricultural commodities such as coffee and cocoa, but oil came to dominate exports and government revenues.
The 1980s oil glut led to a long-running economic crisis. Inflation peaked at 100% in 1996 and poverty rates rose to 66% in 1995 as per capita GDP fell to the same level as 1963, down a third from its 1978 peak; the recovery of oil prices in the early 2000s gave. The Venezuelan government under Hugo Chávez established populist social welfare policies that boosted the Venezuelan economy and increased social spending, temporarily reducing economic inequality and poverty in the early years of the regime. However, such populist policies became inadequate, causing the nation's collapse as their excesses—including a uniquely extreme fossil fuel subsidy—are blamed for destabilizing the nation's economy; the destabilized economy led to a crisis in Bolivarian Venezuela, resulting in hyperinflation, an economic depression, shortages of basic goods and drastic increases in unemployment, disease, child mortality and crime. These factors have precipitated the Venezuelan Migrant Crisis where more than three million people have fled the country.
By 2017, Venezuela was declared to be in default regarding debt payments by credit rating agencies. In 2018, the country's economic policies led to extreme hyperinflation, with estimates expecting an inflation rate of 1,370,000% by the end of the year. Venezuela is a charter member of the UN, OAS, UNASUR, ALBA, Mercosur, LAIA and OEI. According to the most popular and accepted version, in 1499, an expedition led by Alonso de Ojeda visited the Venezuelan coast; the stilt houses in the area of Lake Maracaibo reminded the Italian navigator, Amerigo Vespucci, of the city of Venice, Italy, so he named the region Veneziola, or "Little Venice". The Spanish version of Veneziola is Venezuela. Martín Fernández de Enciso, a member of the Vespucci and Ojeda crew, gave a different account. In his work Summa de geografía, he states that the crew found indigenous people who called themselves the Veneciuela. Thus, the name "Venezuela" may have evolved from the native word; the official name was Estado de Venezuela, República de Venezuela, Estados Unidos de Venezuela, a