Information AboutExtinct |
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, shown here in a 1651 illustration by Jan Savery , is an often-cited1 example of Modern Extinction .]] In Biology and Ecology , extinction is the cessation of existence of a Species or group of Taxa , reducing Biodiversity . The moment of extinction is generally considered to be the death of the last individual of that species (although the Capacity To Breed And Recover may have been lost before this point). Because a species' potential Range may be very large, determining this moment is difficult, and is usually done retrospectively. This difficulty leads to phenomena such as Lazarus Taxa , where a species presumed extinct abruptly "re-appears" (typically in the Fossil Record ) after a period of apparent absence. Through . May 20 1994 . URL accessed July 30 2006 . although some species, called Living Fossil s, survive virtually unchanged for hundreds of millions of years. Only one in a thousand species that have existed remain today. Raup, David M. ''Extinction: Bad Genes or Bad Luck?'' W.W. Norton and Company. New York. 1991. pp.3-6 ISBN 978-0393309270 Prior to the dispersion of humans across the earth, extinction generally occurred at a continuous low rate, . ''The Sixth Extinction : Patterns of Life and the Future of Humankind'' ( ISBN 0-385-46809-1 ). DEFINITION A species becomes extinct when the last existing member of that species dies. Extinction therefore becomes a certainty when there are no surviving individuals that are able to reproduce and create a new generation. A species may become Functionally Extinct when only a handful of individuals survive, which are unable to reproduce due to poor health, age, sparse distribution over a large range, a lack of individuals of both sexes (in Sexually Reproducing species), or other reasons. , which died out after the Carboniferous , likely due to competition from newer plant life.Davis, Paul and Kenrick, Paul. Fossil Plants. Smithsonian Books, Washington D.C. (2004). Morran, Robin, C.; A Natural History of Ferns. Timber Press (2004). ISBN 0-88192-667-1]] Pinpointing the extinction (or Pseudoextinction ) of a species requires a Clear Definition Of That Species . If it is to be declared extinct, the species in question must be uniquely identifiable from any ancestor or daughter species, or from other closely related species. Extinction of a species (or replacement by a daughter species) plays a key role in the Punctuated Equilibrium hypothesis of Stephen Jay Gould and Niles Eldredge . See: Niles Eldredge, ''Time Frames: Rethinking of Darwinian Evolution and the Theory of Punctuated Equilibria'', 1986, Heinemann ISBN 0-434-22610-6 In Ecology , ''extinction'' is often used informally to refer to Local Extinction , in which a species ceases to exist in the chosen area of study, but still exists elsewhere. This phenomenon is also known as extirpation. Local extinctions may be followed by a replacement of the species taken from other locations; Wolf Reintroduction is an example of this. Species which are not extinct are termed Extant . Those that are extant but threatened by extinction are referred to as Threatened or Endangered Species . An important aspect of extinction at the present time are human attempts to preserve critically endangered species, which is reflected by the creation of the 2007 . When possible, modern Zoological institutions attempt to maintain a Viable Population for species preservation and possible future Reintroduction to the wild through use of carefully planned Breeding Program s. The extinction of one species' wild population can have knock-on effects, causing further extinctions. These are also called "chains of extinction"2. Pseudoextinction See Also: Pseudoextinction Descendants may or may not exist for extinct species. Daughter species that evolve from a parent species carry on most of the parent species' Genetic Information , and even though the parent species may become extinct, the daughter species lives on. In other cases, species have produced no new variants, or none that are able to survive the parent species' extinction. Extinction of a parent species where daughter species or subspecies are still alive is also called '' Pseudoextinction ''. Pseudoextinction is difficult to demonstrate unless one has a strong chain of evidence linking a living species to members of a pre-existing species. For example, it is sometimes claimed that the extinct '' Hyracotherium '', which was an ancient animal similar to the Horse , is pseudoextinct, rather than extinct, because there are several Extant species of '' Equus '', including Zebra and Donkeys . However, as fossil species typically leave no genetic material behind, it is not possible to say whether ''Hyracotherium'' actually Evolved Into More Modern Horse Species or simply evolved from a common ancestor with modern horses. Pseudoextinction is much easier to demonstrate for larger taxonomic groups. It is said that Dinosaur s are pseudoextinct, because some of their descendants, the Bird s, survive today. CAUSES , one of several species of Extinct Birds , was hunted to extinction over the course of a few decades.]] was declared extinct in 1937 due to hunting and habitat loss.]] There are a variety of causes that can contribute directly or indirectly to the extinction of a species or group of species. "Just as each species is unique," write Beverly and Stephen Stearns, "so is each extinction... the causes for each are varied — some subtle and complex, others obvious and simple".3 Most simply, any species that is unable to Survive or Reproduce in its environment, and unable to move to a new environment where it can do so, dies out and becomes extinct. Extinction of a species may come suddenly when an otherwise healthy species is wiped out completely, as when Toxic Pollution renders its entire Habitat unlivable; or may occur gradually over thousands or millions of years, such as when a species gradually loses out competition for food to better adapted competitors. Assessing the relative importance of genetic factors compared to environmental ones as the causes of extinction has been compared to the Nature-nurture Debate . The question of whether more extinctions in the Fossil record have been caused by Evolution or by catastrophe is a subject of discussion; Mark Newman, the author of ''Modeling Extinction'' argues for a mathematical model that falls between the two positions.. By contrast, Conservation Biology uses the Extinction Vortex model to classify extinctions by cause. When concerns about Human Extinction have been raised, for example in Sir Martin Rees ' 2003 book '' Our Final Hour '', those concerns lie with the effects of Climate Change or Technological disaster. Currently, environmental groups and some governments are concerned with the extinction of species caused by humanity, and are attempting to combat further extinctions through a variety of 2006 . Genetic and demographic causes Population Genetics and demographic phenomena affect the evolution, and therefore the risk of extinction, of species. Species with Small Populations are much more vulnerable to these types of effects. Limited geographic range is the most important determinant of Genus extinction at background rates but becomes increasingly irrelevant as Mass Extinction arises.4 Natural Selection acts to propagate beneficial genetic traits and eliminate weaknesses. It is nevertheless possible for a deleterious mutation to be spread throughout a population through the effect of Genetic Drift . A diverse or "deep" Gene Pool gives a population a higher chance of surviving an adverse change in conditions. Effects that cause or reward a loss in Genetic Diversity can increase the chances of extinction of a species. Population Bottleneck s can dramatically reduce genetic diversity by severely limiting the number of reproducing individuals and make Inbreeding more frequent. The Founder Effect can cause rapid, individual-based speciation and is the most dramatic example of a population bottleneck. See Also: Extinction Vortex Habitat degradation See Also: Habitat destruction The degradation of a species' Habitat may alter the Fitness Landscape to such an extent that the species is no longer able to survive and becomes extinct. This may occur by direct effects, such as the environment becoming Toxic , or indirectly, by limiting a species' ability to compete effectively for diminished resources or against new competitor species. Habitat degradation through toxicity can kill off a species very rapidly, by killing all living members through Contamination or Sterilizing them. It can also occur over longer periods at lower toxicity levels by affecting life span, reproductive capacity, or competitiveness. Habitat degradation can also take the form of a physical destruction of niche habitats. The widespread destruction of Tropical Rainforest s and replacement with open pastureland is widely cited as an example of this; elimination of the dense forest eliminated the infrastructure needed by many species to survive. For example, a Fern that depends on dense shade for protection from direct sunlight can no longer survive without forest to shelter it. Another example is the destruction of ocean floors by bottom trawling.Clover, Charles. 2004. ''The End of the Line: How overfishing is changing the world and what we eat''. Ebury Press, London. ISBN 0-09-189780-7 Diminished resources or introduction of new competitor species also often accompany habitat degradation. Global Warming has allowed some species to expand their range, bringing unwelcome competition to other species that previously occupied that area. Sometimes these new competitors are predators and directly affect prey species, while at other times they may merely outcompete vulnerable species for limited resources. Vital resources including Water and food can also be limited during habitat degradation, leading to extinction. was last seen on May 15 1989 . Decline In Amphibian Populations is ongoing worldwide.]] Predation, competition, and disease Humans have been transporting 2007 . Coextinction See Also: Coextinction Coextinction refers to the loss of a species due to the extinction of another; for example, the extinction of Parasitic insects following the loss of their hosts. Coextinction can also occur when a species loses its Pollinator , or to Predators in a Food Chain who lose their prey. According to Lian Pih Koh, "Species coextinction is a manifestation of the interconnectedness of organisms in complex ecosystems ... While coextinction may not be the most important cause of species extinctions, it is certainly an insidious one"Koh, Lian Pih. '' Science '', Vol 305, Issue 5690, 1632-1634, 10 September 2004 .. MASS EXTINCTIONS going extinct at any given time, as reconstructed from the Fossil Record . Does not attempt to include recent Holocene Extinction Event .]] See Also: Extinction event There have been at least five mass extinctions in the history of life, and four in the last 3.5 billion years in which many species have disappeared in a relatively short period of geological time. The most recent of these, the Cretaceous–Tertiary extinction event 65 million years ago at the end of the Cretaceous period, is best known for having wiped out the non-avian Dinosaur s, among many other species. Modern mass extinction See Also: Holocene extinction event According to a 1998 survey of 400 biologists conducted by 2007 . More significantly the rate of species extinctions at present is estimated at 100 to 1000 times "background" or average extinction rates in the Evolution ary time scale of planet Earth ;J.H.Lawton and R.M.May, ''Extinction rates'', Oxford University Press, Oxford, UK moreover, this current rate of extinction is thus 10 to 100 times greater than any of the prior mass extinction events in the history of the Earth. HISTORY OF SCIENTIFIC UNDERSTANDING , one of the many extinct dinosaur species. The cause of the Cretaceous–Tertiary Extinction Event is a subject of much debate amongst researchers.]] In the 1800s when extinction was first described, the idea of extinction was threatening to those who held a belief in the Great Chain Of Being , a Theological position that did not allow for "missing links". The possibility of extinction was not widely accepted before the 1800s.Viney, Mike. " Extinction Part 2 of 5 ". and others. HUMAN ATTITUDES AND INTERESTS Extinction is an important research topic in the field of Zoology , and Biology in general, and has also become an area of concern outside the scientific community. A number of organisations, such as the Worldwide Fund For Nature , have been created with the goal of preserving species from extinction. Government s have attempted, through enacting laws, to avoid human overharvesting or habitat destruction. While many human-caused extinctions have been accidental, humans have also engaged in the deliberate destruction of some species, such as dangerous Virus es, and the extirpation of other problematic species has been suggested. Biologist Bruce Walsh of the 2006 .. In modern times, commercial and industrial interests often have to contend with the effects of production on plant and animal life. However, some technologies with minimal, or no, proven harmful effects on '' 2006 .). Biogeographer Jared Diamond notes that while Big Business may label environmental concerns as "exaggerated", and often cause "devastating damage", some corporations find it in their interest to adopt good conservation practices, and even engage in preservation efforts that surpass those taken by National Park s.6 Governments sometimes see the loss of native species as a loss to 2007 . work to educate the public and pressure governments into action. People who live close to nature can be dependent on the survival of all the species in their environment and might be considered some of the people who should be most concerned about extinction risks. However with human Overpopulation in tropical lesser developed countries, there has been enormous pressure on forests due to Subsistence Agriculture and imprudent use of Slash-and-burn agricultural techniques. As a result the indigenous populations often prioritize day-to-day survival over species conservationPaul Ehrlich and Anne Ehrlich, ''Extinction'', Random House, New York (1981) ISBN 0-394-51312-6. Planned extinction Humans have aggressively worked towards the extinction of many species of virus in the cause of disease eradication. For example, the 2007 . l & Mosquito Control Programs offer little realistic hope to the 300 million people in Developing Nation s who will be infected with acute illnesses this year; although trials are ongoing she writes that if they fail: "We should consider the ultimate swatting." 7 Cloning While no extinct species has currently ever been recreated, recent technological advances have encouraged the hypothesis that through the process of . March 9 2001 . URL accessed July 30 2006 . Proposed targets for cloning include the Mammoth and Thylacine , although the latter attempt has been abandoned.8 In order for such a program to succeed, a sufficient number of individuals would need to be cloned (in the case of sexually reproducing organisms) to create a viable population size. The cloning of an extinct species has not yet been attempted, primarily due to technological limitations, though Bioethical and Philosophical objections have also been raised. The concept of cloning extinct species was popularized in the successful novel and movie '' Jurassic Park ''. SEE ALSO
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