Relict
Encyclopedia
A relict is a surviving remnant of a natural phenomenon.
, paleontology
, and other disciplines concerned with the evolution
ary history of plants and animals, a relict population is one found to naturally occur in a restricted area but whose original range
was much larger in a previous geologic epoch
.
To put it another way, a relict (or relic) plant or animal is a taxon
that persists as a remnant of what was once a diverse and widespread population. Relictualism occurs when a widespread habitat or range changes and a small area becomes cut off from the whole. A subset of the population is then confined to the available hospitable area, and survives there while the broader population either shrinks or evolves divergently
. This phenomenon differs from endemism in that the range of the population was not always restricted to the local region. In other words, the species or group did not necessarily arise in that small area, but rather was stranded, or insularized, by changes over time. The agent of change could be anything from competition
from other organisms, continental drift
, or climate change
such as an ice age
.
A notable example is the thylacine
of Tasmania, a relict marsupial
carnivore that survived into modern times on an island whereas most marsupial carnivores elsewhere in the world had long ago gone extinct. When a relict is representative of taxa found in the fossil
record, and yet is still living, such an organism is sometimes referred to as a living fossil
. However, a relict need not be currently living. An evolutionary relict is any organism that was characteristic of the flora or fauna of one age and that persisted into a later age, with the later age being characterized by newly evolved flora or fauna significantly different from those that came before.
An example from the fossil record would be a specimen of Nimravidae
, an extinct branch of carnivore
s in the mammalian evolutionary tree, if said specimen came from Europe in the Miocene
epoch. For if that was the case, the specimen would represent, not the main population, but a last surviving remnant of the nimravid lineage. These carnivores were common and widespread in the previous epoch, the Oligocene
, and disappeared when the climate changed and woodlands were replaced by savanna. They persisted in Europe in the last remaining forests as a relict of the Oligocene: a relict species in a relict habitat.
An example of divergent evolution creating relicts is found in the shrews of the islands off the coast of Alaska, namely the Pribilof Island Shrew
and the St. Lawrence Island Shrew. These species are apparently relicts of a time when the islands were connected to the mainland, and these species were once conspecific with a more widespread species, now the Cinereus Shrew, the three populations having diverged through speciation
.
In botany
, an example of an ice age relict plant population is the Snowdon lily, notable as being precariously rare in Wales. The Welsh population is confined to the north-facing slopes of Snowdonia
, where climatic conditions are apparently similar to ice age Europe. Some have expressed concern that the warming climate will cause the lily to die out in Great Britain. Other populations of the same plant can be found in the Arctic and in the mountains of Europe and North America, where it is known as the common alplily.
The concept of relictualism is useful in understanding the ecology and conservation
status of populations that have become insularized, meaning confined to one small area or multiple small areas with no chance of movement between populations. Insularization makes a population vulnerable to forces that can lead to extinction
, such as disease, inbreeding
, habitat destruction
, competition from introduced species
, and global warming
. Consider the case of the White-eyed River Martin
, a very localized species of bird found only in Southeast Asia, and extremely rare, if not already extinct. Its closest and only surviving living relative is the African River Martin
, also very localized in central Africa. These two species were the only members of the subfamily Pseudochelidoninae, and their widely disjunct populations suggest they are relict populations of a more common and widespread ancestor. Known to science only since 1968, it seems to have disappeared.
Studies have been done on relict populations in isolated mountain and valley habitats in western North America, where the basin and range
topography creates areas that are insular in nature, such as forested mountains surrounded by inhospitable desert, called sky island
s. Such situations can serve as refuges for certain Pleistocene
relicts, such as Townsend's Pocket Gopher
, while at the same time creating barriers for biological dispersal
. Studies have shown that such insular habitats have a tendency toward decreasing species richness
. This observation has significant implications for conservation biology, because habitat fragmentation
can also lead to the insularization of stranded populations.
So-called "relics of cultivation" are plant species that were grown in the past for various purposes (medicinal, food, dyes, etc.), but are no longer utilized. They are naturalized and can be found at archaeological sites etc.
is an area of ancient permafrost which remains despite a change in climate which would prohibit new permafrost from forming. Or it could be a fragment of ancient soil or sediment found in a younger stratum
. A relict sediment
is an area of ancient sediment which remains unburied despite changes in the surrounding environment. In pedology
, the study of soil formation and classification, ancient soil found in the geologic record is called a paleosol
, material formed in the distant past on what was then the surface. A relict paleosol is still found on the surface, and yet is known to have been formed under conditions radically different from the present climate and topography.
In mineralogy
, a relict mineral is a surviving mineral from a parent rock that underwent a destructive or transformative process. For example, serpentinite
is a kind of rock formed in a process called serpentinization, in which a host mineral produces a pseudomorph, and the original mineral is eventually replaced and/or destroyed, but is still present until the process is complete.
s represent lineages of ancient human migration
s in places now home to more populous ethnic groups who arrived later. For example, the first human groups to inhabit the Caribbean islands were hunter-gatherer
tribes from South and Central America. Genetic specimens of natives of Cuba show that, in late pre-Columbian times, the island was home to agriculturalists of Taino
ethnicity, but a relict population of the original hunter-gatherers remained in western Cuba in the form of the Ciboney people.
- In biologyBiologyBiology is a natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy. Biology is a vast subject containing many subdivisions, topics, and disciplines...
a relict (or relic) is an organism that at an earlier time was abundant in a large area but now occurs at only one or a few small areas. - In ecology, an ecosystemEcosystemAn ecosystem is a biological environment consisting of all the organisms living in a particular area, as well as all the nonliving , physical components of the environment with which the organisms interact, such as air, soil, water and sunlight....
which originally ranged over a large expanse, but is now narrowly confined, may be termed a relict. - In geologyGeologyGeology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...
, the term "relict" refers to structures or minerals from a parent rock that did not undergo metamorphosis when the surrounding rock did, or to rock that survived a destructive geologic process. - In agronomyAgronomyAgronomy is the science and technology of producing and using plants for food, fuel, feed, fiber, and reclamation. Agronomy encompasses work in the areas of plant genetics, plant physiology, meteorology, and soil science. Agronomy is the application of a combination of sciences like biology,...
, a relict crop is a crop which was previously grown extensively, but is now only used in one limited region, or a small number of isolated regions. - In historical linguisticsHistorical linguisticsHistorical linguistics is the study of language change. It has five main concerns:* to describe and account for observed changes in particular languages...
, a relict is a word that is a survivor of a form or forms that are otherwise archaic. - A relict was also an ancient term for a widowWidowA widow is a woman whose spouse has died, while a widower is a man whose spouse has died. The state of having lost one's spouse to death is termed widowhood or occasionally viduity. The adjective form is widowed...
, but has come to be a generic or collective term for widows and widowers. - In real estate law, reliction is the gradual recession of water from its usual high water mark so that the newly uncovered land becomes the property of the adjoining riparian property owner.
In biology
In biogeographyBiogeography
Biogeography is the study of the distribution of species , organisms, and ecosystems in space and through geological time. Organisms and biological communities vary in a highly regular fashion along geographic gradients of latitude, elevation, isolation and habitat area...
, paleontology
Paleontology
Paleontology "old, ancient", ὄν, ὀντ- "being, creature", and λόγος "speech, thought") is the study of prehistoric life. It includes the study of fossils to determine organisms' evolution and interactions with each other and their environments...
, and other disciplines concerned with the evolution
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
ary history of plants and animals, a relict population is one found to naturally occur in a restricted area but whose original range
Range (biology)
In biology, the range or distribution of a species is the geographical area within which that species can be found. Within that range, dispersion is variation in local density.The term is often qualified:...
was much larger in a previous geologic epoch
Geologic time scale
The geologic time scale provides a system of chronologic measurement relating stratigraphy to time that is used by geologists, paleontologists and other earth scientists to describe the timing and relationships between events that have occurred during the history of the Earth...
.
To put it another way, a relict (or relic) plant or animal is a taxon
Taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...
that persists as a remnant of what was once a diverse and widespread population. Relictualism occurs when a widespread habitat or range changes and a small area becomes cut off from the whole. A subset of the population is then confined to the available hospitable area, and survives there while the broader population either shrinks or evolves divergently
Divergent evolution
Divergent evolution is the accumulation of differences between groups which can lead to the formation of new species, usually a result of diffusion of the same species to different and isolated environments which blocks the gene flow among the distinct populations allowing differentiated fixation...
. This phenomenon differs from endemism in that the range of the population was not always restricted to the local region. In other words, the species or group did not necessarily arise in that small area, but rather was stranded, or insularized, by changes over time. The agent of change could be anything from competition
Competition (biology)
Competition is an interaction between organisms or species, in which the fitness of one is lowered by the presence of another. Limited supply of at least one resource used by both is required. Competition both within and between species is an important topic in ecology, especially community ecology...
from other organisms, continental drift
Continental drift
Continental drift is the movement of the Earth's continents relative to each other. The hypothesis that continents 'drift' was first put forward by Abraham Ortelius in 1596 and was fully developed by Alfred Wegener in 1912...
, or climate change
Climate change
Climate change is a significant and lasting change in the statistical distribution of weather patterns over periods ranging from decades to millions of years. It may be a change in average weather conditions or the distribution of events around that average...
such as an ice age
Ice age
An ice age or, more precisely, glacial age, is a generic geological period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in the presence or expansion of continental ice sheets, polar ice sheets and alpine glaciers...
.
A notable example is the thylacine
Thylacine
The thylacine or ,also ;binomial name: Thylacinus cynocephalus, Greek for "dog-headed pouched one") was the largest known carnivorous marsupial of modern times. It is commonly known as the Tasmanian tiger or the Tasmanian wolf...
of Tasmania, a relict marsupial
Marsupial
Marsupials are an infraclass of mammals, characterized by giving birth to relatively undeveloped young. Close to 70% of the 334 extant species occur in Australia, New Guinea, and nearby islands, with the remaining 100 found in the Americas, primarily in South America, but with thirteen in Central...
carnivore that survived into modern times on an island whereas most marsupial carnivores elsewhere in the world had long ago gone extinct. When a relict is representative of taxa found in the fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
record, and yet is still living, such an organism is sometimes referred to as a living fossil
Living fossil
Living fossil is an informal term for any living species which appears similar to a species otherwise only known from fossils and which has no close living relatives, or a group of organisms which have long fossil records...
. However, a relict need not be currently living. An evolutionary relict is any organism that was characteristic of the flora or fauna of one age and that persisted into a later age, with the later age being characterized by newly evolved flora or fauna significantly different from those that came before.
An example from the fossil record would be a specimen of Nimravidae
Nimravidae
The Nimravidae, sometimes known as false saber-toothed cats, are an extinct family of mammalian carnivores belonging to the suborder Feliformia and endemic to North America, Europe, and Asia living from the Eocene through the Miocene epochs , existing for approximately .-Morphology:Although some...
, an extinct branch of carnivore
Carnivora
The diverse order Carnivora |Latin]] carō "flesh", + vorāre "to devour") includes over 260 species of placental mammals. Its members are formally referred to as carnivorans, while the word "carnivore" can refer to any meat-eating animal...
s in the mammalian evolutionary tree, if said specimen came from Europe in the Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
epoch. For if that was the case, the specimen would represent, not the main population, but a last surviving remnant of the nimravid lineage. These carnivores were common and widespread in the previous epoch, the Oligocene
Oligocene
The Oligocene is a geologic epoch of the Paleogene Period and extends from about 34 million to 23 million years before the present . As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly...
, and disappeared when the climate changed and woodlands were replaced by savanna. They persisted in Europe in the last remaining forests as a relict of the Oligocene: a relict species in a relict habitat.
An example of divergent evolution creating relicts is found in the shrews of the islands off the coast of Alaska, namely the Pribilof Island Shrew
Pribilof Island Shrew
The Pribilof Island Shrew is a species of mammal in the family Soricidae. It is found only on Alaska's Pribilof Islands.-Further reading:* http://aknhp.uaa.alaska.edu/zoology/pdfs/mammals/Priblof%20Shrew.pdf...
and the St. Lawrence Island Shrew. These species are apparently relicts of a time when the islands were connected to the mainland, and these species were once conspecific with a more widespread species, now the Cinereus Shrew, the three populations having diverged through speciation
Speciation
Speciation is the evolutionary process by which new biological species arise. The biologist Orator F. Cook seems to have been the first to coin the term 'speciation' for the splitting of lineages or 'cladogenesis,' as opposed to 'anagenesis' or 'phyletic evolution' occurring within lineages...
.
In botany
Botany
Botany, plant science, or plant biology is a branch of biology that involves the scientific study of plant life. Traditionally, botany also included the study of fungi, algae and viruses...
, an example of an ice age relict plant population is the Snowdon lily, notable as being precariously rare in Wales. The Welsh population is confined to the north-facing slopes of Snowdonia
Snowdonia
Snowdonia is a region in north Wales and a national park of in area. It was the first to be designated of the three National Parks in Wales, in 1951.-Name and extent:...
, where climatic conditions are apparently similar to ice age Europe. Some have expressed concern that the warming climate will cause the lily to die out in Great Britain. Other populations of the same plant can be found in the Arctic and in the mountains of Europe and North America, where it is known as the common alplily.
The concept of relictualism is useful in understanding the ecology and conservation
Conservation biology
Conservation biology is the scientific study of the nature and status of Earth's biodiversity with the aim of protecting species, their habitats, and ecosystems from excessive rates of extinction...
status of populations that have become insularized, meaning confined to one small area or multiple small areas with no chance of movement between populations. Insularization makes a population vulnerable to forces that can lead to extinction
Extinction
In biology and ecology, extinction is the end of an organism or of a group of organisms , normally a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and recover may have been lost before this point...
, such as disease, inbreeding
Inbreeding
Inbreeding is the reproduction from the mating of two genetically related parents. Inbreeding results in increased homozygosity, which can increase the chances of offspring being affected by recessive or deleterious traits. This generally leads to a decreased fitness of a population, which is...
, habitat destruction
Habitat destruction
Habitat destruction is the process in which natural habitat is rendered functionally unable to support the species present. In this process, the organisms that previously used the site are displaced or destroyed, reducing biodiversity. Habitat destruction by human activity mainly for the purpose of...
, competition from introduced species
Introduced species
An introduced species — or neozoon, alien, exotic, non-indigenous, or non-native species, or simply an introduction, is a species living outside its indigenous or native distributional range, and has arrived in an ecosystem or plant community by human activity, either deliberate or accidental...
, and global warming
Global warming
Global warming refers to the rising average temperature of Earth's atmosphere and oceans and its projected continuation. In the last 100 years, Earth's average surface temperature increased by about with about two thirds of the increase occurring over just the last three decades...
. Consider the case of the White-eyed River Martin
White-eyed River Martin
The White-eyed River Martin is a passerine bird, one of only two members of the river martin subfamily of the swallow family Hirundinidae...
, a very localized species of bird found only in Southeast Asia, and extremely rare, if not already extinct. Its closest and only surviving living relative is the African River Martin
African River Martin
The African River Martin is a passerine bird, one of two members of the river martin subfamily of the swallow family Hirundinidae. It is a medium-sized, mainly black-plumaged species with red eyes, a broad orange-red bill and a square tail...
, also very localized in central Africa. These two species were the only members of the subfamily Pseudochelidoninae, and their widely disjunct populations suggest they are relict populations of a more common and widespread ancestor. Known to science only since 1968, it seems to have disappeared.
Studies have been done on relict populations in isolated mountain and valley habitats in western North America, where the basin and range
Basin and Range
The Basin and Range Province is a vast physiographic region defined by a unique topographic expression. Basin and Range topography is characterized by abrupt changes in elevation, alternating between narrow faulted mountain chains and flat arid valleys or basins...
topography creates areas that are insular in nature, such as forested mountains surrounded by inhospitable desert, called sky island
Sky island
Sky islands are mountains that are isolated by surrounding lowlands of a dramatically different environment, a situation which, in combination with the altitudinal zonation of ecosystems, has significant implications for natural habitats. Endemism, vertical migration, and relict populations are...
s. Such situations can serve as refuges for certain Pleistocene
Pleistocene
The Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....
relicts, such as Townsend's Pocket Gopher
Townsend's Pocket Gopher
Townsend's Pocket Gopher is a species of rodent in the family Geomyidae. It is endemic to the United States....
, while at the same time creating barriers for biological dispersal
Biological dispersal
Biological dispersal refers to species movement away from an existing population or away from the parent organism. Through simply moving from one habitat patch to another, the dispersal of an individual has consequences not only for individual fitness, but also for population dynamics, population...
. Studies have shown that such insular habitats have a tendency toward decreasing species richness
Species richness
Species richness is the number of different species in a given area. It is represented in equation form as S.Species richness is the fundamental unit in which to assess the homogeneity of an environment. Typically, species richness is used in conservation studies to determine the sensitivity of...
. This observation has significant implications for conservation biology, because habitat fragmentation
Habitat fragmentation
Habitat fragmentation as the name implies, describes the emergence of discontinuities in an organism's preferred environment , causing population fragmentation...
can also lead to the insularization of stranded populations.
So-called "relics of cultivation" are plant species that were grown in the past for various purposes (medicinal, food, dyes, etc.), but are no longer utilized. They are naturalized and can be found at archaeological sites etc.
In geology
Some geologic processes are destructive or transformative of structures or minerals, and when a process is not complete or does not completely destroy certain features, the left-over feature is a relict of what was there before. For example, relict permafrostPermafrost
In geology, permafrost, cryotic soil or permafrost soil is soil at or below the freezing point of water for two or more years. Ice is not always present, as may be in the case of nonporous bedrock, but it frequently occurs and it may be in amounts exceeding the potential hydraulic saturation of...
is an area of ancient permafrost which remains despite a change in climate which would prohibit new permafrost from forming. Or it could be a fragment of ancient soil or sediment found in a younger stratum
Stratum
In geology and related fields, a stratum is a layer of sedimentary rock or soil with internally consistent characteristics that distinguish it from other layers...
. A relict sediment
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....
is an area of ancient sediment which remains unburied despite changes in the surrounding environment. In pedology
Pedology
Pedology may refer to:*Pedology *Pedology *Pediatrics...
, the study of soil formation and classification, ancient soil found in the geologic record is called a paleosol
Paleosol
In the geosciences, paleosol can have two meanings. The first meaning, common in geology and paleontology, refers to a former soil preserved by burial underneath either sediments or volcanic deposits , which in the case of older deposits have lithified into rock...
, material formed in the distant past on what was then the surface. A relict paleosol is still found on the surface, and yet is known to have been formed under conditions radically different from the present climate and topography.
In mineralogy
Mineralogy
Mineralogy is the study of chemistry, crystal structure, and physical properties of minerals. Specific studies within mineralogy include the processes of mineral origin and formation, classification of minerals, their geographical distribution, as well as their utilization.-History:Early writing...
, a relict mineral is a surviving mineral from a parent rock that underwent a destructive or transformative process. For example, serpentinite
Serpentinite
Serpentinite is a rock composed of one or more serpentine group minerals. Minerals in this group are formed by serpentinization, a hydration and metamorphic transformation of ultramafic rock from the Earth's mantle...
is a kind of rock formed in a process called serpentinization, in which a host mineral produces a pseudomorph, and the original mineral is eventually replaced and/or destroyed, but is still present until the process is complete.
Of human populations
In various places around the world, minority ethnic groupEthnic group
An ethnic group is a group of people whose members identify with each other, through a common heritage, often consisting of a common language, a common culture and/or an ideology that stresses common ancestry or endogamy...
s represent lineages of ancient human migration
Human migration
Human migration is physical movement by humans from one area to another, sometimes over long distances or in large groups. Historically this movement was nomadic, often causing significant conflict with the indigenous population and their displacement or cultural assimilation. Only a few nomadic...
s in places now home to more populous ethnic groups who arrived later. For example, the first human groups to inhabit the Caribbean islands were hunter-gatherer
Hunter-gatherer
A hunter-gatherer or forage society is one in which most or all food is obtained from wild plants and animals, in contrast to agricultural societies which rely mainly on domesticated species. Hunting and gathering was the ancestral subsistence mode of Homo, and all modern humans were...
tribes from South and Central America. Genetic specimens of natives of Cuba show that, in late pre-Columbian times, the island was home to agriculturalists of Taino
Taíno people
The Taínos were pre-Columbian inhabitants of the Bahamas, Greater Antilles, and the northern Lesser Antilles. It is thought that the seafaring Taínos are relatives of the Arawak people of South America...
ethnicity, but a relict population of the original hunter-gatherers remained in western Cuba in the form of the Ciboney people.