biogeography Biogeography is the study of the distribution of species and ecosystems in geographic space and through geological time. Organisms and biological communities often vary in a regular fashion along geographic gradients of latitude, elevation, ...

and

paleontology Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...

, a relict is a

population Population typically refers to the number of people in a single area, whether it be a city or town, region, country, continent, or the world. Governments typically quantify the size of the resident population within their jurisdiction using a ...

taxon In biology, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular nam ...

of organisms that was more widespread or more diverse in the past. A relictual population is a population currently inhabiting a restricted area whose

range Range may refer to: Geography * Range (geographic), a chain of hills or mountains; a somewhat linear, complex mountainous or hilly area (cordillera, sierra) ** Mountain range, a group of mountains bordered by lowlands * Range, a term used to i ...

was far wider during a previous

geologic epoch The geologic time scale, or geological time scale, (GTS) is a representation of time based on the rock record of Earth. It is a system of chronological dating that uses chronostratigraphy (the process of relating strata to time) and geochronol ...

. Similarly, a relictual taxon is a taxon (e.g. species or other lineage) which is the sole surviving representative of a formerly diverse group.

Definition

A relict (or relic) plant or animal is a

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 Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found elsew ...

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 is a rivalry where two or more parties strive for a common goal which cannot be shared: where one's gain is the other's loss (an example of which is a zero-sum game). Competition can arise between entities such as organisms, indivi ...

from other organisms, continental drift, or

climate change In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to E ...

such as an

ice age An ice age is a long period of reduction in the temperature of Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. Earth's climate alternates between ice ages and gree ...

. When a relict is representative of taxa found in the

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

record, and yet is still living, such an organism is sometimes referred to as a

living fossil A living fossil is an extant taxon that cosmetically resembles related species known only from the fossil record. To be considered a living fossil, the fossil species must be old relative to the time of origin of the extant clade. Living fossi ...

. 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.

Examples

A notable example is the

thylacine The thylacine ( , or , also ) (''Thylacinus cynocephalus'') is an extinct carnivorous marsupial that was native to the Australian mainland and the islands of Tasmania and New Guinea. The last known live animal was captured in 1930 in Tasman ...

of Tasmania, a relict

marsupial Marsupials are any members of the mammalian infraclass Marsupialia. All extant marsupials are endemic to Australasia, Wallacea and the Americas. A distinctive characteristic common to most of these species is that the young are carried in a po ...

carnivore that survived into modern times on an island whereas the rest of its species on mainland Australia had gone extinct between 3000 and 2000 years ago. Another example is '' Omma,'' a genus of beetle with a fossil record extending back over 200 million years to the Late Triassic and found worldwide during the Jurassic and Cretaceous, now confined to a single living species in Australia. Another relic from the Triassic is ''

Pholadomya ''Pholadomya'' is a genus of saltwater clams, marine bivalve molluscs in the family Pholadomyidae. Fossils species within this genus lived during the Mesozoic era, in the opening South Atlantic, between present-day Brazil and Africa. In the Tria ...

'', a common clam genus during the Mesozoic, now confined to a single rare species in the Caribbean. An example from the fossil record would be a specimen of

Nimravidae Nimravidae is an extinct family (biology), family of carnivorans, sometimes known as false saber-toothed cats, whose fossils are found in North America and Eurasia. Not considered to belong to the true cats (family Felidae), the nimravids are gen ...

, an extinct branch of carnivores in the mammalian evolutionary tree, if said specimen came from Europe in the

Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...

epoch. 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 The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but the ...

, 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 Speciation is the evolutionary process by which populations evolve to become distinct species. The biologist Orator F. Cook coined the term in 1906 for cladogenesis, the splitting of lineages, as opposed to anagenesis, phyletic evolution within ...

. In

botany Botany, also called , plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist who specialises in this field. The term "botany" comes from the Ancient Greek w ...

, 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 or Eryri (), is a mountainous region in northwestern 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 It was a commonly held belief that the nam ...

, 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. While the extirpation of a geographically

disjunct population In biology, a taxon with a disjunct distribution is one that has two or more groups that are related but considerably separated from each other geographically. The causes are varied and might demonstrate either the expansion or contraction of a s ...

of a relict species may be of regional conservation concern, outright extinction at the species level may occur in this century of rapid

if geographic range occupied by a relict species has already contracted to the degree that it is narrowly

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found elsew ...

. For this reason, the traditional conservation tool of translocation has recently been reframed as

assisted migration According to ''A Dictionary of Ecology'', assisted migration is "the intentional establishment of populations or meta-populations beyond the boundary of a species' historic range for the purpose of tracking suitable habitats through a period of c ...

of narrowly endemic, critically endangered species that are already (or soon expected) to experience climate change beyond their levels of tolerance. Two examples of critically endangered relict species for which assisted migration projects are already underway are the

western swamp tortoise The western swamp turtle or western swamp tortoise (''Pseudemydura umbrina'') is a critically endangered species of freshwater turtle endemic to a small portion of Western Australia. It is the only member of the genus ''Pseudemydura'' in the mon ...

of Australia and a subcanopy conifer tree in the United States called

Florida Torreya ''Torreya taxifolia'', commonly known as Florida torreya or stinking-cedar, but also sometimes as Florida nutmeg or gopher wood, is an endangered subcanopy tree of the yew family, Taxaceae. It is native to only a small glacial refugium in the s ...

. A well-studied botanical example of a relictual taxon is ''

Ginkgo biloba ''Ginkgo biloba'', commonly known as ginkgo or gingko ( ), also known as the maidenhair tree, is a species of tree native to China. It is the last living species in the order Ginkgoales, which first appeared over 290 million years ago. Fossils ...

'', the last living representative of

Ginkgoales Ginkgoales are a gymnosperm order containing only one extant species: ''Ginkgo biloba'', the ginkgo tree. It is monotypic, (the only taxon) within the class Ginkgoopsida, which itself is monotypic within the division Ginkgophyta . The order incl ...

that is restricted to China in the wild. ''Ginkgo'' trees had a diverse and widespread northern distribution during the

Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceo ...

, but are not known from the fossil record after the

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58 The

Saimaa ringed seal The Saimaa ringed seal (''Pusa hispida saimensis'', Finnish: ''Saimaannorppa'') is a subspecies of ringed seal (''Pusa hispida''). They are among the most endangered seals in the world, having a total population of only about 400 individuals. The ...

(''Phoca hispida saimensis'') is an endemic subspecies, a relict of last ice age that lives only in

Finland Finland ( fi, Suomi ; sv, Finland ), officially the Republic of Finland (; ), is a Nordic country in Northern Europe. It shares land borders with Sweden to the northwest, Norway to the north, and Russia to the east, with the Gulf of B ...

in the landlocked and fragmented Saimaa freshwater lake complex. Nowadays the population has less than 400 individuals, which poses a threat to its survival. Another example is the

relict leopard frog The relict leopard frog (''Lithobates onca'') is a species of frog in the family Ranidae, endemic to the United States. It is found along the Colorado river in extreme northwestern Arizona, and adjacent Nevada and southwestern Utah, although its ...

once found throughout

Nevada Nevada ( ; ) is a U.S. state, state in the Western United States, Western region of the United States. It is bordered by Oregon to the northwest, Idaho to the northeast, California to the west, Arizona to the southeast, and Utah to the east. N ...

Arizona Arizona ( ; nv, Hoozdo Hahoodzo ; ood, Alĭ ṣonak ) is a state in the Southwestern United States. It is the 6th largest and the 14th most populous of the 50 states. Its capital and largest city is Phoenix. Arizona is part of the Fou ...

Utah Utah ( , ) is a state in the Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its south by Arizona, and to it ...

, and

Colorado Colorado (, other variants) is a state in the Mountain West subregion of the Western United States. It encompasses most of the Southern Rocky Mountains, as well as the northeastern portion of the Colorado Plateau and the western edge of t ...

, but now only found at Lake Mead National Recreation Area in Nevada and Arizona.

Relevance

The concept of relictualism is useful in understanding the ecology and

conservation status The conservation status of a group of organisms (for instance, a species) indicates whether the group still exists and how likely the group is to become extinct in the near future. Many factors are taken into account when assessing conservation ...

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 is the termination of a kind of organism or of a group of kinds (taxon), usually 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 ...

, such as disease,

inbreeding Inbreeding is the production of offspring from the mating or breeding of individuals or organisms that are closely related genetically. By analogy, the term is used in human reproduction, but more commonly refers to the genetic disorders and o ...

habitat destruction Habitat destruction (also termed habitat loss and habitat reduction) is the process by which a natural habitat becomes incapable of supporting its native species. The organisms that previously inhabited the site are displaced or dead, thereby ...

, competition from

introduced species An introduced species, alien species, exotic species, adventive species, immigrant species, foreign species, non-indigenous species, or non-native species is a species living outside its native distributional range, but which has arrived there ...

, and

global warming In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to E ...

. 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 The African river martin (''Pseudochelidon eurystomina'') is a passerine bird, one of two members of the river martin subfamily of the swallow family, Hirundinidae. When discovered, it was not initially recognised as a swallow, and its structura ...

, also very localized in central Africa. These two species are the only known 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 topography is characterized by alternating parallel mountain ranges and valleys. It is a result of crustal extension due to mantle upwelling, gravitational collapse, crustal thickening, or relaxation of confining stresses. The e ...

topography creates areas that are insular in nature, such as forested mountains surrounded by inhospitable desert, called sky islands. Such situations can serve as refuges for certain

Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...

relicts, such as

Townsend's pocket gopher Townsend's pocket gopher (''Thomomys townsendii'') is a species of pocket gopher endemic to the northwestern United States. Description Townsend's pocket gopher is a relatively large gopher, measuring in total length, including a tail long. Ad ...

, while at the same time creating barriers for

biological dispersal Biological dispersal refers to both the movement of individuals (animals, plants, fungi, bacteria, etc.) from their birth site to their breeding site ('natal dispersal'), as well as the movement from one breeding site to another ('breeding dis ...

. 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 Habitat fragmentation describes the emergence of discontinuities (fragmentation) in an organism's preferred environment (habitat), causing population fragmentation and ecosystem decay. Causes of habitat fragmentation include geological processes ...

can also lead to the insularization of stranded populations. So-called "relics of cultivation"Celka Z., Drapikowska M. 2008
Relics of cultivation in Central Europe: ''Malva alcea'' L. as an example.
Vegetation History and Archaeobotany. Volume 17, Supplement 1, 251-255, 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.

References

{{Reflist Biogeography

Definition

Examples

Relevance

See also

References