Relict (biology)

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In biogeography and paleontology, a relict is a population or taxon 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 was far wider during a previous geologic epoch. Similarly, a relictual taxon is a taxon (e.g. species or other lineage) which is the sole surviving representative of a formerly diverse group. [1]

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Definition

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.

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.

Examples

The population of the Siberian columbine in the Central Siberian Plateau is considered a quaternary relict. Icones selectae plantarum quas in systemate universali (Tab. 047).jpg
The population of the Siberian columbine in the Central Siberian Plateau is considered a quaternary relict.

A notable example is the thylacine of Tasmania, a relict marsupial 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. [3]

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. [4] Another relict from the Triassic is Pholadomya , a common clam genus during the Mesozoic, now confined to a single rare species in the Caribbean. [5]

The tuatara endemic to New Zealand is the only living member of the once-diverse reptile order Rhynchocephalia, which has a fossil record stretching back 240 million years and during the Mesozoic era was globally distributed and ecologically diverse. [6]

An example from the fossil record would be a specimen of Nimravidae, an extinct branch of carnivores in the mammalian evolutionary tree, if said specimen came from Europe in the Miocene 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, 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. [7]

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. [8]

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. [9] 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 of a relict species may be of regional conservation concern, outright extinction at the species level may occur in this century of rapid climate change if geographic range occupied by a relict species has already contracted to the degree that it is narrowly endemic. For this reason, the traditional conservation tool of translocation has recently been reframed as assisted migration of narrowly endemic, critically endangered species that are already (or soon expected) to experience climate change beyond their levels of tolerance. [10] Two examples of critically endangered relict species for which assisted migration projects are already underway are the western swamp tortoise of Australia and a subcanopy conifer tree in the United States called Florida Torreya. [11]

A well-studied botanical example of a relictual taxon is Ginkgo biloba , the last living representative of Ginkgoales that is restricted to China in the wild. Ginkgo trees had a diverse and widespread northern distribution during the Mesozoic, but are not known from the fossil record after the Pliocene other than G. biloba. [12] [13]

The Saimaa ringed seal (Phoca hispida saimensis) is an endemic subspecies, a relict of last ice age that lives only in Finland in the landlocked and fragmented Saimaa freshwater lake complex. [14] Now the population has less than 400 individuals, which poses a threat to its survival. [15]

Another example is the relict leopard frog once found throughout Nevada, Arizona, Utah, and Colorado, 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 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 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. [16]

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 islands. Such situations can serve as refuges for certain Pleistocene relicts, such as Townsend's pocket gopher, [8] 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. [3] [17]

So-called "relics of cultivation" [18] 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.

See also

Related Research Articles

<span class="mw-page-title-main">Ginkgoales</span> Order of plants

Ginkgoales are a gymnosperm order containing only one extant species: Ginkgo biloba, the ginkgo tree. The order has a long fossil record extending back to the Early Permian around 300 million years ago from fossils found worldwide.

<span class="mw-page-title-main">Tenrec</span> Family of small mammals

A tenrec is a mammal belonging to any species within the afrotherian family Tenrecidae, which is endemic to Madagascar. Tenrecs are a very diverse group; as a result of convergent evolution, some resemble hedgehogs, shrews, opossums, rats, and mice. They occupy aquatic, arboreal, terrestrial, and fossorial environments. Some of these species, including the greater hedgehog tenrec, can be found in the Madagascar dry deciduous forests. However, the speciation rate in this group has been higher in humid forests.

<span class="mw-page-title-main">Living fossil</span> Organism resembling a form long shown in the fossil records

A living fossil is an extant taxon that phenotypically 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 fossils commonly are of species-poor lineages, but they need not be. While the body plan of a living fossil remains superficially similar, it is never the same species as the remote relatives it resembles, because genetic drift would inevitably change its chromosomal structure.

<span class="mw-page-title-main">Lazarus taxon</span> Taxon that disappears from the fossil record, only to reappear later

In paleontology, a Lazarus taxon is a taxon that disappears for one or more periods from the fossil record, only to appear again later. Likewise in conservation biology and ecology, it can refer to species or populations that were thought to be extinct, and are rediscovered. The term Lazarus taxon was coined by Karl W. Flessa and David Jablonski in 1983 and was then expanded by Jablonski in 1986. Paul Wignall and Michael Benton defined Lazarus taxa as, "At times of biotic crisis many taxa go extinct, but others only temporarily disappeared from the fossil record, often for intervals measured in millions of years, before reappearing unchanged". Earlier work also supports the concept though without using the name Lazarus taxon, like work by Christopher R. C. Paul.

<span class="mw-page-title-main">Endemism</span> Species unique to a natural location or habitat

Endemism is the state of a species being found only 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 elsewhere. For example, the Cape sugarbird is found exclusively in southwestern South Africa and is therefore said to be endemic to that particular part of the world. An endemic species can also be referred to as an endemism or, in scientific literature, as an endemite. Similarly many species found in the Western ghats of India are examples of endemism.

<span class="mw-page-title-main">Laysan finch</span> Species of bird

The Laysan finch is a species of Hawaiian honeycreeper, that is endemic to the Northwestern Hawaiian Islands. It is one of four remaining finch-billed Hawaiian honeycreepers and is closely related to the smaller Nihoa finch. The Laysan finch is named for Laysan, the island to which it was endemic on its discovery. It was subsequently introduced to a few other atolls, and its historical range included some of the main islands.

Insular biogeography or island biogeography is a field within biogeography that examines the factors that affect the species richness and diversification of isolated natural communities. The theory was originally developed to explain the pattern of the species–area relationship occurring in oceanic islands. Under either name it is now used in reference to any ecosystem that is isolated due to being surrounded by unlike ecosystems, and has been extended to mountain peaks, seamounts, oases, fragmented forests, and even natural habitats isolated by human land development. The field was started in the 1960s by the ecologists Robert H. MacArthur and E. O. Wilson, who coined the term island biogeography in their inaugural contribution to Princeton's Monograph in Population Biology series, which attempted to predict the number of species that would exist on a newly created island.

<span class="mw-page-title-main">Saimaa ringed seal</span> Freshwater seal found in Finland

The Saimaa ringed seal is a subspecies and glacial relict of ringed seal. They are among the most endangered seals in the world, having a total population of only about 400 individuals. The only existing population of these seals is found in Lake Saimaa, Finland. They have lived in complete isolation from other ringed seal species for around 9,500 years and have diverged into a morphologically and ecologically different subspecies of ringed seal. The population is descended from ringed seals that were separated from the rest when the land rose after the last ice age. This seal, along with the Ladoga seal and the Baikal seal, is one of the few living freshwater seals.

<span class="mw-page-title-main">Refugium (population biology)</span> Ecological concept

In biology, a refugium is a location which supports an isolated or relict population of a once more widespread species. This isolation (allopatry) can be due to climatic changes, geography, or human activities such as deforestation and overhunting.

<span class="mw-page-title-main">Island gigantism</span> Evolutionary phenomena leading to an increase of the size of species with insularity

Island gigantism, or insular gigantism, is a biological phenomenon in which the size of an animal species isolated on an island increases dramatically in comparison to its mainland relatives. Island gigantism is one aspect of the more general "island effect" or "Foster's rule", which posits that when mainland animals colonize islands, small species tend to evolve larger bodies, and large species tend to evolve smaller bodies. This is itself one aspect of the more general phenomenon of island syndrome which describes the differences in morphology, ecology, physiology and behaviour of insular species compared to their continental counterparts. Following the arrival of humans and associated introduced predators, many giant as well as other island endemics have become extinct. A similar size increase, as well as increased woodiness, has been observed in some insular plants such as the Mapou tree in Mauritius which is also known as the "Mauritian baobab" although it is member of the grape family (Vitaceae).

The mammals of Australia have a rich fossil history, as well as a variety of extant mammalian species, dominated by the marsupials, but also including monotremes and placentals. The marsupials evolved to fill specific ecological niches, and in many cases they are physically similar to the placental mammals in Eurasia and North America that occupy similar niches, a phenomenon known as convergent evolution. For example, the top mammalian predators in Australia, the Tasmanian tiger and the marsupial lion, bore a striking resemblance to large canids such as the gray wolf and large cats respectively; gliding possums and flying squirrels have similar adaptations enabling their arboreal lifestyle; and the numbat and anteaters are both digging insectivores. Most of Australia's mammals are herbivores or omnivores.

<span class="mw-page-title-main">Cozumel raccoon</span> Species of critically endangered raccoon

The Cozumel raccoon is a critically endangered species of island raccoon endemic on Cozumel Island off the coast of the Yucatan Peninsula, Mexico. It is sometimes also called the pygmy raccoon, dwarf raccoon, Cozumel Island raccoon, and Cozumel raccoon bear.

<span class="mw-page-title-main">Fauna of Europe</span> Native animals of Europe

The fauna of Europe is all the animals living in Europe and its surrounding seas and islands. Europe is the western part of the Palearctic realm. Lying within the temperate region, the wildlife is not as rich as in the hottest regions, but is nevertheless diverse due to the variety of habitats and the faunal richness of Eurasia as a whole.

<span class="mw-page-title-main">Jenkins's shrew tenrec</span> Species of mammal

Jenkins's shrew tenrec is a species of mammal in the family Tenrecidae. It is endemic to Madagascar. Its natural habitats are subtropical or tropical dry forests and shrubland. It is threatened by habitat loss.

The Michoacan pocket gopher is a species of rodent in the family Geomyidae. It is monotypic within the genus Zygogeomys. It is endemic to Mexico where its natural habitat is temperate, high-altitude forests. Its numbers are declining and it is listed by the IUCN as "endangered".

<i>Asoriculus</i> Extinct genus of red-toothed shrew

Asoriculus is an extinct genus of terrestrial shrews in the subfamily Soricinae and tribe Nectogalini, native to Europe and North Africa, from the Late Miocene until the late Holocene. The genus is closely related and possibly ancestral to the also recently-extinct Balearic shrews (Nesiotites), with their closest living relative being the Himalayan shrew.

<i>Megalenhydris</i> Extinct genus of giant otter

Megalenhydris barbaricina is an extinct species of giant otter from the Late Pleistocene of Sardinia. It is known from a single partial skeleton, discovered in the Grotta di Ispinigoli near Dorgali, and was described in 1987. It was larger than any living otter, exceeding the size of South American giant otters (Petrolutra), which can reach two meters in length. The species is one of four extinct otter species from Sardinia and Corsica. The others are Algarolutra majori, Lutra castiglionis and Sardolutra ichnusae. It is suggested to have ultimately originated from the much smaller European mainland species "Lutra" simplicidens, which may be more closely related to Lutrogale than to modern Lutra species. The structure of the teeth points to a diet of bottom dwelling fish and crustaceans. A special characteristic of the species is the flattening of the first few caudal vertebrae. This might point to a slightly flattened tail.

<span class="mw-page-title-main">Flora of China</span> Collective plants of China

The flora of China consists of a diverse range of plant species including over 39,000 vascular plants, 27,000 species of fungi and 3000 species of bryophytes. More than 30,000 plant species are native to China, representing nearly one-eighth of the world's total plant species, including thousands found nowhere else on Earth. China's land, extending over 9.6 million km, contains a variety of ecosystems and climates for plants to grow in. Some of the main climates include shores, tropical and subtropical forests, deserts, elevated plateaus and mountains. The events of the continental drift and early Paleozoic Caledonian movement also play a part in creating climatic and geographical diversity resulting in high levels of endemic vascular flora. These landscapes provide different ecosystems and climates for plants to grow in, creating a wide variety of different flora spanning over not just China, but different parts of the world.

<span class="mw-page-title-main">Fauna of South Africa</span> Native animals of South Africa

The fauna of South Africa is diverse and largely typical of the ecosystems in Africa. South Africa is ranked sixth out of the world's 17 megadiverse countries. Many endemic species are unique to South Africa. The country is among the world leaders in conservation, but at the time wildlife is threatened by poaching and canned hunting.

<span class="mw-page-title-main">Paleoendemism</span>

Paleoendemism along with neoendemism is a possible subcategory of endemism. Paleoendemism refers to species that were formerly widespread but are now restricted to a smaller area. Neoendemism refers to species that have recently arisen, such as through divergence and reproductive isolation or through hybridization and polyploidy in plants.

References

  1. ↑ Habel, Jan C.; Assmann, Thorsten; Schmitt, Thomas; Avise, John C. (2010). "Relict Species: From Past to Future". In Habel, Jan Christian; Assmann, Thorsten (eds.). Relict species: Phylogeography and Conservation Biology. Berlin: Springer-Verlag. pp. 1–5. ISBN   9783540921608.
  2. ↑ Ziman, Svetlana N.; Keener, Carl S. (1989). "Geographical Analysis of the Family Ranunculaceae". Annals of the Missouri Botanical Garden. 76 (4). Missouri Botanical Garden: 1021. doi:10.2307/2399690. JSTOR   2399690.
  3. 1 2 Quammen, David (2004). The Song of the Dodo: Island Biogeography in An Age of Extinctions. New York: Scribner. pp.  287–288, 436–447, 631. ISBN   978-0-684-82712-4.
  4. ↑ Cai, Chenyang; Huang, Diying (2017-04-03). "Omma daxishanense sp. nov., a fossil representative of an extant Australian endemic genus recorded from the Late Jurassic of China (Coleoptera: Ommatidae)". Alcheringa: An Australasian Journal of Palaeontology. 41 (2): 277–283. doi:10.1080/03115518.2016.1225251. ISSN   0311-5518.
  5. ↑ Morton, Brian; Machado, Fabrizio Marcondes (2019), "Predatory marine bivalves: A review", Advances in Marine Biology, vol. 84, Elsevier, pp. 1–98, doi:10.1016/bs.amb.2019.10.001, ISBN   978-0-12-821794-8 , retrieved 2024-10-04
  6. ↑ Grandcolas, Philippe; Nattier, Romain; Trewick, Steve (December 2014). "Relict species: a relict concept?". Trends in Ecology & Evolution. 29 (12): 655–663. doi:10.1016/j.tree.2014.10.002.
  7. ↑ Prothero, Donald R. (2006). After the Dinosaurs: The Age of Mammals. Bloomington, Indiana: Indiana University Press. pp. 9, 132–134, 160, 174, 176, 198, 222–233. ISBN   978-0-253-34733-6.
  8. 1 2 Wilson, Don; Ruff, Sue (1999). The Smithsonian Book of North American Mammals. Washington, DC: Smithsonian Institution Press. pp.  20, 27–30. ISBN   978-1-56098-845-8.
  9. ↑ Brown, Paul (27 March 2003). "Global warming threatens Snowdonian plant". Guardian. London: Guardian Unlimited . Retrieved 9 April 2011.
  10. ↑ Thomas, Chris D (May 2011). "Translocation of species, climate change, and the end of trying to recreate past ecological communities" (PDF). Trends in Ecology and Evolution. 26 (5): 216–221. doi:10.1016/j.tree.2011.02.006. PMID   21411178.
  11. ↑ Dalrymple, Sarah (16 July 2021). "Why climate change is forcing conservationists to be more ambitious: by moving threatened species to pastures new". The Conversation. Retrieved 26 July 2022.
  12. ↑ Zhou, Zhiyan; Zheng, Shaolin (2003). "Palaeobiology: The missing link in Ginkgo evolution". Nature. 423 (6942): 821–2. Bibcode:2003Natur.423..821Z. doi:10.1038/423821a. PMID   12815417. S2CID   4342303.
  13. ↑ Julie Jalalpour; Matt Malkin; Peter Poon; Liz Rehrmann; Jerry Yu (1997). "Ginkgoales: Fossil Record". University of California, Berkeley . Retrieved 3 June 2008.
  14. ↑ Palo, J.U.; Hyvärinen, H.; Helle, E.; Mäkinen, H.S.; Väinölä, R. (March 2003). "Postglacial loss of microsatellite variation in the landlocked Lake Saimaa ringed seal". Conservation Genetics. 4 (2): 117–128. doi:10.1023/A:1023303109701. eISSN   1572-9737. ISSN   1566-0621. S2CID   25621332.
  15. ↑ "Saimaa Ringed Seal". WWF Finland. Retrieved 2019-01-30.
  16. ↑ Turner, Angela K.; Rose, Chris (1989). Swallows & Martins. Boston: Houghton Mifflin. pp.  5, 34, 85–87. ISBN   978-0-395-51174-9.
  17. ↑ Harris, Larry D. (1984). The Fragmented Forest: Island Biogeography Theory and the Preservation of Biotic Diversity. Chicago: University of Chicago Press. pp.  71–92. ISBN   978-0-226-31763-2.
  18. ↑ 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, doi : 10.1007/s00334-008-0151-0
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