Relict (biology)

Last updated

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]

Contents

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. Another relict from the Triassic is Pholadomya , 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, 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. [4]

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. [5]

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. [6] 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. [7] 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. [8]

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. [9] [10]

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. [11] Nowadays the population has less than 400 individuals, which poses a threat to its survival. [12]

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. [13]

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, [5] 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] [14]

So-called "relics of cultivation" [15] 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

<i>Ginkgo biloba</i> Species of tree

Ginkgo biloba, commonly known as ginkgo or gingko, also known as the maidenhair tree, is a species of gymnosperm tree native to East Asia. It is the last living species in the order Ginkgoales, which first appeared over 290 million years ago, and fossils very similar to the living species, belonging to the genus Ginkgo, extend back to the Middle Jurassic epoch approximately 170 million years ago. The tree was cultivated early in human history and remains commonly planted, and is widely regarded as a living fossil.

<span class="mw-page-title-main">Biogeography</span> Study of the distribution of species and ecosystems in geographic space and through geological time

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, isolation and habitat area. Phytogeography is the branch of biogeography that studies the distribution of plants. Zoogeography is the branch that studies distribution of animals. Mycogeography is the branch that studies distribution of fungi, such as mushrooms.

This glossary of ecology is a list of definitions of terms and concepts in ecology and related fields. For more specific definitions from other glossaries related to ecology, see Glossary of biology, Glossary of evolutionary biology, and Glossary of environmental science.

<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 record

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">Sky island</span> Geographic or environmental feature

Sky islands are isolated mountains surrounded by radically different lowland environments. The term originally referred to those found on the Mexican Plateau and has extended to similarly isolated high-elevation forests. The isolation has significant implications for these natural habitats. The American Southwest region began warming up between c. 20,000 and 10,000 years BP and atmospheric temperatures increased substantially, resulting in the formation of vast deserts that isolated the sky islands. Endemism, altitudinal migration, and relict populations are some of the natural phenomena to be found on sky islands.

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

Endemism is the state of a species only 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 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.

A relict is a surviving remnant of a natural phenomenon.

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>

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.

<i>Discus macclintocki</i> Species of gastropod

Discus macclintocki is a species of land snail in the family Discidae known commonly as the Iowa Pleistocene snail and Pleistocene disc. It occurs in Iowa and Illinois in the United States. It is a federally listed endangered species.

<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).

<span class="mw-page-title-main">Disjunct distribution</span> Large geographic separation between members of a taxon

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 species' range.

Reserve design is the process of planning and creating a nature reserve in a way that effectively accomplishes the goal of the reserve.

<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.

Island ecology is the study of island organisms and their interactions with each other and the environment. Islands account for nearly 1/6 of earth’s total land area, yet the ecology of island ecosystems is vastly different from that of mainland communities. Their isolation and high availability of empty niches lead to increased speciation. As a result, island ecosystems comprise 30% of the world’s biodiversity hotspots, 50% of marine tropical diversity, and some of the most unusual and rare species. Many species still remain unknown.

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.

Taxon cycles refer to a biogeographical theory of how species evolve through range expansions and contractions over time associated with adaptive shifts in the ecology and morphology of species. The taxon cycle concept was explicitly formulated by biologist E. O. Wilson in 1961 after he surveyed the distributions, habitats, behavior and morphology of ant species in the Melanesian archipelago.

The rescue effect is a phenomenon which was first described by Brown and Kodric-Brown, and is commonly used in metapopulation dynamics and many other disciplines in ecology. This populational process explains how the migration of individuals can increase the persistence of small isolated populations by helping to stabilize a metapopulation, thus reducing the chances of extinction. In other words, immigration can lead to the recolonization of previously extinct patches, promoting the long-term persistence of the network of populations.

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. ↑ 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.
  5. 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.
  6. ↑ Brown, Paul (27 March 2003). "Global warming threatens Snowdonian plant". Guardian. London: Guardian Unlimited . Retrieved 9 April 2011.
  7. ↑ 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.
  8. ↑ 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.
  9. ↑ 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.
  10. ↑ Julie Jalalpour; Matt Malkin; Peter Poon; Liz Rehrmann; Jerry Yu (1997). "Ginkgoales: Fossil Record". University of California, Berkeley . Retrieved 3 June 2008.
  11. ↑ 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.
  12. ↑ "Saimaa Ringed Seal". WWF Finland. Retrieved 2019-01-30.
  13. ↑ Turner, Angela K.; Rose, Chris (1989). Swallows & Martins. Boston: Houghton Mifflin. pp.  5, 34, 85–87. ISBN   978-0-395-51174-9.
  14. ↑ 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.
  15. ↑ 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
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.