A relict is a surviving remnant of a natural phenomenon.
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In biogeography, paleontology, and other disciplines concerned with the evolutionary 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.[1] 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 carnivores 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.[2]
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.[3]
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.[4] 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.[5]
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,[3] 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.[1][6]
So-called "relics of cultivation" [7] 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.
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 permafrost is an area of ancient permafrost which remains despite a change in climate which would prohibit new permafrost from forming.[8] 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.[9]
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.[10]
In various places around the world, minority ethnic groups represent lineages of ancient human migrations 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.[11]
An example of a linguistic relict is the Romansh language, an official language in provincial Switzerland.[12]