Relict (biology)

Content sourced from Wikipedia, licensed under CC BY-SA 3.0.

In biology, a relict is a population or species that used to be widespread or diverse but now survives in a small, isolated patch of habitat. A relictual population is a population that is currently restricted to a limited area, even though it once ranged widely. A relictual taxon is the last living representative of a group that was once common.

Relicts can persist as remnants of what was once widespread and varied. This situation, called relictualism, happens when a broad habitat or range shrinks and only a small, suitable area remains. The rest of the population may disappear or evolve into different forms. Relicts are different from endemics, because endemics are native to a place, not necessarily remnants of a broader former range.

Relicts arise from many causes, including climate changes (like ice ages), competition from other species, geological movements, or changing environments. A relict that still looks like its ancient ancestors in the fossil record but is alive today is sometimes called a living fossil. An evolutionary relict is a species that was common in one time period and persisted into a later time, while much of its ecosystem changed around it.

Examples:
- The thylacine of Tasmania was the last surviving member of a group that once lived on the Australian mainland.
- Omma, a beetle genus with a 200-million-year fossil history, today has a single living species in Australia.
- Pholadomya, a common Mesozoic clam, is now represented by a rare living species in the Caribbean.
- The tuatara of New Zealand is the only living member of its ancient reptile order, Rhynchocephalia, with a fossil record going back about 240 million years.
- Nimravidae were once widespread carnivores; a Miocene European specimen would be a last remnant of that group.
- On the Pribilof and St. Lawrence Islands off Alaska, shrews appear to be relicts of a time when those lands were connected to the mainland.

In plants and broader ecology:
- The Snowdon lily in Wales is an ice-age relict, growing on north-facing slopes of Snowdonia. Its Welsh population is very small and climate change could threaten it.
- Ginkgo biloba is a famous ancient tree that survives today with a wide distribution in cities around the world, even though its ancestors were once widespread.
- The Saimaa ringed seal lives only in Finland’s Saimaa lake system and has a small, vulnerable population.
- The relict leopard frog once ranged across several western states in the U.S. but now survives only in limited desert basins.

Relictual populations are often insular, meaning they are confined to small areas with little chance of movement between groups. This makes them especially vulnerable to disease, inbreeding, habitat loss, invasive species, and climate change. Islands and isolated mountains—so-called sky islands—can protect relicts but also reduce overall species richness and limit dispersal.

Because small, isolated relicts may face extinction, conservation sometimes uses assisted migration or translocation to move narrowly endangered species to safer habitats. Examples include the western swamp tortoise in Australia and the Florida torreya in the United States. Public interest has sometimes helped protect relicts, as with the Wollemi pine (Wollemia nobilis) in Australia, whose discovery led to global propagation to reduce pressure on wild populations.

Other times plants are called relics of cultivation: species once grown by people for medicine, food, dyes, or other uses that have since become rare in the wild or only known from archaeological sites.