User:Snowboots11/Glacial relict

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A glacial relict is a population of a species previously common during a glacial period that retreated into refugia during interglacial periods. They are typically cold-adapted species with a distribution restricted to regions and microhabitats that allow them to survive despite climatic changes.

A true glacial relict (as opposed to a species displaying relict-like qualities) should have a range limited to refugia that represent microhabitats of its formerly expansive Pleistocene range. Some extant species may resemble glacial relicts, but lack the biogeographical history of relicts, i.e. their range was already limited to habitats resembling those of their current distribution during the Pleistocene, or their restricted habitats developed after the Pleistocene/Holocene transition.

Origin of the term
Charlotte Holmquist recounts the history of the glacial/post-glacial relict concept in The Relict Concept: Is It a Merely Zoogeographical Conception? She reveals that while terms like "relict" or similar were used to name individual species since at least the early 1800s, work exploring the glacial relict concept blossomed after lectures and a series of papers on post-glacial northern Europe by Sven Ludvig Lovén. By 1859 Darwin wrote of “Dispersal during the Glacial Period” in the vastly influential On the Origin of Species. Immediate interest focused on ancient lakes host to clearly unique species assemblages compared to neighboring lakes (the example of Baikal is given). Since the early 1900s, use of the term “relict” in biology has been split between a general definition focusing on isolation from a larger population by changed conditions (see “Relict (biology)”), and a more specific “glacial” definition with specificity to population isolation occurring at the end of the last ice age.

Dítě et al. (2018) note that while the concept has had no set definition and lost its validity as a subject of study due to difficulties in obtaining empirical evidence for glacial relict status, the field is popularizing once again due to phylogeographical and paleoecological advancements that make it possible to directly assess relict-status. Central to the question of a particular species status as a glacial relict or not is its comparative abundance during glacial periods, and its low abundance and geographic isolation to refugia during interglacial periods.

Relict Communities

 * The biogeography of various aquatic species deemed glacial relicts that are found in Lake Sommen is likely related to a different geography during the early history of the lake. One theory claims that aquatic species were transferred from the Baltic Ice Lake through a natural lock system in connection with a temporary advance of the ice-front during the Younger Dryas. On land, the unusual occurrence of dwarf birch near Sund is also judged to be a leftover from a cold geological past.
 * Some fish species of the northern Baltic sea, namely eelpout (Zoarces viviparus), lumpfish (Cyclopterus lumpus) and fourhorned sculpin (Myoxocephalus quadricornis), have been deemed glacial relicts, relying on deep, highly oxygenated cold waters that would have been more expansive environments during the last glacial period.
 * The arctic-alpine Salix hastata and boreo-atlantic Juncus balticus both survived glacial retreats at the end of the Pleistocene in calcareous fens within the Iberian peninsula.
 * Reindeer/caribou (Rangifer tarandus) survived in Central European, no-analog relict communities for about 3,000 years during the Pleistocene/Holocene transition.