Glacial refugium

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A glacial refugium (plural glacial refugia) is a geographic region which made possible the survival of flora and fauna during ice ages and allowed for post-glacial re-colonization. [1] [2] Different types of glacial refugia can be distinguished, namely nunatak, peripheral, and lowland. [3] Glacial refugia have been suggested as a major cause of floral and faunal distribution patterns in both temperate and tropical latitudes. [4] [5] [6] With respect to disjunct populations of modern-day species, especially in birds, [7] [8] doubt has been cast on the validity of such inferences, as much of the differentiation between populations observed today may have occurred before or after their restriction to refugia. [9] [10] In contrast, isolated geographic locales that host one or more critically endangered species (regarded as paleoendemics or glacial relicts) are generally uncontested as bona fide glacial refugia. [11]

Contents

Identification

Traditionally, the identification of glacial refugia has occurred through palaeoecological analysis, which examines fossil organisms and their remains to determine the origins of modern taxa. [5]  For example, paleoecological approaches have been used to reconstruct the distributions of pollen in Europe for the 13,000 years since the last glaciation. Researchers in this case ultimately established the spread of forest trees from the mountainous southern fringe of Europe, which suggests that this area served as a glacial refugium during this time. [12]

Types

Four distinct types of glacial refugium have been identified:

Hot spring oases

This type of refugium is created by an influx of hydrothermal waters which maintains a humid and warm microclimate that allowed thermophilous trees like oak (Quercus), linden (Tilia), and common ash (Fraxinus excelsior) to survive the last ice age in Central Europe. [13]

Nunatak

A nunatak is a type of glacial refugium that is located on the snow-free, exposed peaks of mountains, which lie above the ice sheet during glaciations. [3] The identification of ‘diversity hotspots’ in areas, which should have been migration regions during major glacial episodes, is evidence for nunatak glacial refugia. [14] For example, the Monte Rosa mountain ranges, the Avers, and the Engadine and the Bernina are all floristically rich proposed nunatak regions, which are indicative nunatak glacial survival. [14]

Peripheral

Like nunataks, peripheral glacial refugia exist within mountain systems; they differ in that they are located at the borders of mountain systems. [3] Evidence for peripheral refugia can be found along the borders of the Carpathian Mountains, Pyrenees, and European Alps, all of which were once glaciated mountain systems. For example, using the amplified fragment length polymorphism (AFLP) technique, researchers have inferred survival of Phyteuma globulariifolium in peripheral refugia in the European Alps. [15]

Lowland

Peak glacial refuges eastern North America.jpg

Lowland glacial refugia, unlike nunatak and peripheral glacial refugia, are found at low elevations rather than in mountains. [3] Situated beyond the limits of ice shields, lowland refugia have been identified for a number of plant and animal species. In Europe, for example, researchers using allozyme analysis have been able to confirm the continuous distribution of Zygaena exulans in between the foothills of the Pyrenees and the Alps during the last ice age. [16]

In eastern North America, lowland glacial refugia along the Atlantic and Gulf Coasts host endemic plants — some of which are rare, even endangered, and others entail the most southerly disjunct populations of plants that commonly appear only hundreds of miles to the north. Major rivers draining southward from the Appalachian Mountains are associated with a gradation of paleoendemic tree species. These range from the extinct Critchfield spruce near the outlet of the Mississippi River, to extinct-in-the-wild Franklinia along the Altamaha River, to the critically endangered Florida torreya and Florida yew at the downstream end of the Chattahoochee River system. [11] [17] (See illustration at right.)

See also

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<i>Zelkova</i> Genus of trees

Zelkova is a genus of six species of deciduous trees in the elm family Ulmaceae, native to southern Europe, and southwest and eastern Asia. They vary in size from shrubs to large trees up to 35 m (115 ft) tall. The bark is smooth, dark brown. Unlike the elms, the branchlets are never corky or winged. The leaves are alternate, with serrated margins, and a symmetrical base to the leaf blade. The leaves are in two distinct rows; they have pinnate venation and each vein extends to the leaf margin, where it terminates in a tooth. There are two stipules at each node, though these are caducous, leaving a pair of scars at the leaf base. Zelkova is polygamous. Staminate flowers are clustered in the lower leaf axils of young branchlets; the perianth is campanulate, with four to six lobes, and the stamens are short. Pistillate and hermaphrodite flowers are solitary, or rarely in clusters of two to four, in the upper leaf axils of young branchlets. The fruit is a dry, nut-like drupe with a dorsal keel, produced singly in the leaf axils. The perianth and stigma are persistent.

<span class="mw-page-title-main">Last Glacial Period</span> Period of major glaciations of the Northern Hemisphere (115,000–12,000 years ago)

The Last Glacial Period (LGP), also known as the Last glacial cycle, occurred from the end of the Last Interglacial to the beginning of the Holocene, c. 115,000 – c. 11,700 years ago, and thus corresponds to most of the timespan of the Late Pleistocene.

<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.

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<span class="mw-page-title-main">Last Glacial Maximum</span> Circa 24,000–16,000 BCE; most recent era when ice sheets were at their greatest extent

The Last Glacial Maximum (LGM), also referred to as the Last Glacial Coldest Period, was the most recent time during the Last Glacial Period where ice sheets were at their greatest extent between 26,000 and 20,000 years ago. Ice sheets covered much of Northern North America, Northern Europe, and Asia and profoundly affected Earth's climate by causing a major expansion of deserts, along with a large drop in sea levels.

<span class="mw-page-title-main">Cordilleran ice sheet</span> Major ice sheet that periodically covered large parts of North America during glacial periods

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<span class="mw-page-title-main">Glacial lake</span> Lake formed by a melted glacier

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

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<span class="mw-page-title-main">Mammoth steppe</span> Prehistoric biome

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<span class="mw-page-title-main">Oldest Dryas</span> Abrupt climatic cooling event during the last glacial retreat

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<span class="mw-page-title-main">Glacier morphology</span> Geomorphology of glaciers

Glacier morphology, or the form a glacier takes, is influenced by temperature, precipitation, topography, and other factors. The goal of glacial morphology is to gain a better understanding of glaciated landscapes and the way they are shaped. Types of glaciers can range from massive ice sheets, such as the Greenland ice sheet, to small cirque glaciers found perched on mountain tops. Glaciers can be grouped into two main categories:

<span class="mw-page-title-main">Last Glacial Maximum refugia</span> Places of survival during glaciation

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<span class="mw-page-title-main">Montane ecosystems</span> Ecosystems found in mountains

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

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According to the northern cryptic glacial refugial hypothesis, during the last ice age cold tolerant plant and animal species persisted in ice-free microrefugia north of the Alps in Europe. The alternative hypothesis of no persistence and postglacial immigration of plants and animals from southern refugia in Europe is sometimes also called the tabula rasa hypothesis.

<span class="mw-page-title-main">Penultimate Glacial Period</span> Glacial age that occurred before the Last Glacial Period

The Penultimate Glacial Period (PGP) is the glacial period that occurred before the Last Glacial Period. The penultimate glacial period is officially unnamed just like the Last Glacial Period. The PGP lasted from ~194,000 years ago, to ~135,000 years ago, and was succeeded by the Last Interglacial. The PGP also occurred during Marine Isotope Stage 6 (MIS6). At the glacial ages' height, it is known to be the most extensive expansion of glaciers in the last 400,000 years over Eurasia, and could be the second or third coolest glacial period over the last 1,000,000 years, as shown by ice cores. Due to this, the global sea level dropped to between 92 and 150 metres below modern-day global mean sea level. The penultimate glacial period expanded ice sheets and shifted temperature zones worldwide, which had a variety of effects on the world's environment, and the organisms that lived in it. At its height, the penultimate glacial period was a more severe glaciation than the Last Glacial Maximum. The PGP covers the last period of the Saalian glaciation in Europe, called the Wolstonian Stage in Britain, and is equivalent to the Illinoian in North America.

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A glacial relict is a population of a species that was common in the Northern Hemisphere prior to the onset of glaciation in the late Tertiary that was forced by climate change to retreat into refugia when continental ice sheets advanced. They are typically cold-adapted species with a distribution restricted to regions and microhabitats that allow them to survive despite climatic changes.

References

  1. ↑ Horsák, Michal; Limondin-Lozouet, Nicole; Juřičková, Lucie; Granai, Salomé; Horáčková, Jitka; Legentil, Claude; Ložek, Vojen (15 June 2019). "Holocene succession patterns of land snails across temperate Europe: East to west variation related to glacial refugia, climate and human impact". Palaeogeography, Palaeoclimatology, Palaeoecology . 524: 13–24. Bibcode:2019PPP...524...13H. doi:10.1016/j.palaeo.2019.03.028. S2CID   134640979 . Retrieved 14 November 2022.
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  17. ↑ Barlow, Connie. "Paleoecology and the Assisted Migration Debate: Why a Deep-Time Perspective Is Vital (Torreya taxifolia as exemplar)". Torreya Guardians. Retrieved 23 June 2022.
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