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]
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
In studies exploring the extent of glacial refugia in mountain species, three distinct types of glacial refugium have been identified.[3]
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.[13] 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.[13]
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.[14]
Lowland
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.[15]
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][16] (See illustration at right.)
^
abcdeHolderegger, R., Thiel-Egenter, C. (2009): A discussion of different types of glacial refugia used in mountain biogeography and phytogeography. Journal of Biogeography 36, 476-480.
^Klicka, John; Zink, Robert M. (1997-09-12). "The Importance of Recent Ice Ages in Speciation: A Failed Paradigm". Science. 277 (5332): 1666–1669.
doi:
10.1126/science.277.5332.1666.
ISSN0036-8075.
^Colinvaux, P. A.; De Oliveira, P. E.; Bush, M. B. (2000-01-01). "Amazonian and neotropical plant communities on glacial time-scales: The failure of the aridity and refuge hypotheses". Quaternary Science Reviews. 19 (1–5): 141–169.
Bibcode:
2000QSRv...19..141C.
doi:
10.1016/S0277-3791(99)00059-1.
^
abDelcourt, Hazel R; Delcourt, Paul A (October 1975). "The Blufflands: Pleistocene Pathways into the Tunica Hills". American Midland Naturalist. 94 (2): 385–400.
doi:
10.2307/2424434.
JSTOR2424434.
^Munaut, André-V. (May 1986). "An Atlas of past and present pollen maps of Europe: 0–13,000 years ago". Review of Palaeobotany and Palynology. 47 (3–4): 411–412.
doi:
10.1016/0034-6667(86)90044-8.
ISSN0034-6667.
^
abStehlik, Ivana (2000-06-01). Nunataks and peripheral refugia for alpine plants during quaternary glaciation in the middle part of the Alps. Birkhäuser.
OCLC753524599.
^Schönswetter, P.; Tribsch, A.; Barfuss, M.; Niklfeld, H. (December 2002). "Several Pleistocene refugia detected in the high alpine plant Phyteuma globulariifolium Sternb. & Hoppe (Campanulaceae) in the European Alps". Molecular Ecology. 11 (12): 2637–2647.
doi:
10.1046/j.1365-294x.2002.01651.x.
ISSN0962-1083.
PMID12453246.
S2CID14302480.
^Schmitt, Thomas; Hewitt, Godfrey M. (2004-05-07). "Molecular biogeography of the arctic-alpine disjunct burnet moth species Zygaena exulans (Zygaenidae, Lepidoptera) in the Pyrenees and Alps". Journal of Biogeography. 31 (6): 885–893.
doi:
10.1111/j.1365-2699.2004.01079.x.
ISSN0305-0270.
S2CID86301042.