Nunatak hypothesis
Encyclopedia
In biogeography, particularly phytogeography
, the nunatak hypothesis about the origin of a biota in formerly glaciated areas refers to the idea that some or many species have survived the inhospitable period on icefree land such as nunatak
s. Its antithesis is the tabula rasa hypothesis, which posits that all species have immigrated into completely denuded land after the retreat of glaciers.
By the mid-20th Century, the nunatak hypothesis was widely accepted among biologists working on the floras of Greenland
and Scandinavia
. However, while modern geology has established the presence of icefree areas during the last glacial maximum in both Greenland
and Scandinavia
, molecular techniques have revealed limited between-region genetic differentiation in many Arctic
taxa
, strongly suggesting a general capacity for long-distance dispersal among polar organisms. This does not directly disprove glacial survival. But it makes it less necessary as an explanation. Moreover, populations that survived on icefree land have probably in most cases been genetically flooded by postglacial immigrants.
Phytogeography
Phytogeography , also called geobotany, is the branch of biogeography that is concerned with the geographic distribution of plant species...
, the nunatak hypothesis about the origin of a biota in formerly glaciated areas refers to the idea that some or many species have survived the inhospitable period on icefree land such as nunatak
Nunatak
A nunatak is an exposed, often rocky element of a ridge, mountain, or peak not covered with ice or snow within an ice field or glacier. The term is typically used in areas where a permanent ice sheet is present...
s. Its antithesis is the tabula rasa hypothesis, which posits that all species have immigrated into completely denuded land after the retreat of glaciers.
By the mid-20th Century, the nunatak hypothesis was widely accepted among biologists working on the floras of Greenland
Greenland
Greenland is an autonomous country within the Kingdom of Denmark, located between the Arctic and Atlantic Oceans, east of the Canadian Arctic Archipelago. Though physiographically a part of the continent of North America, Greenland has been politically and culturally associated with Europe for...
and Scandinavia
Scandinavia
Scandinavia is a cultural, historical and ethno-linguistic region in northern Europe that includes the three kingdoms of Denmark, Norway and Sweden, characterized by their common ethno-cultural heritage and language. Modern Norway and Sweden proper are situated on the Scandinavian Peninsula,...
. However, while modern geology has established the presence of icefree areas during the last glacial maximum in both Greenland
Greenland
Greenland is an autonomous country within the Kingdom of Denmark, located between the Arctic and Atlantic Oceans, east of the Canadian Arctic Archipelago. Though physiographically a part of the continent of North America, Greenland has been politically and culturally associated with Europe for...
and Scandinavia
Scandinavia
Scandinavia is a cultural, historical and ethno-linguistic region in northern Europe that includes the three kingdoms of Denmark, Norway and Sweden, characterized by their common ethno-cultural heritage and language. Modern Norway and Sweden proper are situated on the Scandinavian Peninsula,...
, molecular techniques have revealed limited between-region genetic differentiation in many Arctic
Arctic
The Arctic is a region located at the northern-most part of the Earth. The Arctic consists of the Arctic Ocean and parts of Canada, Russia, Greenland, the United States, Norway, Sweden, Finland, and Iceland. The Arctic region consists of a vast, ice-covered ocean, surrounded by treeless permafrost...
taxa
Taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...
, strongly suggesting a general capacity for long-distance dispersal among polar organisms. This does not directly disprove glacial survival. But it makes it less necessary as an explanation. Moreover, populations that survived on icefree land have probably in most cases been genetically flooded by postglacial immigrants.