The Beringia landbridge and continental species migration

Landbridges

Defining a landbridge is a matter of understanding how land masses are formed and where they can be found. A landbridge is a tract of land that is sometimes submerged by the ocean, and sometimes it's not. As this is a fluid situation, the tract of land at times is large enough to accommodate migration between the two larger bodies of land between which it is located, and sometimes it is so small as to be non-existent. The fluidity involved is based upon ocean waves and the depth of the ocean as it ebbs and flows. Because the ebbs and flows of the ocean change so slowly, the resulting landbridge usually changes just as slowly.

There are a number of notable landbridges including the Beringia Straits that in centuries gone by connected North America and Asia. The Sinai Peninsula connected Asia and Europe, and the Isthmus of Panama connects North America and South America.

Description

A landbridge can best be described as the exposed portions of the ocean bottom. A landbridge occurs because the ocean water that normally covers it has receded which leaves the land exposed that was not exposed before. A landbridge allows the migration of humans, plants and animals from one continent to another. As one recent study states "climatic and geological changes across time are presumed to have shaped the rich biodiversity of tropical regions" (Smith, Amei, Klicka, 2012, p. 3520). It is speculated that this rich biodiversity is due to the fact that migration could (and can) takes place via the Isthmus of Panama.

This holds true for the continents connected by other landbridges as well. Plants and animals found in one continent can easily be traced back to a connected continent and vice versa. The strongest premise can be said that the animals, plants and wildlife migrated between the two continents and in order for that to happen there had to be a connecting landbridge.

Another study determine that "results are in accordance with a recent leading edge mode of colonization, particularly towards the east throughout Canada/Greenland and across the North Atlantic into Scandinavia and Svalbard" (Bronken Eidesen, Carlsen, Molau, Brochmann, 2007, p. 1559). The same study concluded that C. tetragona expanded eastwards from Beringia several times and that the earlier emigrants of this woody species became extinct" (p. 1560).

Stability/Instability

The size and shape of a landbridge is due primarily to the ebbs and flows of the ocean. When talking about stability, however, the stability of the landbridge is usually pretty long-term due to the very slow nature of ocean recession or accession. The landbridge cannot really be classified as unstable. For example the Isthmus of Panama has been around for centuries, although that has not always been the case.