Oceanic Dispersal Essay

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The resurrection of oceanic dispersal in historical biodiversity. by Alan de Queiroz.

The distribution of many taxa that are separated by oceans can be explained by either vicariance or oceanic dispersal. At first oceanic dispersal was the explanation used for the distribution of taxa separated by oceans. Since the 1930s till the 1960s time oceanic dispersal was the most common explanation because there were many plausible dispersal mechanisms that would make oceanic dispersal possible. Support for the plausibility of oceanic dispersal was provided by experiments performed by Darwin and his supporters that showed that organisms (mostly plants seeds) could survive in oceans for extensive time periods. More importantly it was argued that organisms
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Geographical distribution of where fossils were found also casts doubt on tectonic vicariance.

Tectonic vicariance relies on the overlap between area cladograms and fragmentation history. The discrepancy between these two factors does however, not imply that oceanic dispersal is the answer, because there are many different methods of dispersal.

Many studies have tried to prove the disjunct distribution of taxa to be due to vicariance alone, but sister taxa separated by an ocean can be explained by an old vicariance event or recent oceanic dispersal, but in most of these cases the molecular divergence is too small to be explained by vicariance. Studies using fossils showed that most plant species in New Zealand is due to oceanic dispersal. The size of the role oceanic dispersal plays in the distribution of animals is debateable. Some studies show that oceanic dispersal plays a small role in the distribution of Southern Hemisphere animals, since animals have more difficulty crossing oceanic barriers. Other studies, however, suggest that most vertebrate species from the West Indies and Madagascar are derived from ancestors that used oceanic dispersal. Oceanic dispersal is not necessarily more important than vicariance, but oceanic dispersal has a large role in these disjunct
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