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Geographic Speciation in Tropical Echinoids

Ernst Mayr
Evolution
Vol. 8, No. 1 (Mar., 1954), pp. 1-18
DOI: 10.2307/2405661
Stable URL: http://www.jstor.org/stable/2405661
Page Count: 18
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Geographic Speciation in Tropical Echinoids
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Abstract

If the world distribution of the 16 genera of West Indian shallow water echinoids is mapped, it is found that each genus consists of one or several groups of allopatric species (see maps). The differences between many of these allopatric 'species' is sufficiently slight to indicate that some are better considered subspecies Allopatric populations show every grade of distinctness, ranging from mere statistical difference through subspecific to specific rank. Superspecies are frequent. This pattern of geographic variation is the same as that found in terrestrial animals with geographic speciation. Geographic speciation is also suggested by the distribution pattern of groups with a different ecology, such as deep sea organisms (crinoids) and pelagic organisms (scyphomedusae). The eastern Pacific, the Isthmus of Panama and the cold waters of southwest Africa appear to be the most important dispersal barriers and hence speciation agents for warm water echinoids. The presented data indicate that the prevailing speciation process in sexually reproducing marine animals is that of geographic speciation. No evidence was found which would require any other mode of speciation.

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