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An Estimate of the Potential Evolutionary Increase in Species Density in the Polynesian Ant Fauna

Edward O. Wilson and Robert W. Taylor
Evolution
Vol. 21, No. 1 (Mar., 1967), pp. 1-10
DOI: 10.2307/2406735
Stable URL: http://www.jstor.org/stable/2406735
Page Count: 10
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An Estimate of the Potential Evolutionary Increase in Species Density in the Polynesian Ant Fauna
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Abstract

1. Few if any ant species are native to Polynesia east of Rotuma, Samoa, and Tonga. The central and eastern archipelagoes have been populated in large part by 35 "tramp" species carried there from various parts of the tropics by human commerce. Several other tramp species are known to have been carried to the Pacific but are not yet established in the center and east. The tramp species also occur, along with native ones, in western Polynesia and outside the Pacific area. 2. No one island contains all of the tramp species, and most contain less than one-fourth of them. Several lines of evidence suggest that the species densities have stabilized. Competitive replacement has evidently played a role in the stabilization. 3. The species numbers are considered not to be resting at perfect equilibrium but rather to be at most at a "quasi-equilibrium." If the immigration rates of the 38 tramp species (35 established and 3 others available) were held constant, and after all the species had an opportunity to colonize a given island, the number at quasi-equilibrium could still be expected to increase slowly as local adaptation proceeded through evolution. 4. By comparing the newly assembled tramp faunulae with older native faunulae of Indo-Australian origin in Samoa, an estimate of the potential increase in species numbers through evolution was made. On an island with the size and history of Upolu the factor of increase should be between 1.5 and 2. 5. Estimates can then be made for islands of all areas if the slope of the changing species-area curve holds constant (Fig. 5).

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