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Trends in the Insular Radiation of a Lizard

Michael Soule
The American Naturalist
Vol. 100, No. 910 (Jan. - Feb., 1966), pp. 47-64
Stable URL: http://www.jstor.org/stable/2459378
Page Count: 18
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Trends in the Insular Radiation of a Lizard
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Abstract

1) An estimate of body size in Uta populations on nine deep-water islands in the Gulf of California is found to be inversely proportional to the square root of the number of sympatric species of iguanid lizards. It is tentatively concluded that (a) small size of Uta on the continent and on large islands is largely affected by interspecific interactions with other iguanid lizards; (b) the intensity of this inhibition to evolutionary increase in size is dependent (but not linearly) on the number of iguanid species interacting with Uta. Other supporting evidence for the existence of interspecific phenomena affecting the ecology and distribution of lizards is presented. 2) The relative size of scales on the dorsal surface of the body is found to be significantly correlated with the area of the island. This and other data on the geographic variation of scales of North American reptiles support the hypothesis that scales are thermoregulatory structures important in heat exchange with the environment, and that scale size and form is partly determined by the selective effects of climate. 3) The extremely high densities of some insular populations of Uta is interpreted as an evolutionary response to new food sources, assuming, of course, an hereditary component in the behavioral mechanisms that determine territory size. In continental areas, gene flow impedes adaptation to such local peculiarities in the availability of food. 4) The existence of the above patterns in the geographic variation of body size, scale size, and population density testifies to the importance of environmental selective trends in the evolutionary control of these insular lizard populations.

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