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Several patterns in the phenotypic variation of island populations of the lizard Uta stansburiana are described: 1. The overall variation of a particular local population on an island is representative of the variation in any local population on that island. 2. There is strong evidence for a population variation parameter. That is, if a population is relatively variable for character A, it will be relatively variable for characters B, C, and so on. The implication is that some pervasive quality of a gene pool (or gene pool-environment interaction) determines the level of variation. It is argued that this quality is the average genic heterozygosity of the population. 3. Correlation and multiple regression analysis show that the log of island area is the best predictor of overall variation. Three hypotheses that might account for this correlation are tentatively rejected: (a) the tendency for gene flow among semi-isolated local populations to increase variation, (b) the accumulation of neutral alleles as a function of population size, and (c) genetic drift. A fourth is tentatively accepted: that overall variation (thought to reflect heterozygosity) is an equilibrium representing the benefits of heterosis offset by the loss of heterozygosity as a function of selection related to the relative novelty and simplicity of the environment. 4. Two other variables, possibly representing isolation and evolutionary divergence, also account for some of the diminution of variation in the island populations.
Michael Soulé (Sat,) studied this question.