Relationship of Genetic Variation to Population Size in Wildlife

Genetic diversity is one of three levels of biological diversity requiring conservation. Genetic theory predicts that levels of genetic variation should increase with effective population size. Soulé (1976) compiled the first convincing evidence that levels of genetic variation in wildlife were related to population size, but this issue remains controversial. The hypothesis that genetic variation is related to population size leads to the following predictions: (1) genetic variation within species should be related to population size; (2) genetic variation within species should be related to island size; (3) genetic variation should be related to population size within taxonomic groups; (4) widespread species should have more genetic variation than restricted species; (5) genetic variation in animals should be negatively correlated with body size; (6) genetic variation should be negatively correlated with rate of chromosome evolution; (7) genetic variation across species should be related to population size; (8) vertebrates should have less genetic variation than invertebrates or plants; (9) island populations should have less genetic variation than mainland populations; and (10) endangered species should have less genetic variation than nonendangered species. Empirical observations support all these hypotheses. There can be no doubt that genetic variation is related to population size, as Soulé proposed. Small population size reduces the evolutionary potential of wildlife species.