| Abstract: | A model is proposed in which niche choice precedes natural selection in an individual's life span; the panmictic population occupies an environment divided into niches, each contributing a constant proportion of parents to the next generation. Niche choice and fitness within the niche are controlled either by the same locus or by two linked loci. The conditions for a protected polymorphism are derived. It is shown that niche preferences can increase the protective effect of natural selection over a polymorphism. This effect depends on the existence of a positive correlation between preference for a niche and relative fitness within that niche, and also on the relative size of the niches. In the absence of within-niche fitness differences, alleles that cause preference for different niches can still be protected. Alleles that determine preference for niches contributing little to the total population can be eliminated by the ability to choose between niches. |
