Polymorphism in Patchy Environments

A model of natural selection in a P-ploid organism living in a temporally and spatially varying environment is described. The spatial patchiness of the environment is measured in two ways, by the effective number of patches and by the correlation between patches. Increasing the effective number of patches, or decreasing the spatial correlation, makes genetic polymorphism more likely. The role of ploidy is analogous to the role of environmental patchiness in that it tends to lower the variance in the per generation change in allele frequency and thus increases the likelihood of polymorphism.