Niche Breadth and Genetic Variability in Sympatric Natural Populations of Drosophilid Flies

Since a correlation between environmental heterogeneity and genetic variability has been widely hypothesized, 11 sympatric species of drosophilid flies were examined for allozyme variability and niche breadth based on microdistribution. Niche breadth and genetic variability were not correlated. Possible reasons for the lack of correlation may be that (1) the Colwell-Futuyma weighted niche metric fails to represent uniformly different species' responses to microdistribution; (2) parameters determining microdistribution are random or semirandom with respect to selective forces operating upon the loci; (3) species with similar niche breadths may have qualitatively differing genetic strategies, i.e., some respond to the environmental gradients as fine-grained while others react as coarse-grained with resultant selection against or for polymorphism independent of niche breadth; and (4) alleles may be largely selectively neutral. Although these considerations point toward no correlation, Powell (1971) found a relation between environmental heterogeneity and increased heterozygosity.