The problem of population variation and its relationship to ecological variability is one of continuing interest to ecologists. The problem is here addressed with experiments on the early successional annual, Amaranthus retroflexus. The germination responses of homozygous genotypes were compared over a range of oxygen concentrations. These genotypes were also compared with respect to their distributions along a soil moisture gradient. The germination behavior of the two PGI genotypes in response to oxygen availability was found to differ substantially, particularly at the lower oxygen concentrations. Homozygous fast (FF) genotypes were inhibited less by low oxygen availability relative to the homozygous slow (SS) genotypes. Similarly the performance of the two genotypes in mixture along the soil moisture gradient differed such that homozygous fast (FF) genotypes performed best at high soil moistures, while the homozygous slow (SS) genotypes performed best at moderate soil moistures. A field survey revealed that both alleles frequently co—occur in natural populations. Heterozygous individuals are, however, rare in both field and glasshouse populations, indicating a high level of inbreeding in the species. Inbreeding will tend to maintain the distinctiveness of genotypes within Amaranthus populations, perhaps leading to the large between—genotype component of niche breadth that was observed on the soil moisture gradient.

Zangerl, A. R., & Bazzaz, F. A. (1984). Niche Partitioning Between Two Phosphoglucoisomerase Genotypes in Amaranthus Retroflexus. Ecology, 65(1), 218–222. Portico.