Genetic Variation Within Plantago Populations

Abstract

Genetic variation is one of the means which enable a species to occupy an extensive geographic distribution and to occur in large numbers in heterogeneous environments. Genetic differentiation within a species can be manifested on different levels. Geographic races may occur in geographically different parts of the species range. In that case only a limited exchange of genes between remote parts of the distribution will occur. Genetic differences between populations can be brought about by chance processes, by selection and by a combination of both. If selection is the main cause for differentiation both geographical distance and genetic isolation will be relatively less important factors in structuring the genetic variation. In that case different specific genotypes (ecotypes) each adapted to specific environmental conditions, will occur. In many cases populations will consist of a single, particular, ecotype though also several ecotypes within a population may occur, depending on the level of hybridization and the habitat heterogeneity