Adaptation, variation and selection in marginal areas

Summary

The word adaptation and its derivatives are reviewed as well as the characteristics of environmental marginality. Plant traits are discussed in the light of their adaptive significance, specially pointing at their phenotypic expression under stress. Variation in marginal plant populations is discussed on the basis of accumulated knowledge on quantitative traits and isozymes. The common opinion that marginal populations are genetically depauperated is questioned on the basis of observations that show high degrees of environmental heterogeneity. This in turn would cause a disruptive mode of natural selection close to the species margin. Species’ modes of adaptation and mating systems are briefly discussed and finally natural selection for stability is suggested to be of significance in marginal areas, a fact that should be duly recognized in modern plant breeding programmes aiming at maximum stability (sustainability) but not necessarily maximum yield.