Relations between Climate and Intraspecific Variation in Plants

Abstract

Species are defined as groups whose members can interbreed and produce subsequent generations of offspring as vigorous and fertile as the original parents. Included in the definition are individuals which, though mutually intersterile, may be linked together genetically through an intermediary. The ability of a species to occupy > 1 climatic zone obviously depends upon its racial diversity. Spp. of wide distribution generally consist of several climatic races, or ecotypes, as demonstrated by Turesson and confirmed by the writers. Ecotypes are generally best fitted to survive in habitats like those in which they occur naturally. Climatic races, however, are not homogenous. Examples of variation within coastal populations of Achillea borealis are presented. The most extreme maritime populations consist of short individuals, but populations only 1 mi. from the sea are twice as tall. At intermediate locations a mixture of individuals was found, some of which corresponded to those from the immediate coast, others to those 1 mi. from the coast. Such mixed populations would offer material for natural selection. When different climatic races are crossed, many new combinations of characters are found in the Fa. In Potentilla glandulosa the reactions of an F2 population of a cross between an alpine and a Sierran foothill race were compared at an alpine, a mid-Sierran and a coastal station in California. Clone members of each individual were grown at all 3 stations. Marked individual differences in survival capacities are observed. This variation transgresses the limits of the parental types. Thus new climatic laces may be synthesized by crossing and selection. The significance of such exptl. evidence for a conception of plant-climate interrelationships is discussed.