COMPETITION BETWEEN METAL TOLERANT AND NORMAL PLANT POPULATIONS; A FIELD EXPERIMENT ON NORMAL SOIL.

Abstract

In broad terms, the fitness of an individual may be considered as being a measure of its capacity to leave viable offspring. Ability to leave viable offspring will be influenced by genetic factors, environmental factors, and the interaction of these two. Amongst environmental factors of importance will be the effects of neighbors, which may be such as to enhance fitness, or to reduce it through competition for nutrients, light, water or space. In plants, genetically determined differences in competitive ability, have been shown almost exclusively in crops, oats and barley (de Wit, 1960), rice (Jennings and de Jesus, 1968), in barley and wheat (Adams and Allard, 1969), in soy beans (Schutz and Brim, 1967) and flax and linseed (Khan et al., 1974), whilst the benefits in terms of yield of herbage of the grass/ clover mixture in agriculture are widely documented (Davies, 1960; Cowling et al., 1964). The data of Harlan and Martini (1938) illustrate the influence of genotype environment interaction in changing the dominant type in competing mixtures of barley varieties. These genetically determined differences in competitive abilities must constitute a major factor in the relative fitness of individuals under many differing environmental conditions, and as such they have long been considered as playing a significant role in natural selection. The extensive studies of the evolution of heavy metal tolerance in plants (summarised by Antonovics et al., 1971) have