ESTIMATES OF FITNESS IN ERODWM POPULATIONS WITH INTRA- AND INTERSPECIFIC COMPETITION.

Abstract

One factor affecting the fitness of a genotype in a population is competition. Competition and competitive ability have been defined in many ways. This study is concerned with genetic variation in competitive ability in annual plants. The definition of competitive ability used in this study is the ratio of seed production (fecundity) of a genotype in competition with other individuals to the seed production (fecundity) of a genotype when grown alone at a comparable density. Many studies have examined genetic variation in interspecific competition (e.g., Lerner and Ho, 1961 in Tribolium; Ayala, 1969, 1970 in Drosophila; Solbrig and Simpson, 1974, 1977 in dandelions). Variation in intraspecific competition has been found in Linum (Khan et al., 1975), soybeans (Schutz and Brim, 1967) and barley (Allard and Adams, 1969). Further studies are needed on this topic. How is the fitness of a genotype in competition related to the fitness of that genotype growing without competition? What is the relationship between intraspecific and interspecific competitive abilities of a genotype? Differences in interspecific competitive performance among mixed cultures of Erodium cicutarium and E. obtusiplicatum have been found (Martin and Harding, 1981). In a mixed culture of populations of E. cicutarium and E. obtusiplicatum that are sympatric in nature, each of the two populations was favored at lower frequencies, leading to the prediction of a stable equilibrium. In mixed cultures of E. cicutarium and E. obtusipli-