<p>This article develops stochastic models of different ecological mechanisms of natural selection that explicitly account for the interdependence of individual fates in case of ecological competition. Competition as a zero-sum game makes the fates of individuals interdependent. Competition for a limited resource and competition to escape predators are shown to have markedly different statistical properties. The effect of selection depends not only on individual phenotypes, but also on the strength of competition. This is illustrated with simulations comparing five different selection mechanisms with and without competition. It is shown how the rate of genetic change, the probability of fixation of a mutant allele, mean fixation time, etc. depend on the strength of competition, fitness ratio between individuals with different competitive abilities, initial allele fraction, population size, and Mendelian dominance. The effect of competition is reduced when mobility is limited so that individuals can compete with conspecifics only within a limited distance. This is regarded as imperfect interdependence. A lower limit for the effect of competition under imperfect interdependence is estimated. The statistical effects of different forms of ecological competition is a previously neglected area of study where many traditional models ignore the interdependence of fates.</p>