Studies on Natural Populations Ofdrosophilavi. Competition Betweendrosophila Melanogasteranddrosophila Simulans

The dynamics of natural populations of Drosophila have been investigated by a large number of biologists who have focused their attention upon the “competition” problem, where they have investigated the competitive relationship within and between the closely related species. Recently, Kohn and Orians (1962) stated that competition between species reveals ecological differences “permitting coexistence of stable populations of closely related species of various kinds of animals.” For a review, references given by Barker (1963), Miller ( 1964a, b) , and Narise (1965) should be consulted. Natural selection often operates through competition which allows various forms to survive and establish themselves under certain environmental conditions. I t tends to eliminate, gradually or rapidly, other forms living under the same conditions. The special interest of sibling species of Drosophila stems from their morphological and ecological similarities as well as their known close genetical relationships (Tantawy, 1964). The present experiments were designed to study larval and adult competition within and between populations of Drosophila melanogaster and Drosophila simulans a t two different temperatures, 15 and 2 5 C, and to see to what extent separately measured components of competitive ability could predict the outcome of competition.