Dynamics of Populations. I. Factors Controlling Population Growth and Population Size in Drosophila serrata

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Abstract
Eight populations of D. serrata were used in a factorial design to study the effect of some environmental and genetic factors on the productivity and total size of a population. The variables studied were 2 temperatures (25 versus 19[degree]C), 2 feeding schedules (2 versus 3 food units per week), and 2 genetic compositions (1 strain versus 2 strain hybrid population). The parameters measured were the number of flies and the biomass produced per food unit, and the total population size. The amount of food is the main factor controlling the number of flies and the biomass produced by a population. The main factor controlling the size of the population is, however, the living space. The hybrid populations are considerably superior to the single strain populations, both in productivity and in total size, presumably owing to the greater genetic variability they offer to the action of natural selection.