The experiments described in this paper are part of a continuing series on predator-prey interactions. The six-spotted mite, Eotetranychus sexmaculatus (Riley), was used for the study, which involved various ecosystems containing combinations of oranges and rubber balls, over which the mites moved in search of food. Effects of food dispersion on equilibrium level of a population, changes in its numbers, and its utilization of a limited resource were studied. Two main points are emphasized: First, food may be a limiting and regulating factor for a given population even if utilization of supply at equilibrium is low. Second, in some particular kinds of ecosystems, where competition for food is the regulating factor, superimposition of other mortality factors may alter the density level at which the competition is regulative, and thus result in levels of food utilization varying from low to high. Roles and importance of density-dependent and density-independent factors in the natural control of populations are also discussed.

A note on the definition and ecological implication of the term “competition” is included.