EXPERIMENTAL BACKGROUND TO THE STUDY OF THE DISTRIBUTION AND ABUNDANCE OF INSECTS: III. The relation between innate capacity for increase and survival of different species of beetles living together on the same food

When any one of the three beetles Rhizopertha dominica Fab., the small strain and the large of Calandra ory2ae L., was allowed to increase in numbers in a limited space in which the amount of food was kept constant, the maximum numbers which the populations attained were correlated with the innate capacity for increase (or the intrinsic rate of increase r) (Birch, 1953b). In this paper we shall examine whether there is a relationship between the numbers of these beetles and their innate capacity for increase when two species occur together in the one population. The experimental models which were set up are similar to those described in an earlier paper (Birch, 1953b) in which single species multiplied in amounts of grain which w7ere kept constant, except that in the present experiments each tube of grain contained two species; an adult male and female of each species were placed in each tube at the beginning. Combinations of temperature, moisture and food were chosen so that in some experiments one species had a higher innate capacity for increase than the other whilst in other experiments this same species had a lower innate capacity for increase than the other. The appropriate information for planning the experiments in this way was obtained from a previous paper (Birch, 195,3a). This latter aspect constitutes the novel feature of these experiments. Other workers have done experiments in which