THE CONTROL OF POPULATION-DENSITY THROUGH SOCIAL BEHAVIOUR: A HYPOTHESIS

Any given species of animal generally occurs at a higher population-density where food is more plentiful, and vice versa ; quantitative evidence points to a rather close correlation between the two. Such density differences arise from the activities of the animals themselves, and this implies that population-density is subject to effective internal control, i.e., it is self-regulating.
A theory is put forward that, for each species, population-densities are limited at a safe level, which will protect the food-supply from long-term depletion and assure its renewal for the future. Instead of competing directly for food, animals compete for conventional substitutes, e.g. territory or social position, which are capable of imposing a ceiling density at the optimum level, and can prevent it from rising to the starvation level which would endanger future resources.
Such limitation by conventional means requires the existence of a social organisation. Forms of social competition supplant direct competition for food; their intensity is density-dependent and provides the animals with an index of population-density. This index serves as the "feed-back" for the machinery of density-adjustment, which operates, very broadly, through (1) direct movement (emigration/immigration), and (2) varying the birth and survival rates.