The Relationship between Adrenal Weight and Population Status of Urban Norway Rats

Abstract

It has been proposed that changes in the size of animal populations exert density-dependent effects on the physiology of individuals in these populations (Christian, 1950). Theoretically, the magnitude of the physiological alterations would increase with increases in population size until there is a cessation of population growth followed by a decline or, in extreme cases, a population crash. Emphasis was placed on the adaptive reactions of the pituitary-adrenocortical and reproductive systems to density-dependent stimuli which were presumably sociopsychological in nature. Therefore these stimuli would be effective throughout the history of a population, changing only in magnitude with changes in population size. Environmental hardships, such as food shortages and disease, of necessity would be imposed on and additive to this basic response to density.