Environmental Fluctuations and Population Size

Abstract

BOROWSKY has analysed the magnitude and pattern of the temporal fluctuations of experimental populations of Drosophila¹, and has shown that the fluctuations are not randomly distributed in their direction; the frequencies of the competing species change in the same direction (upwards or downwards) more frequently than would be expected by chance alone. Moreover, he has demonstrated that the fluctuations are larger in amplitude than is expected in a binomial distribution. He concludes correctly that some external factor or factors are responsible for the magnitude and non-random association of the fluctuations, on which the most important environmental influence is probably temperature. I believe, however, that other uncontrolled variations in the quality and quantity of food, humidity, and so on, may have contributed as much as, or more than, temperature to the pattern and amplitude of the fluctuations of the experimental populations.