Populations of Ciliates

Abstract

A FEW years ago Jahn (1934), in a discussion of problems of population growth in the protozoa, stated that a mathematical analysis of most of the data concerning growth of protozoan populations would not appreciably increase our understanding of the matter because, in most of the investigations in this field, the various factors which might affect the results were not adequately controlled. The situation is much the same to-day. We are still in the process of acquiring information about the factors which operate in such populations and of obtaining control over these factors. But there has been progress. A survey of the investigations of ciliate populations made during the past thirty years reveals progress in the techniques employed. In the beginning, such studies were made using unknown mixed bacteria as the source of food; then known bacteria were used; then known bacteria in definite amounts suspended in a non-nutritive reproducible salt solution were used; and, finally pure culture, in which no other form of life was present other than the one species being studied, was attained. Most of the pure culture studies up to the present time have been made on a few species, but recent developments, which will be referred to later, point to an extension of the pure culture technique in the future. In such population studies what are some of the questions for which answers are being sought? In general the fundamental problems for analysis in studies of ciliates are the same as those found in similar studies of other kinds of organisms. The question of what factors affect the rate of population growth and the question of what factors limit population increase have been the primary concern of most workers on ciliate populations. The question of what goes on in a stabilized population,