Ecology of Populations

Publisher Website
Google Scholar
Abstract
The study of the correlation between the density of population and the environment represents the leading problem of the ecology of populations. Density of populations of Orthoptera was examined with respect to their relation to the temp., relative humidity, and evaporation in appropriate micro-habitats. Analyses of this material and of Shorygin''s data on the distribution of echinoderms of the Barents Sea can be expressed mathematically by means of the generalized curve of error. This enables one to take the mean value for the location of the ecological optimum of a sp.; then the standard deviation shows its ecological plasticity. The ecological plasticity of a sp. is shown to have a close connection to the location of the average environmental conditions with regard to ecological op-tima and extreme conditions. The experimental study of the influence of temp. on the density of saturating populations of Drosophila, Moina (data by Terao), and yeast (Saccharomyces cerevisiae) shows that temp. influences the density of the saturating population. Thus with yeast at 39[degree] the population reaches its asymptotic value at 1.94 cells per unit volume 28 hrs. after the beginning of the exp. and at 5.7[degree] a similar value of 2.55 is reached only after 28 days. In all these exps. on Moina and on yeast, the equilibrium attained was not due to food deficiency and the sharp decrease found in saturating populations of Drosophila adults (larvae and pupa remained uncounted) at 30[degree] as compared with 29[degree] was not due to lack of food. The influence of temp. on the density of the saturating population of Moina in relation to temp. is tentatively expressed by the generalized curve of error; that of the yeast population, by the aid of Pearson''s first type of curve. The conclusion is reached that "it remains for future investigations to discover, by an analysis of the population growth of various organisms, to what causes this type of connection is due.".