Body Size of Free-Living Copepods

Abstract

Two genetically similar populations of Cyclops strenuus strenuus Fischer in two small ponds in southern Norway developed a considerable difference in body size under approximately the same temperature and other environmental conditions. The largest individuals were observed in the pond with the lowest population density. The relatively low densities observed and a supposed superabundance of food indicates that influence from crowding is doubtful. Laboratory experiments indicated that the differences in density in nature are too small to produce a significant size difference. Rate of development was not influenced by density differences in nature, but inversely related to density in the experiments. Fecundity showed a clear inverse relationship to density both in nature and in the laboratory experiments.