A Study of the Changes in an Aquatic Insect. Population, using Minnows as Predators

Collections of three species of Corixids were made at regular intervals from a small pond at Wilpshire, near Blackburn, Lancashire. After fifty Minnows had been introduced the proportions of Corixids adapted to the habitat increased. Various possible explanations are considered, and it seems most probable that the Minnows destroyed those insects which did not harmonize with the background. There is a lower intensity of selection under natural conditions than that observed in the laboratory. The influence of selection and isolation in the spread and preservation of various types of characters is also discussed.