Abstract
Since Elton’s account and description of population cycles in 1924, a vast amount of research has been undertaken to ascertain what animals have three to four ye a r cyclic fluctuations and what mechanisms are responsible for these seemingly predictable changes. For many years the spectacular increase and decrease (crash) of certain arctic mammals has stimulated such research on sundry populations. Researchers at first sought a n explanation for the "crash”, however, most investigators now seek a description and understanding of the interaction and relative importance of the many factors that influence the increases and decreases of populations. Precise accounts of fluctuations in several gallinaceous birds and a high percentage of the mammals are, to date, well documented. However, the controlling mechanisms involved in these cyclic fluctuations have not (in the face of incomplete and often contradictory information) been elucidated. One must bear in mind that cyclic fluctuations of animals are acting concurrently and in addition to seasonal or annual changes in numbers.