Cycles
Last Review/Updated: May 31, 2002
Several species of northern mammals go through periodic cycles of population change. Over a period of time, a population will steadily rise in numbers, suddenly "crash" to very low numbers, only to rise again. Of the lagomorphs and large rodents, the snowshoe hare and muskrat tend to cycle about once every ten years.
The snowshoe hare cycle is one of the best known. At the "peak" of the cycle, population densities as high as 4000 hares per square kilometre (10 000/sq. mi.) have been estimated. Within a period of one year, these populations can crash to densities of less than one hare per square kilometre (2.6/sq. mi.). Over the next 6 to 13 years, the populations slowly return to their peak densities. As the hares increase in numbers, they reduce their food supply, and individuals eat less desirable and less nutritious vegetation. Because hares are plentiful and easy to find, more predators feed on them. Eventually one of several diseases, a chief cause of population crashes, kills all but the most hardy individuals.
Because the snowshoe hare is the principal prey of lynx, lynx populations also cycle about once every ten years.
