A population cycle in zoology is a phenomenon where

population Population typically refers to the number of people in a single area, whether it be a city or town, region, country, continent, or the world. Governments typically quantify the size of the resident population within their jurisdiction using ...

s rise and fall over a predictable period of time. There are some species where population numbers have reasonably predictable patterns of change although the full reasons for population cycles is one of the major unsolved ecological problems. There are a number of factors which influence population change such as availability of food, predators, diseases and climate.

Occurrence in mammal populations

Olaus Magnus Olaus Magnus (October 1490 – 1 August 1557) was a Swedish writer, cartographer, and Catholic ecclesiastic. Biography Olaus Magnus (a Latin translation of his birth name Olof Månsson) was born in Linköping in October 1490. Like his elder b ...

, the Archbishop of

Uppsala Uppsala (, or all ending in , ; archaically spelled ''Upsala'') is the county seat of Uppsala County and the List of urban areas in Sweden by population, fourth-largest city in Sweden, after Stockholm, Gothenburg, and Malmö. It had 177,074 inha ...

in central Sweden, identified that species of northern

rodent Rodents (from Latin , 'to gnaw') are mammals of the Order (biology), order Rodentia (), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are roden ...

s had periodic peaks in population and published two reports on the subject in the middle of the 16th century. In North America, the phenomenon was identified in populations of the

snowshoe hare The snowshoe hare (''Lepus americanus''), also called the varying hare or snowshoe rabbit, is a species of hare found in North America. It has the name "snowshoe" because of the large size of its hind feet. The animal's feet prevent it from sin ...

. In 1865, trappers with the

Hudson's Bay Company The Hudson's Bay Company (HBC; french: Compagnie de la Baie d'Hudson) is a Canadian retail business group. A fur trade, fur trading business for much of its existence, HBC now owns and operates retail stores in Canada. The company's namesake b ...

were catching plenty of animals. By 1870, they were catching very few. It was finally identified that the cycle of high and low catches ran over approximately a ten-year period. The most well known example of creatures which have a population cycle is the

lemming A lemming is a small rodent, usually found in or near the Arctic in tundra biomes. Lemmings form the subfamily Arvicolinae (also known as Microtinae) together with voles and muskrats, which form part of the superfamily Muroidea, which also incl ...

.The Lemming Cycle
Nils Christian Stenseth, University of Oslo The biologist

Charles Sutherland Elton Charles Sutherland Elton (29 March 1900 – 1 May 1991) was an English zoologist and animal ecologist. He is associated with the development of population and community ecology, including studies of invasive organisms. Personal life Charle ...

first identified in 1924 that the lemming had regular cycles of population growth and decline. When their population outgrows the resources of their habitat, lemmings migrate, although contrary to popular myth, they do not jump into the sea. Mouse plagues in Australia happen at intervals of about four years.

Other species

While the phenomenon is often associated with rodents, it does occur in other species such as the

ruffed grouse The ruffed grouse (''Bonasa umbellus'') is a medium-sized grouse occurring in forests from the Appalachian Mountains across Canada to Alaska. It is the most widely distributed game bird in North America. It is non-migratory. It is the only specie ...

. There are other species which have irregular population explosions such as

grasshoppers Grasshoppers are a group of insects belonging to the suborder Caelifera. They are among what is possibly the most ancient living group of chewing herbivorous insects, dating back to the early Triassic around 250 million years ago. Grasshop ...

where overpopulation results in

locust Locusts (derived from the Vulgar Latin ''locusta'', meaning grasshopper) are various species of short-horned grasshoppers in the family Acrididae that have a swarming phase. These insects are usually solitary, but under certain circumst ...

swarms in Africa and Australia.

Relationships between predators and prey

There is also an interaction between prey with periodic cycles and predators. As the population expands, there is more food available for predators. As it contracts, there is less food available for predators, putting pressure on their population numbers.

Length

Each population cycle tends to last as long as a species' life expectancy (i.e. lemmings,

rabbits Rabbits, also known as bunnies or bunny rabbits, are small mammals in the family Leporidae (which also contains the hares) of the order Lagomorpha (which also contains the pikas). ''Oryctolagus cuniculus'' includes the European rabbit spe ...

and

locusts Locusts (derived from the Vulgar Latin ''locusta'', meaning grasshopper) are various species of short-horned grasshoppers in the family Acrididae that have a swarming phase. These insects are usually solitary, but under certain circumst ...

)

References

Online references

''Hutchinson Encyclopaedia'' article

* ttp://www.sysecol.ethz.ch/pdfs/Ba061.pdf Paper by Baltensweiler, W. & Fischlin, A., 1988. The larch bud moth in the Alps

Other references

* ''Encyclopædia Britannica Online'' 25 August 2005 "Population Ecology" article section on Population Cycles *Errki Korpimaki and Charles J Krebs "Predation and Population Cycles of Small Mammals" ''Bioscience'' November 1996 Volume 46, Number 10