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A '''population cycle''' in zoology is a phenomenon where [[population]]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
[[Olaus Magnus]], the Archbishop of [[Uppsala]] in central Sweden, identified that species of northern [[rodent]]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 [[
The most well known example of creatures which have a population cycle is the [[lemming]].<ref>[https://web.archive.org/web/20051223233155/http://www.cas.uio.no/Publications/Jubilee/The_lemming_cycle.pdf The Lemming Cycle] Nils Christian Stenseth, University of Oslo</ref> The biologist [[Charles Sutherland
[[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|ruffed grouse]]. There are other species which have irregular population explosions such as [[Caelifera|grasshoppers]] where overpopulation results in [[locust]] swarms in Africa and Australia.
==Relationships between
{{main|Lotka–Volterra equations}}
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]] and [[locusts]])
==Among humans==
{{See also|Societal collapse|Malthusianism}}
There is strong evidence that humans also display population cycles. Societies as diverse as those of England and France during the Roman, medieval, and early modern eras, of Egypt during Greco-Roman and Ottoman rule, and of various dynasties in China all showed similar patterns of political instability and violence becoming considerably more common after times of relative peace, prosperity, and sustained population growth. Quantitatively, periods of unrest included many times more events of instability per decade and occurred when the population was declining, rather than increasing.<ref>{{cite web | url=http://home.vicnet.net.au/~ozideas/poprus.htm | archive-url=https://web.archive.org/web/20110405081151/http://home.vicnet.net.au/~ozideas/poprus.htm | archive-date=2011-04-05 | title=Population crises and cycles in history - OzIdeas }}</ref>
[[File:Wars-Long-Run-military-civilian-fatalities.png|thumb|600x600px|Military and civilian fatalities|center]]
==See also==▼
* [[Population dynamics]]▼
==References==
{{reflist}}
===Online References===▼
* [http://www.tiscali.co.uk/reference/encyclopaedia/hutchinson/m0008093.html ''Hutchinson Encyclopaedia'' article]▼
* [http://www.extension.umn.edu/distribution/youthdevelopment/components/6340-02.html University of Minnesota Extension Service article on wildlife populations containing a section on population cycles]▼
▲* [https://archive.today/20130505105948/http://www.tiscali.co.uk/reference/encyclopaedia/hutchinson/m0008093.html ''Hutchinson Encyclopaedia'' article]
▲* [https://web.archive.org/web/20070310222535/http://www.extension.umn.edu/distribution/youthdevelopment/components/6340-02.html University of Minnesota Extension Service article on wildlife populations containing a section on population cycles]
* [http://www.sysecol.ethz.ch/pdfs/Ba061.pdf Paper by Baltensweiler, W. & Fischlin, A., 1988. The larch bud moth in the Alps]
===
* ''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
===Further reading===
* Alan Berryman, ''Population Cycles'', Oxford University Press US, 2002 {{ISBN
▲==See also==
▲* [[Population dynamics]]
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