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[[File:Predator prey curve.png|500px|thumb]]
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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.
 
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[[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 [[Snowshoe Hare|snowshoe hare]].<ref>K. G. Poole. (1994). Characteristics of an Unharvested Lynx Population during a Snowshoe Hare Decline The Journal of Wildlife Management, 58(4), 608-618 [https://www.jstor.org/stable/3809673?seq=1]</ref><ref>[http://www.nps.gov/akso/ParkWise/Students/ReferenceLibrary/DENA/GoldenEagles/SnowshoeHareCycles.pdf Snowshoe Hare Cycles], National Park Service</ref> In 1865, trappers with the [[Hudson's Bay Company]] 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]].<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 Elton|Charles Elton]] 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==
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==Relationships between predators and prey==
{{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===
* [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 popuationpopulation cycles]
* [http://www.nps.gov/akso/ParkWise/Students/ReferenceLibrary/DENA/GoldenEagles/SnowshoeHareCycles.pdf National Parks Service Document on population cycles]
* [http://www.cas.uio.no/Publications/Jubilee/The_lemming_cycle.pdf Paper by Professor Stenseth, University of Oslo on lemming cycles]
* [http://www.sysecol.ethz.ch/pdfs/Ba061.pdf Paper by Baltensweiler, W. & Fischlin, A., 1988. The larch bud moth in the Alps]
 
===Software===
[http://www.futureskill.com Creatures!] High School interactive simulation program that implements an agent based simulation of grass, rabbits and foxes.
 
===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
 
===Further reading===
 
* Alan Berryman, ''Population Cycles'', Oxford University Press US, 2002 {{ISBN |0-19-514098-2}}
 
▲==See also==
▲* [[Population dynamics]]
 
{{modelling ecosystems|expanded=other}}
 
[[Category:Population]]
 
[[eo:Populaciciklo]]
Retrieved from "https://en.wikipedia.org/wiki/Population_cycle"