- Population cycle
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 Mammal Populations
Olaus Magnus , the Archbishop ofUppsala in central Sweden, identified that species of northernrodent 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. 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 . The biologist 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 don't jump into the sea.Other Species
While the phenomenon is often associated with rodents, it does occur in other species such as the ruffed grouse. There are other species which have irregular population explosions such as grasshoppers where overpopulation results in
locust 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.
References
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]
* [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]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
ee also
*
Population dynamics
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