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Population density (in agriculture: standing stock and standing crop) is a measurement of population per unit area or unit volume; it is a quantity of type number density. It is frequently applied to living organisms, and particularly to humans. It is a key geographic term.〔Matt Rosenberg (Population Density ). Geography.about.com. March 2, 2011. Retrieved on December 10, 2011.〕 ''Lists of population density of different countries are below. Lists of other population densities are in See also section.'' == Biological population densities == Population density is population divided by total land area or water volume, as appropriate.〔 Low densities may cause an extinction vortex and lead to further reduced fertility. This is called the Allee effect after the scientist who identified it. Examples of the causes in low population densities include:〔(Minimum viable population size ). Eoearth.org (March 6, 2010). Retrieved on December 10, 2011.〕 * Increased problems with locating sexual mates * Increased inbreeding 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「population density」の詳細全文を読む スポンサード リンク
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