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In population genetics and population ecology, population size (usually denoted N) is the number of individual organisms in a population.

The effective population size (Ne) is defined as "the number of breeding individuals in an idealized population that would show the same amount of dispersion of allele frequencies under random genetic drift or the same amount of inbreeding as the population under consideration." Ne is usually less than N (the absolute population size) and this has important applications in conservation genetics.

Small population size results in increased genetic drift. Population bottlenecks are when population size reduces for a short period of time.

Overpopulation may indicate any case in which the population of any species of animal may exceed the carrying capacity of its ecological niche.

See also[edit]

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682 news items

BBC News

BBC News
Mon, 11 Aug 2014 06:11:28 -0700

As the people of Scotland weigh up how to vote in the independence referendum, they are asking questions on a range of topics from the economy to welfare. In this series, we are looking at those major questions and by using statistics, analysis and ...

University Herald

University Herald
Tue, 02 Sep 2014 02:22:30 -0700

"Climate change is threatening the already small population size." Devils Hole is a water-laden limestone cavern in the Ash Meadows National Wildlife Refuge. Its water temperatures and dissolved oxygen concentrations have reached lethal limits for most ...
Washington Post (blog)
Tue, 02 Sep 2014 11:11:15 -0700

26-30 at 127 locations chosen in accordance with their population size (the sampling error is three percentage points). Studies have shown that during times of conflict, public opinion becomes more hawkish and nationalistic – what has been termed the ...
Chillicothe Gazette
Tue, 02 Sep 2014 17:33:45 -0700

The information collected will be used to help determine migration flight patterns and timing, survival rates, weather influences on migration, and the overall population size of monarch butterflies. The program is being presented in conjunction with ...
CNN (blog)
Mon, 01 Sep 2014 17:27:34 -0700

This cold snap would have made life difficult for our African ancestors, and the genetic evidence points to a sharp reduction in population size around this time. In fact, the human population likely dropped to fewer than 10,000. We were holding on by ...

The New Republic

The New Republic
Wed, 13 Aug 2014 14:56:15 -0700

Generally, police forces get less diverse as you move down in population size. Of course, these are just averages and they do not take into account the diversity of the cities themselves. Research also suggests, though, that representation makes a ...
Himalayan Times
Tue, 02 Sep 2014 01:15:28 -0700

The PRF report also gives 16 population, health and environment indicators for more than 200 countries. “World population is forecast to rise from 7.2 billion today to 9.7 billion by 2050. India is projected to pass China in population size in about 15 ...


Tue, 02 Sep 2014 07:20:02 -0700

"At present, researchers use expensive, invasive techniques to track the population size and health of wildlife such as polar bears. Using footprint DNA, we could dramatically cut the investment required, so monitoring populations could be done more ...

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