In biology, plant and animal populations are studied, in particular, in a branch of ecology known as population biology, and in population genetics. In population dynamics, size, age and sex structure, mortality, reproductive behaviour, and growth of a population are studied. In biology, an isolated population denotes a breeding group whose members breed mostly or solely among themselves, usually as a result of physical isolation, although biologically they could breed with any members of the species. Metapopulation is a group of sub-populations in a given area, where the individuals of the various sub-populations are able to cross uninhabitable areas of the region. Biological dispersal is one of the key elements affecting in such populations.

Demography is the study of human populations. Various aspects of human behavior in populations are studied in sociology, economics, and geography. Study of populations is almost always governed by the laws of probability, and the conclusions of the studies may thus not always be applicable to some individuals. This odd factor may be reduced by statistical means, but such a generalization may be too vague to imply anything. Demography is used extensively in marketing, which relates to economic units, such as retailers, to potential customers. For example, Starbucks, a coffee shop company that wants to sell to a younger audience, looks at the demographics of an area to be able to appeal to this younger audience.

Population density

Population density is measured by dividing the number of individuals by the area of the region in which they live.

Some observers of human societies believe that the concept of carrying capacity also applies to the human population of the Earth, and that unchecked population growth can result in a "Malthusian catastrophe." Others dispute this view. The graph to the right depicts logistic growth of population.

Populate, as a verb, means the process of populating a geographic area, as by procreation or immigration.

The countries with the highest population density are microstates: Monaco, Singapore, the Vatican City, and Malta. Among larger-sized countries, Japan and Bangladesh have two of the highest population densities.

Population pyramid

This type of chart displays the development of a population over a period of time. Nations with low infant mortality and high longevity will display a more rectangular shape as a majority of the population living to old age. The converse will have a more pyramidal shape with a wide base, reflecting higher infant mortality and greater risk of early death.

Population growth

Under-population

In biology, a rarely occurring situation in which a group of individuals of a species appear in a new, inhabitable area suitable for more individuals, and begin to populate it. This may also happen if individuals of a species have been transferred to new areas on purpose or by accident. Ecological niches are usually populated, but evolution of a species may enable it to overcome the difficulties encountered in an initially hostile environment.

Under-population occurs when there are more resources in an area for example, food, energy and minerals than can be used by the people living there. Hence, the maximum human potential of that area is not realized as the resources are not fully exploited and therefore a high standard of living is not attained. Countries like Canada and Australia can export the surplus of food, energy, and mineral resources, have high incomes, good living conditions and level of technology and immigration. It is probable that standards of living would rise through increased production and exploitation of resources if population were to increase.

Under population is sometimes caused by population decline of an area. For example, rural areas close to major cities in advanced countries such as the UK are under-populated due to outward migration. In the UK, the South West Wales and the highlands of Scotland are under-populated as compared to the rest of the country. This has also happened in older declining industrial areas and the outward movement or migration has been due to lower wages and unemployment. This results in a decline in a population and with fewer people, there is a decrease in demands for services. The lower level of services therefore encourages further outward migration.

However, when making comparisons on a global scale, there does not seem to be any direct correlation between population density and over- or under-population. For example, north-east Brazil is 'over-populated' with two people per square kilometer, whereas California is 'under-populated' with over 500 people per square kilometer. Therefore, this is related to the amount of available resources. Similarly, population density is not necessarily related to the GDP per capita. The Netherlands and Germany, for example, both have a high GDP per capita and a high population density whereas Canada and Australia have a high GDP per capita and a low population density, while Bangladesh has low GDP per capita and a high population density, etc.

The balance of population and resources within a country may be uneven. For example, a country may have a population, which is too great for one resource such as energy, yet too small to use fully a second such as food supply. The relationship between population and resources are highly complex and the terms "over-population" and "under-population" must therefore be used with extreme care.

Tackling under-population

Various attempts to tackle under-population have been made:

• Improving communication networks and transport facilities makes remote places more accessible. This strategy was used in developing countries like Nigeria and Tanzania where modern railway networks were established, but these attempts were not very successful.
• Establishment of new capital cities, new towns, or development growth points. For example, Brazil has a population imbalance between the coastal parts from east and south and the rest of the country. Brasilia, the new capital was created in the 1960s in the country's geograpical center to attract people into the North and Center-West regions, but this had limited effect, as most of these unpopulated areas are occupied by large forests and swamps.
• Regional development programs. In Brazil, the interior improvement of transport networks and development of secondary growth points and rural development have all been enhanced to attract more people and discourage out-migration. The standard of living in such regions is expected to gradually improve due to improved resource utilization.

Carrying capacity and population ceiling

Carrying capacity is the largest number of people that can be adequately supported by a given area of land. It is also called the saturation level or population ceiling, a concept first suggested by Thomas Malthus.

Carrying capacity is related to available resources and existing level of technology. This ecological concept has been applied to sustainable management of the environment. Carrying capacity is more or less similar to optimum population and it is dynamic. It may increase due to economic progress, technological advances or discovery of resources.

Population control

Population control is the practice of curtailing population increase, usually by reducing the birth rate. Surviving records from Ancient Greece document the first known examples of population control. These include the colonization movement, which saw Greek outposts being built across the Mediterranean and Black Sea basins to accommodate the excess population of individual states. An important example of mandated population control is China's one-child policy, in which having more than one child is made extremely unattractive. This has led to allegations that practices like infanticide, forced abortions, and forced sterilization are used as a result of the policy.

In ecology, population control is on occasions considered to be done solely by predators, diseases, parasites, and environmental factors. At many times human effects on animal and plant populations are also considered. See also ^*. Migrations of animals may be seen as a natural way of population control, for the food on land is more abundant on some seasons. The area of the migrations' start is left to reproduce the food supply for large mass of animals next time around. See also immigration.

Population decline

Population decline is a decrease in a region's population. It can be caused by sub-replacement fertility, heavy emigration, or more dramatically disease, famine, or war. In the past, population decline was mostly caused by disease. The Black Death in Europe and the arrival of Old World diseases to the Americas all caused massive population declines. In recent years, the population of Russia and 17 other ex-communist countries began to decline (1995-2005).

In biology, population decline of a species is usually described as a result of gradually worsening environmental factors, such as prolonged drought or loss of inhabitable areas for the studied species. These, or other factors, may lead to a small population, in which case genetic factors may become dominant in the survival, or extinction of a population.

Population transfer

biological aspects, see introduced species

Population transfer is a policy by which a state forces the movement of a large group of people from onr region to another, often on the basis of their ethnicity or religion. This has occurred in India and Pakistan, between Turkey and Greece, and in Eastern Europe after the Second World War. Other movements in population are caused by immigration, such as the immigration from Europe to European colonies in the Americas, Africa, Australia and other places.

Population bomb

A best-selling work, The Population Bomb (1968) by Paul R. Ehrlich predicted disaster for humanity due to overpopulation and the "population explosion".

Thomas Malthus made a similar argument in An Essay on the Principle of Population (1798), that population is subject to exponential growth and will outstrip food supply resulting in famine. A key difference was Ehrlich's introduction of the Impact formula:

Impact = Population x Affluence x Technology

Hence, Ehrlich argues, affluent technological nations have a greater per capita impact than poorer nations.

A "population bomb," as defined in the book, requires three things: a rapid rate of change; a limit of some sort; and delays in perceiving the limit. The book's specific prediction that "in the 1970s and 1980s hundreds of millions of people will starve to death" did not come to pass, due for the most part to the efforts of Norman Borlaug's "Green Revolution" of the 1960s.

In 1972, the Club of Rome more or less repeated the argument in Limits to Growth.

Later Keith Greiner showed (1994) that Ehrlich's projections could not possibly have held the scrutiny of time, because Ehrlich applied the financial compound interest formula to population growth. Using two sets of assumptions based on Ehrlich's hypothesis, he showed that the theorized wild growth in population and subsequent scarcity of resources could not have occurred on Ehrlich's time schedule.

Liberal thinkers like Julian Lincoln Simon have also argued that overpopulation is not a legitimate concern. Rather than leading to poverty, Simon in effect argues population is one reason why prosperity exists.

World population

According to estimates published by the United States Census Bureau, the world population hit 6.5 billion (6,500,000,000) on February 25th, 2006, at 7:16 p.m. Eastern Standard Time. On October 18th, 2012 at 4:36 p.m. Eastern Daylight Time, the Earth will be home to 7 billion people. The United Nations Population Fund designated October 12, 1999 as the approximate day on which world population reached six billion. This was about 12 years after world population reached five billion, in 1987. However, given that the population of some countries, such as Nigeria, is not even known to the nearest million, such precise timings are essentially meaningless.

Countries by population

About 4 billion of the world's 6.5 billion people live in Asia. Seven of the world's ten largest countries by population are in Asia (although Russia is also located in Europe).

See also

• Population density
• List of countries by population
• List of religious populations
• List of selected cities by population density
• 1907 populations
• Biological dispersal
• Epidemiology
• Human geography
• Idealised population
• Optimum population
• Population bottleneck
• Population coding
• Population genetics
• Population health
• Population momentum
• Population pyramid
• Small population size
• Stellar population(52)

References

• Proceedings of the United Nations Expert Meeting on World Population to 2300

External links

• The Optimum Population Trust. A reliable and intelligent source of population information.
• Phishare.org (2005). Population and Health InfoShare. Retrieved February 13, 2005.
• Population Reference Bureau (2005). Retrieved February 13, 2005.
• Populationworld.com (2005). Population World: Population of World. Retrieved February 13, 2004.
• United Nations (2004). Population Division, Department of Economic and Social Affairs. Retrieved February 13, 2004.
• United States Census Bureau (2005). Census Bureau - Countries Ranked by Population. Retrieved February 13, 2005.
• PopulationData.net (2005). PopulationData.net - Informations and maps about populations around the world. Retrieved March 4, 2005.
• World Population Clock (French) WorldPopClock.com - World population clock.
• World Population Clock (English) - US Census

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