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For the use of the word population in statistics, see statistical population. In sociology and biology, a population is the collection of people, or organisms of a particular species, living in a given geographic area, or space, usually measured by a census. 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, a coffee shop 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 pyramid The age and gender distribution of a population within a given nation or region is commonly represented by means of a population pyramid. This is a triangular distribution with the portions of the population along the horizontal X-axis and the 5-year age groups (cohorts) along the vertical Y-axis. Male population is shown to the left of the vertical axis and female to the right. 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 Population growth is change in population over time, and can be quantified as the change in the number of individuals in a population per unit time. The term population growth can technically refer to any species, but almost always refers to humans, and it is often used informally for the more specific demographic term population growth rate (see below), and is often used to refer specifically to the growth of the population of the world. Doubling time The doubling time is the period of time required for a quantity to double in size or value. It is most often applied to population growth although it can be used for any increasing quantity, such as price inflation or the volume of malignant tumours. When the growth rate is constant, the quantity undergoes exponential growth (also known as geometric growth) and has a fixed doubling time which can be calculated directly from the growth rate. This time can be derived by dividing the natural logarithm of 2 by the exponent of growth, or approximated by dividing 70 by the percentage growth rate. For example, given Canada's net population growth of 0.9% in the year 2006, dividing 70 by .9 gives an approximate doubling time of 77.7 years. Thus if the growth rate remains constant, Canada's population will double from its current 33 million to 66 million by 2083. Examining the doubling time can give a more intuitive sense of the long-term impact of growth than simply viewing the percentage growth rate. 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. In biology, a rarely occurring situation is one 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. Population decline is recognized 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. 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. Some rural areas close to major cities in advanced countries such as the UK are under-populated due to outward migration. In the UK, the Southwest Wales and the highlands of Scotland are less densely populated 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 phenomenon results in a decline in a population. With fewer people, there is a decrease in demands for services. The lower level of services therefore sometimes 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 portions of California may have further carrying capacity 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. Various attempts to address population decline have been made: 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 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 one 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. In modern times, the region of Tibet has undergone heavy population transfer from the coastal regions of China, displacing the native Tibetans with ethnic Han Chinese. 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. 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 25 2006, at 7:16 p.m. Eastern Standard Time. On October 18 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 | |||||||
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