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 is often used informally for the more specific demographic term population growth rate (see below).

Simple models of population growth include the Malthusian Growth Model and the logistic model.

Population growth rate

---

In demographics and ecology, Population growth rate (PGR) is the fractional rate at which the number of individuals in a population increases. Specifically, PGR ordinarily refers to the change in population over a specific time period expressed as a percentage of the number of individuals in the population at the beginning of that period. This can be written as the formula:

$Population\; Growth\; Rate\; =\; \{(Birth\; Rate\; +\; Immigration)\; -\; (Mortality\; Rate\; +\; Emigration)\; \backslash over\; Population\; Size\}$

The crude death rate as defined above and applied to a whole population can give a misleading impression. For example, the number of deaths per 1000 people can be higher for developed nations than in less-developed countries, despite standards of health being better in developed countries.

Human population growth rate

---

In general the rate of human population growth has been steadily declining in the world (that is, population is growing more slowly than in the past), but growth remains high in the Middle East and Sub-Saharan Africa. Some countries have negative population growth (i.e. net decrease in population over time), especially in Central and Eastern Europe (mainly because of low fertility rates) and Southern Africa (due to the high number of HIV-related deaths). Japan and Western Europe are expected to have negative population growth as well in the coming decade because of sub-replacement fertility rates.

It has been proposed by many that population growth, if not controlled, could lead to a situation where demands for resources outstrip their ready availability (i.e. overpopulation). Conversely, a declining population can cause a situation where an aging general population can increase dramatically relative to the more productive youthful members of society (i.e. underpopulation). This has implications on many levels - not the least of which are the needs of the elderly being cared for by an ever smaller group of working adults.

See also

---

• Overpopulation
• Underpopulation
• World population
• Exponential growth
• Logistic function - concept related to logistic model.
• Ronald Fisher - who referred to the population growth rate as the Malthusian Parameter.

External links

---

• The Magnitude Of Population Growth And Its Consequences

Ecology | Demography | population

Bevölkerungswachstum | Bevolkingsgroei | Crescimento populacional