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Zero population growth, sometimes abbreviated ZPG, is a condition of demographic balance where the number of people in a specified population neither grows nor declines; that is, the number of births plus in-migrants equals the number of deaths plus out-migrants. [1]
Population growth is the increase in the number of people in a population or dispersed group. The global population has grown from 1 billion in 1800 to 8.2 billion in 2025. [ 3 ] Actual global human population growth amounts to around 70 million annually, or 0.85% per year.
The population of the More Developed regions is slated to remain mostly unchanged, at 1.2-1.3 billion for the remainder of the 21st century. All population growth comes from the Less Developed regions. [6] [7] The table below breaks out the UN's future population growth predictions by region [6] [7]
P 0 = P(0) is the initial population size, r = the population growth rate, which Ronald Fisher called the Malthusian parameter of population growth in The Genetical Theory of Natural Selection, [2] and Alfred J. Lotka called the intrinsic rate of increase, [3] [4] t = time. The model can also be written in the form of a differential equation:
A notable leader in the area of sub-state population projection is the World Population Program of the International Institute of Applied Systems Analysis (IIASA) in Laxenburg, Austria. Some of the issues which are studied in the context of political demography are: surges of young people in the developing world, significantly increasing aging ...
Minimum viable population (MVP) is a lower bound on the population of a species, such that it can survive in the wild. This term is commonly used in the fields of biology , ecology , and conservation biology .
The Limits to Growth (LTG) is a 1972 report [2] that discussed the possibility of exponential economic and population growth with finite supply of resources, studied by computer simulation. [3] The study used the World3 computer model to simulate the consequence of interactions between the Earth and human systems.
Malthus explains, for example, that a human check on population growth is the conscious decision not to reproduce because of financial burden. [25] Malthus then explains that the main check on population growth is food. In periods of high food availability the population increases, while in periods of food shortages, the population decreases. [26]