For more information, log on to- http://shomusbiology.weebly.com/ Download the study materials here- http://shomusbiology.weebly.com/bio-materials.html Population growth is the change in a population over time, and can be quantified as the change in the number of individuals of any species in a population using "per unit time" for measurement. In biology, the term population growth is likely to refer to any known organism, but this article deals mostly with the application of the term to human populations in demography. Population growth rates might have declined, but in 2013 every 60 minutes there are another 8,000 people in the world: about 75 million every year.[1] In demography, population growth is used informally for the more specific term population growth rate (see below), and is often used to refer specifically to the growth of the human population of the world. Simple models of population growth include the Malthusian Growth Model and the logistic model. The world population grew from 1 billion to 7 billion from 1800 to 2011. During the year 2011, according to estimates, 135 million people were born and 57 million died, for an increase in population of 78 million. In demographics and ecology, the "population growth rate" is the rate at which the number of individuals in a population increases in a given time period as a fraction of the initial population. Specifically, population growth rate refers to the change in population over a unit time period, often 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: pop\ growth\ rate = \frac{ P(t_2) - P(t_1)} {P(t_1)} The most common way to express population growth is as a percentage. That is: \mathrm{percentage\ growth} = \mathrm{pop\ growth\ rate} \times 100. A positive growth ratio (or rate) indicates that the population is increasing, while a negative growth ratio indicates the population is decreasing. A growth ratio of zero indicates that there were the same number of people at the two times—net difference between births, deaths a growth rate may be zero even when there are significant changes in the birth rates, death rates, immigration rates, and age distribution between the two times.[3] A related measure is the net reproduction rate. In the absence of migration, a net reproduction rate of more than one indicates that the population of women is increasing, while a net reproduction rate less than one (sub-replacement fertility) indicates that the population of women is decreasing. Source of the article published in description is Wikipedia. I am sharing their material. Copyright by original content developers. Link- http://en.wikipedia.org/wiki/Main_Page

• published: 13 Nov 2013
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