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In population genetics and population ecology, population size (usually denoted N) is a countable quantity representing the number of individual organisms in a population. Population size is directly associated with amount of genetic drift , and is the underlying cause of effects like population bottlenecks and the founder effect . [ 1 ]
The effective population size (N e) is the size of an idealised population that would experience the same rate of genetic drift as the real population. [1] Idealised populations are those following simple one- locus models that comply with assumptions of the neutral theory of molecular evolution .
Population dynamics is the type of mathematics used to model and study the size and age composition of populations as dynamical systems. Population dynamics is a branch of mathematical biology , and uses mathematical techniques such as differential equations to model behaviour.
In conservation biology, minimum viable population (MVP) size helps to determine the effective population size when a population is at risk for extinction. [5] [6] The effects of a population bottleneck often depend on the number of individuals remaining after the bottleneck and how that compares to the minimum viable population size.
This term is commonly used in the fields of biology, ecology, and conservation biology. MVP refers to the smallest possible size at which a biological population can exist without facing extinction from natural disasters or demographic, environmental, or genetic stochasticity. [1]
Population size can be influenced by the per capita population growth rate (rate at which the population size changes per individual in the population.) Births, deaths, emigration, and immigration rates all play a significant role in growth rate. The maximum per capita growth rate for a population is known as the intrinsic rate of increase.
Mark and recapture is a method commonly used in ecology to estimate an animal population's size where it is impractical to count every individual. [1] A portion of the population is captured, marked, and released. Later, another portion will be captured and the number of marked individuals within the sample is counted.
It then became a term used generally in biology in the 1870s, being most developed in wildlife and livestock management in the early 1900s. [9] It had become a staple term in ecology used to define the biological limits of a natural system related to population size in the 1950s. [8] [9]