Population

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In biology, a population of organisms is a group of individuals of the same species, defined by a discontinuity or disjunction from other groups of individuals in certain characteristics, such as living area, genetic attributes, demographic structure. [1] Among biologists, the term definition varies, in some cases significantly, and sometimes those variations can be confusing. [1] There are also plenty of other terms to describe groups of individuals if no clear disjunction is present. [1] Commonly, a population can be described by what individuals constitute the population, its size, a geographical area it occupies, and the time within which the population is examined. [2] In qualitative terms, it is usually defined like "a group of organisms of the same species occupying a particular space at a particular time". [3] [4]

Contents

The two main approaches to define a population are ecological and evolutionary. From the ecological perspective, individuals are considered interacting and competing in a certain geographic area. From the evolutionary (genetic) perspective, genes and reproduction are considered the driving forces of a population. [4] Since each population has its own gene pool that changes and adapts to the environment over time, the population is considered to be the main organizational unit in biology. [5]

Etymology

The word population is derived from the Late Latin populatio (a people, a multitude), which itself is derived from the Latin word populus (a people). [6]

Terminology

There is no standard terminology to define a population, but there are many definitions of this term. [1] Aside from biology, a population can be commonly defined as a group of units. [1] In biology, those units are individuals. And such a group is separated from other groups by some characteristics (i.e. disjunct from other groups). [1] Populations can be demographically, spatially, or genetically disjunct from each other. [1] Before the 1940s–1950s, [7] the population term was used by biologists and ecologists to describe multiple species of a region, like a population of birds, [8] but the term evolved and is not used this way anymore, describing only members of the same species. [1] Although the term polyspecific population was proposed by some ecologists, but in ecology, the term community is generally used to describe multiple species of a region instead. [9] [10]

Also, there are at least 30 other terms to describe a group of individuals. [1] Some of these terms were introduced because the definitions of the population term were not clear. [1] If individuals of a group are semi-isolated from other groups, or they are more genetically similar, then the term deme can be used. [1] Groups that are not disjunct from other individuals can simply be called groups, or they also can be called subpopulations or local populations. [1] For individuals that are spatially closer to each other than to other individuals, the terms aggregation and cluster can be used. [1] Spatially separated populations of the same species can be called a metapopulation. [1] And all the populations or metapopulations of a species can be called a species population. [1]

In biology (particularly, in evolutionary biology [11] ), a population is sometimes defined as a set of individuals that interbreed or that are able to interbreed. [1] In this context, interbreeding individuals are those individuals that can produce an offspring with combined genetic material from both parents. [12] Different populations of the same species are also able to interbreed. [12] But if there are some barriers that prevent interbreeding between different populations, such barriers are called reproductive isolation. [12] In context of these terms, a species can be defined as a group of one or more interbreeding populations when such a group is reproductively isolated. [12]

Use of the term

Ecology

In ecology, a population is a group of organisms of the same species which inhabit the same geographical area and are capable of interbreeding. [13] [14] The area of a sexual population is the area where interbreeding is possible between any opposite-sex pair within the area and more probable than cross-breeding with individuals from other areas. [15] Ecology studies populations of different species rather than populations of a single species. Such populations as a whole constitute a community. Each community consists of populations of animals and plants that live together, interacting and being dependent on each other. So in ecology, a population of a single species is studied in the context of a community. [16]

In ecology, the population of a certain species in a certain area can be estimated using the Lincoln index to calculate the total population of an area based on the number of individuals observed.

Census, being defined as a complete count of individuals, is rarely possible to conduct in large populations, but it can be useful in small population that are easy to count, particularly, in applied ecology. [17]

Dynamics

This section is an excerpt from Population dynamics.[ edit ]
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. Population dynamics is also closely related to other mathematical biology fields such as epidemiology, and also uses techniques from evolutionary game theory in its modelling.

Genetics

In genetics, a population is often defined as a set of organisms in which any pair of members can breed together. They can thus routinely exchange gametes in order to have usually fertile progeny, and such a breeding group is also known therefore as a gamodeme. This also implies that all members belong to the same species. [18] If the gamodeme is very large (theoretically, approaching infinity), and all gene alleles are uniformly distributed by the gametes within it, the gamodeme is said to be panmictic. Under this state, allele (gamete) frequencies can be converted to genotype (zygote) frequencies by expanding an appropriate quadratic equation, as shown by Sir Ronald Fisher in his establishment of quantitative genetics. [19]

This seldom occurs in nature: localization of gamete exchange – through dispersal limitations, preferential mating, cataclysm, or other cause – may lead to small actual gamodemes which exchange gametes reasonably uniformly within themselves but are virtually separated from their neighboring gamodemes. However, there may be low frequencies of exchange with these neighbors. This may be viewed as the breaking up of a large sexual population (panmictic) into smaller overlapping sexual populations. This failure of panmixia leads to two important changes in overall population structure: (1) the component gamodemes vary (through gamete sampling) in their allele frequencies when compared with each other and with the theoretical panmictic original (this is known as dispersion, and its details can be estimated using expansion of an appropriate binomial equation); and (2) the level of homozygosity rises in the entire collection of gamodemes. The overall rise in homozygosity is quantified by the inbreeding coefficient (f or φ). All homozygotes are increased in frequency – both the deleterious and the desirable. The mean phenotype of the gamodemes collection is lower than that of the panmictic original – which is known as inbreeding depression. It is most important to note, however, that some dispersion lines will be superior to the panmictic original, while some will be about the same, and some will be inferior. The probabilities of each can be estimated from those binomial equations. In plant and animal breeding, procedures have been developed which deliberately utilize the effects of dispersion (such as line breeding, pure-line breeding, backcrossing). Dispersion-assisted selection leads to the greatest genetic advance (ΔG=change in the phenotypic mean), and is much more powerful than selection acting without attendant dispersion. This is so for both allogamous (random fertilization) [20] and autogamous (self-fertilization) gamodemes. [21]

World human population

According to the UN, the world's population surpassed 8 billion on 15 November 2022, [22] an increase of 1 billion since 12 March 2012. According to a separate estimate by the United Nations, Earth's population exceeded seven billion in October 2011. According to the United Nations Population Fund (UNFPA), growth to such an extent offers unprecedented challenges and opportunities to all of humanity. [23]

According to papers published by the United States Census Bureau, the world population hit 6.5 billion on 24 February 2006. The United Nations Population Fund designated 12 October 1999 as the approximate day on which world population reached six billion. This was about 12 years after the world population reached five billion in 1987, and six years after the world population reached 5.5 billion in 1993. The population of countries such as Nigeria is not even known to the nearest million, [24] so there is a considerable margin of error in such estimates. [25]

Researcher Carl Haub calculated that a total of over 100 billion people have probably been born in the last 2000 years. [26]

Predicted growth and decline

The years taken for every billion people to be added to the world's population, and the years that population was reached (with future estimates). World population growth - time between each billion-person growth.svg
The years taken for every billion people to be added to the world's population, and the years that population was reached (with future estimates).

Population growth increased significantly as the Industrial Revolution gathered pace from 1700 onwards. [27] The last 50 years have seen a yet more rapid increase in the rate of population growth [27] due to medical advances and substantial increases in agricultural productivity, particularly beginning in the 1960s, [28] made by the Green Revolution. [29] In 2017 the United Nations Population Division projected that the world's population would reach about 11.6 billion in 2050 and 24.8 billion in 2100. [30]

PRB 2017 Data Sheet Largest Populations PRB 2017 Data Sheet Largest Populations.jpg
PRB 2017 Data Sheet Largest Populations

In the future, the world's population is expected to peak at some point, [31] after which it will decline due to economic reasons, health concerns, land exhaustion and environmental hazards. According to one report, it is very likely that the world's population will stop growing before the end of the 21st century. Further, there is some likelihood that population will actually decline before 2100.[ The date at which it stops growing is the exact same date when it starts to decline. ] [32] [33] Population has already declined in the last decade or two in Eastern Europe, the Baltics and in the former Commonwealth of Independent States. [34]

The population pattern of less-developed regions of the world in recent years has been marked by gradually declining birth rates. These followed an earlier sharp reduction in death rates. [35] This transition from high birth and death rates to low birth and death rates is often referred to as the demographic transition. [35]

Population planning

Human population planning is the practice of changing the rate of growth of a human population. Historically, human population control has been implemented with the goal of limiting the rate of population growth. In the time from the 1950s to the 1980s, concerns about global population growth and its effects on poverty, environmental degradation, and political stability led to efforts to reduce population growth rates. While population control can involve measures that make people's lives better by giving them greater control of their reproduction, a few programs, most notably the Chinese government's one-child per family policy, have resorted to coercive measures.

In the 1970s, tension grew between population control advocates and women's health activists who advanced women's reproductive rights as part of a human rights-based approach. [36] Growing opposition to the narrow population control focus led to a significant change in population control policies in the early 1980s. [36]

See also

References

  1. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Wells, Jeffrey V.; Richmond, Milo E. (1995). "Populations, Metapopulations, and Species Populations: What Are They and Who Should Care?". Wildlife Society Bulletin. 23 (3): 458–462. ISSN   0091-7648. JSTOR   3782955.
  2. ↑ Rastogi, V. B.; Kishore, B. (1997). A Complete Course in ISC Biology. Pitambar Publishing. pp. 19–21. ISBN   978-81-209-0822-2.
  3. ↑ Krebs, Charles J. (1972). Ecology: The Experimental Analysis of Distribution and Abundance. Harper & Row. ISBN   978-0-06-043770-1.
  4. 1 2 Waples, Robin S.; Gaggiotti, Oscar (2006). "INVITED REVIEW: What is a population? An empirical evaluation of some genetic methods for identifying the number of gene pools and their degree of connectivity". Molecular Ecology. 15 (6): 1419–1439. Bibcode:2006MolEc..15.1419W. doi:10.1111/j.1365-294X.2006.02890.x. ISSN   1365-294X. PMID   16629801.
  5. ↑ Young, Allen M. (6 December 2012). Population Biology of Tropical Insects. Springer Science & Business Media. p. 22. ISBN   978-1-4684-1113-3.
  6. ↑ "population | Etymology, origin and meaning of population by etymonline". etymonline.com. Retrieved 8 June 2023.
  7. ↑ Yablokov, A. V.; Korenberg, Ėduard Isaevich (1989). Population Principles in Research Into Natural Focality of Zoonoses. CRC Press. pp. 255–256. ISBN   978-3-7186-4978-5.
  8. ↑ McIntosh, Robert P. (26 September 1986). The Background of Ecology: Concept and Theory. Cambridge University Press. p. 150. ISBN   978-0-521-27087-8.
  9. ↑ Manglik, Mr Rohit (24 March 2024). Fundamentals of Environmental Sciences. EduGorilla Publication. ISBN   978-93-7093-345-3.
  10. ↑ Sharma, P. D.; P.D, Sharma (2009). Ecology And Environment. Rastogi Publications. p. 112. ISBN   978-81-7133-905-1.
  11. ↑ Walton, Andy; Aylward, Alex; Thomas, Mark G.; Rutherford, Adam (September 2025). "The History of the Panmictic Population Concept and Its Legacy in Contemporary Population Genetics". Annals of Human Genetics. 89 (5): 274–284. doi:10.1111/ahg.70015. ISSN   1469-1809. PMC   12336970 . PMID   40719227.
  12. 1 2 3 4 Minkoff, Eli; Hood-DeGrenier, Jennifer K. (24 July 2023). Biology Trending: A Contemporary Issues Approach. CRC Press. ISBN   978-1-000-87794-6.
  13. ↑ "Population". Biology Online. Retrieved 5 December 2012.
  14. ↑ "Definition of population (biology)". Oxford Dictionaries. Oxford University Press. Archived from the original on 10 May 2013. Retrieved 5 December 2012. a community of animals, plants, or humans among whose members interbreeding occurs
  15. ↑ Hartl, Daniel (2007). Principles of Population Genetics. Sinauer Associates. p. 45. ISBN   978-0-87893-308-2.
  16. ↑ Serrano Sanchez, C. (1 April 1996). "Introduction: The concept of population". International Journal of Anthropology. 11 (2): 15–18. doi:10.1007/BF02441407. ISSN   1824-3096.
  17. ↑ Conroy, Michael J.; Carroll, John P. (20 September 2011). Quantitative Conservation of Vertebrates. John Wiley & Sons. p. 74. ISBN   978-1-4443-5649-6.
  18. ↑ Hartl, Daniel (2007). Principles of Population Genetics. Sinauer Associates. p. 95. ISBN   978-0-87893-308-2.
  19. ↑ Fisher, R. A. (1999). The Genetical Theory of Natural Selection. Oxford University Press (OUP). ISBN   978-0-19-850440-5.
  20. ↑ Gordon, Ian L. (2000). "Quantitative genetics of allogamous F2 : an origin of randomly fertilized populations". Heredity . 85 (1): 43–52. Bibcode:2000Hered..85...43G. doi: 10.1046/j.1365-2540.2000.00716.x . PMID   10971690.
  21. ↑ Gordon, Ian L. (2001). "Quantitative genetics of autogamous F2". Hereditas . 134 (3): 255–262. doi: 10.1111/j.1601-5223.2001.00255.x . PMID   11833289.
  22. ↑ "Population Clock". www.worldometers.info. Archived from the original on 15 November 2022. Retrieved 15 November 2022.
  23. ↑ to a World of Seven Billion People (Archived 13 January 2012 at the Wayback Machine ). UNFPA, 12 September 2011.
  24. ↑ "Cities in Nigeria: 2005 Population Estimates – MongaBay.com" . Retrieved 1 July 2008.
  25. ↑ "Country Profile: Nigeria". BBC News. 24 December 2009. Retrieved 1 July 2008.
  26. ↑ Haub, C. 1995/2004. "How Many People Have Ever Lived on Earth?" Population Today, "How Many People Have Ever Lived on Earth? - Population Reference Bureau". Archived from the original on 24 April 2013. Retrieved 29 April 2013.
  27. 1 2 As graphically illustrated by population since 10,000BC and population since 1000AD
  28. ↑ "The end of India's green revolution?". BBC News. 29 May 2006. Retrieved 29 November 2009.
  29. ↑ Food First/Institute for Food and Development Policy (Archived 14 July 2009 at the Wayback Machine )
  30. ↑ "UN Population Prospects 2017" (PDF).
  31. ↑ World Population Development Statistics: Forecast, United Nations, 2011.
  32. ↑ Lutz, Wolfgang; Sanderson, Warren; Scherbov, Sergei (2001). "The End of World Population Growth" (PDF). Nature. 412 (6846): 543–545. Bibcode:2001Natur.412..543L. doi:10.1038/35087589. PMID   11484054. S2CID   4425080.
  33. ↑ Ojovan, M.I.; Loshchinin, M.B. (2015). "Heuristic Paradoxes of S.P. Kapitza Theoretical Demography". European Researcher. 92 (3): 237–248. doi: 10.13187/er.2015.92.237 .
  34. ↑ "world demographic trends". gsociology.icaap.org. Retrieved 18 July 2019.
  35. 1 2 "Human Population Growth". Archived from the original on 30 March 2009. Retrieved 7 April 2009.
  36. 1 2 Knudsen, Lara (2006). Reproductive Rights in a Global Context . Vanderbilt University Press. pp.  2. ISBN   978-0-8265-1528-5. reproductive rights.

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