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Quasi-extinction refers to the state in which a species or population has declined to critically low numbers, making its recovery highly unlikely, even though a small number of individuals may still persist. This concept is often used in conservation biology to identify species at extreme risk of extinction and to guide management strategies aimed at preventing complete extinction. Quasi-extinction is typically characterized by an inability of the population to sustain itself due to genetic, demographic, or environmental factors.

Extinction threshold

The quasi-extinction threshold, or sometimes called the quasi-extinction risk is the population size below which a species is considered to be at extreme risk of quasi-extinction. This threshold varies by species and is influenced by several factors, including reproductive rates, habitat requirements, and genetic diversity. It is often used in population viability analyses (PVA) to model the likelihood of a species declining to levels where recovery becomes nearly impossible.

References

1. Engen, S.; Saether, B. E. (2000-08-21). "Predicting the time to quasi-extinction for populations far below their carrying capacity". Journal of Theoretical Biology. 205 (4): 649–658. doi:10.1006/jtbi.2000.2094. ISSN 0022-5193. PMID 10931759.
2. Block, G. L.; Allen, L. J. (March 2000). "Population extinction and quasi-stationary behavior in stochastic density-dependent structured models". Bulletin of Mathematical Biology. 62 (2): 199–228. doi:10.1006/bulm.1999.0147. ISSN 0092-8240. PMID 10824427.
3. Engelson, Andrew (2021-12-16). "What does 'quasi-extinction' actually mean?". Columbia Insight. Retrieved 2024-12-16.
4. Legendre, Stéphane; Schoener, Thomas; Clobert, Jean; Spiller, David (August 2008). "How Is Extinction Risk Related to Population‐Size Variability over Time? A Family of Models for Species with Repeated Extinction and Immigration". The American Naturalist. 172 (2): 282–298. doi:10.1086/589454. ISSN 0003-0147.
5. Morris, W. F.; Doak, D. F. (22 June 2002). Quantitative conservation biology: Theory and practice of population viability analysis. Sunderland, Massachusetts, USA: Sinauer Associates. ISBN 9780878935468.
6. Holmes, Elizabeth Eli; Sabo, John L.; Viscido, Steven Vincent; Fagan, William Fredric (December 2007). "A statistical approach to quasi-extinction forecasting". Ecology Letters. 10 (12): 1182–1198. doi:10.1111/j.1461-0248.2007.01105.x. ISSN 1461-0248. PMID 17803676.
7. Ludwig, Donald (1996). "Uncertainty and the Assessment of Extinction Probabilities". Ecological Applications. 6 (4): 1067–1076. doi:10.2307/2269591. ISSN 1939-5582.

v t e Extinction
Phenomena	Background extinction rate Coextinction De-extinction Ecological extinction Extinct in the wild Functional extinction Genetic pollution Lazarus taxon Local extinction Pseudoextinction
Models	Extinction vortex
Causes	Climate variability and change Genetic erosion Invasive species Habitat destruction Human impact on the environment Muller's ratchet Mutational meltdown Overabundant species Overexploitation Overshoot Paradox of enrichment
Theories and concepts	Extinction debt Extinction risk from climate change Extinction threshold Quasi-extinction Field of Bullets Hypothetical species Latent extinction risk Living fossil
Extinction events	Major Ordovician–Silurian Late Devonian Permian–Triassic Triassic–Jurassic Cretaceous–Paleogene Holocene Timeline Other Great Oxidation End-Ediacaran End-Botomian Dresbachian Cambrian–Ordovician Ireviken Mulde Lau Carboniferous Olson's End-Capitanian Carnian Pluvial Toarcian End-Jurassic or Tithonian Aptian Cenomanian-Turonian Eocene–Oligocene Middle Miocene Pliocene–Pleistocene Quaternary
Extinct species	Lists of extinct species IUCN Red List extinct species
Organizations	International Union for Conservation of Nature IUCN Species Survival Commission Extinction Rebellion Voluntary Human Extinction Movement
See also	Anthropocene Decline in amphibian populations Decline in insect populations Extinction symbol Human extinction The Sixth Extinction: An Unnatural History
Category [REDACTED] Commons

v t e Deforestation and desertification
Deforestation	Assarting Deforestation Deforestation and climate change Deforestation by region Illegal logging Mountaintop removal Slash-and-burn Slash-and-char
Desertification	Aridification Historic desertification Moisture recycling Soil retrogression and degradation Water scarcity By region: China Gobi Desert Lebanon Libya Mali Mauritania Mongolia Sahel Yemen
Mitigation	Afforestation Arid Lands Information Network Biochar Conservation grazing Desert greening Ecoforestry Ecological engineering Farmer-managed regeneration Flexible Mechanisms Great Green Wall (Africa) Great Green Wall (China) Managed intensive rotational grazing Oasification Reforestation United Nations Convention to Combat Desertification
Related articles	Forest Landscape Integrity Index Forestry Intact forest landscape Land surface effects on climate Land use, land-use change and forestry List of global issues Natural landscape Terra preta Wilderness

• Extinction
• Conservation biology
• Environmental conservation
• Evolutionary biology
• IUCN Red List
• Biota by conservation status