Depensation
{{Short description|Concept in population dynamics}}
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In population dynamics, depensation is the effect on a population (such as a fish stock{{cite journal|title=Detecting the presence of depensation in collapsed fisheries: The case of the Northern cod stock|first1=Jose M. |last1=Maroto|first2= Manuel|last2= Moran|journal=Ecological Economics|date=2014 |volume=97|page=101 |doi=10.1016/j.ecolecon.2013.11.006 |bibcode=2014EcoEc..97..101M }}) whereby, due to certain causes, a decrease in the breeding population (mature individuals) leads to reduced production and survival of eggs or offspring.{{cite book |last= Quinn|first= Terrance|date= 25 March 1999|title= Quantitative Fish Dynamics|url= https://books.google.com/books?id=5FVBj8jnh6sC&q=depensation|publisher= Oxford University Press|page= 99|isbn= 9780195360400}} The causes may include predation levels rising per offspring (given the same level of overall predator pressure) and the Allee effect, particularly the reduced likelihood of finding a mate.
Critical depensation
When the level of depensation is high enough that the population is no longer able to sustain itself, it is said to be a critical depensation. This occurs when the population size has a tendency to decline when the population drops below a certain level (known as the "Critical depensation level"). Ultimately this may lead to the population or fishery's collapse (resource depletion), or even local extinction.{{cite journal|title=Optimal Control of a Fishery under Critical Depensation|first1=Tapan Kumar |last1=Kar |first2=Swarnakamal |last2=Misra|journal=Journal of Fisheries and Aquatic Science|volume=1}}
The phenomenon of critical depensation may be modelled or defined by a negative second order derivative of population growth rate with respect of population biomass, which describes a situation where a decline in population biomass is not compensated by a corresponding increase in marginal growth per unit of biomass.
See also
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- Abundance (ecology)
- Conservation biology
- Local extinction
- Overexploitation
- Overfishing
- Small population size
- Threatened species
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References
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External links
- [http://cat.inist.fr/?aModele=afficheN&cpsidt=16127115 Optimal harvesting in the presence of critical depensation]
- [http://www.fishbase.org/search.php On line source of definitions and other fish info]
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