In
population dynamics, depensation is the effect on a
population
Population typically refers to the number of people in a single area, whether it be a city or town, region, country, continent, or the world. Governments typically quantify the size of the resident population within their jurisdiction using a ...
(such as a
fish stock) whereby, due to certain causes, a decrease in the breeding population (mature individuals) leads to reduced production and survival of eggs or offspring.
The causes may include predation levels rising per offspring (given the same level of overall predator pressure) and the
Allee effect The Allee effect is a phenomenon in biology characterized by a correlation between population size or density and the mean individual fitness (often measured as ''per capita'' population growth rate) of a population or species.
History and backgro ...
, 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
Resource depletion is the consumption of a resource faster than it can be replenished. Natural resources are commonly divided between renewable resources and non-renewable resources (see also mineral resource classification). Use of either ...
), or even
local extinction.
The phenomenon of critical depensation may be modelled or defined by a negative second order
derivative
In mathematics, the derivative of a function of a real variable measures the sensitivity to change of the function value (output value) with respect to a change in its argument (input value). Derivatives are a fundamental tool of calculus. ...
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)
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Conservation biology
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Local extinction
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Overexploitation
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Overfishing
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Small population size
Small populations can behave differently from larger populations. They are often the result of population bottlenecks from larger populations, leading to loss of heterozygosity and reduced genetic diversity and loss or fixation of alleles and s ...
*
Threatened species
Threatened species are any species (including animals, plants and fungi) which are vulnerable to endangerment in the near future. Species that are threatened are sometimes characterised by the population dynamics measure of '' critical depen ...
References
External links
Optimal harvesting in the presence of critical depensationOn line source of definitions and other fish info
Extinction
Ecological processes
Population dynamics
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