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In population dynamics, depensation is the effect on a population (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.[1] The causes may include:

  • predation levels rising per offspring (given the same level of overall predator pressure)
  • the allee effect, particularly the reduced likelihood of finding a mate.

Although depensation is often considered in relation to the population being harvested (especially fish), the actual level of harvesting, by definition, is not part of depensation.[citation needed]

Critical depensation[edit]

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").[1] Ultimately this may lead to the population or fishery's collapse (resource depletion), or even local extinction.

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[edit]


  1. ^ a b Quinn, Terrance (25 March 1999). Quantitative Fish Dynamics. Oxford University Press. p. 99. 

External links[edit]