Critical depensation
Encyclopedia
In population dynamics
, depensation is the effect on a population
(or stock
) whereby, due to certain causes, a decrease in the breeding population (mature individuals) leads to reduced survival and production of eggs or offspring. The cause may be either:
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.
, the population or fishery's collapse, 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.
Population dynamics
Population dynamics is the branch of life sciences that studies short-term and long-term changes in the size and age composition of populations, and the biological and environmental processes influencing those changes...
, depensation is the effect on a population
Population
A population is all the organisms that both belong to the same group or species and live in the same geographical area. The area that is used to define a sexual population is such that inter-breeding is possible between any pair within the area and more probable than cross-breeding with individuals...
(or stock
Fish stock
Fish stocks are subpopulations of a particular species of fish, for which intrinsic parameters are the only significant factors in determining population dynamics, while extrinsic factors are considered to be insignificant.-The stock concept:All species have geographic limits to their...
) whereby, due to certain causes, a decrease in the breeding population (mature individuals) leads to reduced survival and production of eggs or offspring. The cause may be either:
- predation levels rising per offspring (given the same level of overall predator pressure), or
- the allee effectAllee effectThe Allee effect is a phenomenon in biology characterized by a positive correlation between population density and the per capita population growth rate in very small populations.-Description:...
, which is 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.
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 resource depletionResource depletion
Resource depletion is an economic term referring to the exhaustion of raw materials within a region. Resources are commonly divided between renewable resources and non-renewable resources...
, the population or fishery's collapse, or even local extinction
Local extinction
Local extinction, also known as extirpation, is the condition of a species which ceases to exist in the chosen geographic area of study, though it still exists elsewhere...
.
The phenomenon of critical depensation may be modelled or defined by a negative second order derivative
Derivative
In calculus, a branch of mathematics, the derivative is a measure of how a function changes as its input changes. Loosely speaking, a derivative can be thought of as how much one quantity is changing in response to changes in some other quantity; for example, the derivative of the position of a...
of population growth rate with respect of population biomass
Biomass (ecology)
Biomass, in ecology, is the mass of living biological organisms in a given area or ecosystem at a given time. Biomass can refer to species biomass, which is the mass of one or more species, or to community biomass, which is the mass of all species in the community. It can include microorganisms,...
, 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
- Abundance (ecology)Abundance (ecology)Abundance is an ecological concept referring to the relative representation of a species in a particular ecosystem. It is usually measured as the large number of individuals found per sample...
- Conservation biologyConservation biologyConservation biology is the scientific study of the nature and status of Earth's biodiversity with the aim of protecting species, their habitats, and ecosystems from excessive rates of extinction...
- Local extinctionLocal extinctionLocal extinction, also known as extirpation, is the condition of a species which ceases to exist in the chosen geographic area of study, though it still exists elsewhere...
- OverfishingOverfishingOverfishing occurs when fishing activities reduce fish stocks below an acceptable level. This can occur in any body of water from a pond to the oceans....
- OverexploitationOverexploitationOverexploitation, also called overharvesting, refers to harvesting a renewable resource to the point of diminishing returns. Sustained overexploitation can lead to the destruction of the resource...
- Small population sizeSmall population sizeSmall populations behave differently from larger populations. They often result in population bottlenecks, which have harmful consequences for the survival of that population.-Demographic effects:...
- Threatened speciesThreatened speciesThreatened species are any speciesg animals, plants, fungi, etc.) which are vulnerable to endangerment in the near future.The World Conservation Union is the foremost authority on threatened species, and treats threatened species not as a single category, but as a group of three categories,...