Extinction vortices are a class of models through which conservation biologists

Conservation biology

Conservation 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...

, geneticists

Conservation genetics

Conservation genetics is an interdisciplinary science that aims to apply genetic methods to the conservation and restoration of biodiversity. Researchers involved in conservation genetics come from a variety of fields including population genetics, molecular ecology, biology, evolutionary biology,...

 and ecologists can understand the dynamics of and categorize extinction

Extinction

In biology and ecology, extinction is the end of an organism or of a group of organisms , normally a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and recover may have been lost before this point...

s in the context of their causes. Developed by M. E. Gilpin and M. E. Soulé

Michael Soule

Michael E. Soulé is a U.S. biologist, best known for his work in promoting the idea of conservation biology. He earned a Ph.D. in Population Biology at Stanford University under Paul R. Ehrlich...

 in their (now) famous 1986 paper Minimum viable populations: Processes of species extinction, there are currently four classes of extinction vortices. The first two (R and D) deal with environmental

Natural environment

The natural environment encompasses all living and non-living things occurring naturally on Earth or some region thereof. It is an environment that encompasses the interaction of all living species....

 factors that have an effect on the ecosystem

Ecosystem

An ecosystem is a biological environment consisting of all the organisms living in a particular area, as well as all the nonliving , physical components of the environment with which the organisms interact, such as air, soil, water and sunlight....

 or community

Community

The term community has two distinct meanings:*a group of interacting people, possibly living in close proximity, and often refers to a group that shares some common values, and is attributed with social cohesion within a shared geographical location, generally in social units larger than a household...

 level, such as disturbance

Disturbance

In ecology, a disturbance is a temporary change in average environmental conditions that causes a pronounced change in an ecosystem. Outside disturbance forces often act quickly and with great effect, sometimes resulting in the removal of large amounts of biomass...

, pollution

Pollution

Pollution is the introduction of contaminants into a natural environment that causes instability, disorder, harm or discomfort to the ecosystem i.e. physical systems or living organisms. Pollution can take the form of chemical substances or energy, such as noise, heat or light...

, habitat loss etc. Whereas the second two (F and A) deal with genetic factors such as inbreeding depression

Inbreeding depression

Inbreeding depression is the reduced fitness in a given population as a result of breeding of related individuals. It is often the result of a population bottleneck...

 and outbreeding depression

Outbreeding depression

A concept in selective breeding and zoology, outbreeding depression refers to cases when offspring from crosses between individuals from different populations have lower fitness than progeny from crosses between individuals from the same population....

, genetic drift

Genetic drift

Genetic drift or allelic drift is the change in the frequency of a gene variant in a population due to random sampling.The alleles in the offspring are a sample of those in the parents, and chance has a role in determining whether a given individual survives and reproduces...

 etc.

Types of vortices

• R Vortex: The R vortex is initiated when there is a disturbance which facilitates a lowering of 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...
  
   size (N) and a corresponding increase in variability (Var(r)). This event can make populations vulnerable to additional disturbances which will lead to further decreases in population size (N) and further increases in variability (Var(r)). A prime example of this would be the disruption of sex ratio
  Sex ratio
  Sex ratio is the ratio of males to females in a population. The primary sex ratio is the ratio at the time of conception, secondary sex ratio is the ratio at time of birth, and tertiary sex ratio is the ratio of mature organisms....
  
  s in a population away from the species optimum.

• D Vortex: The D vortex is initiated when population size (N) decreases and variability (Var(r)) increases such that the spatial distribution (D) of the population is increased and the population becomes "patchy" or fragmented
  Habitat fragmentation
  Habitat fragmentation as the name implies, describes the emergence of discontinuities in an organism's preferred environment , causing population fragmentation...
  
  . Within these fragments, local extinction rates increase which, through positive feedback
  Positive feedback
  Positive feedback is a process in which the effects of a small disturbance on a system include an increase in the magnitude of the perturbation. That is, A produces more of B which in turn produces more of A. In contrast, a system that responds to a perturbation in a way that reduces its effect is...
  
  , further increases D.

• F Vortex: The F vortex is initiated by a decrease in population size (N) which leads to a decrease in individual heterozygosity (an increase in autozygosity) and increases the rate of genetic drift, resulting in increased degrees of inbreeding depression and an increase in population genetic load
  Genetic load
  In population genetics, genetic load or genetic burden is a measure of the cost of lost alleles due to selection or mutation...
  
  , which over time will result in extinction.

• A Vortex: The A vortex is a result of an increase in genetic drift and a corresponding decrease in genetic variance
  Variance
  In probability theory and statistics, the variance is a measure of how far a set of numbers is spread out. It is one of several descriptors of a probability distribution, describing how far the numbers lie from the mean . In particular, the variance is one of the moments of a distribution...
  
   which leads to a decrease in "population adaptive potential", and eventual extinction. This vortex can result from biological invasion
  Invasive species
  "Invasive species", or invasive exotics, is a nomenclature term and categorization phrase used for flora and fauna, and for specific restoration-preservation processes in native habitats, with several definitions....
  
  , resulting in large scale hybridization and outbreeding depression.