Extinction Vortex

TYPES OF VORTEX

R Vortex: The R vortex is initiated when there is a disturbance which facilitates a lowering of Population size (N) and a corresponding increase in Variability (Var(r)). This event can make populations vulnurable to additional disturbances which will lead to an additionally decreased value for N and an increased value for Var(r). A prime example of this would be the disruption of Sex Ratios in a population away from 50:50.

D Vortex: The D vortex is initiated when N decreases and Var(r) increases such that the spatial distribution (D) of the population is increased and the population becomes 'patchy' or Fragmented . Within these fragments local extinction rates increase which, through Positive Feedback , further increases D.

F Vortex: The F vortex is initiated by a decrease in N which leads to an increase in Heterozygosity and genetic drift, which results in increased degrees of inbreeding depression and an increase in population Genetic Load , 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 which leads to a decrease in ''population adaptive potential'', and eventual extinction. This vortex can result from Biological Invasion , resulting in large scale Hybridization and outbreeding depression.

REFERENCE

Gilpin, M. E. and Soulé, M. E., (1986). "Minimum Viable Populations: Processes of Species Extinction." pp. 19-34 in M. E. Soulé, ed. ''Conservation Biology: The Science of Scarcity and Diversity.'' Sinauer, Sunderland, Mass.

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Extinction Vortex