Extinction

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Extinction: The death of the last surviving individual of a species, population, or gene, locally or globally.

The number of extinctions per year per species or to make numbers more reasonable per million species per year. (MSY) The extinction rate that is normal according to the fossil record is called background extinction or 1 E/MSY

Mass extinctions - A sharp increase in the rate of extinction there has been at least 5 mass extinctions last one was 65m

Nearly 70% of all species ever existed on this planet have gone.

Catastrophic extinctions - Asteroid, acid rain, cosmic radiation, disease and radiation and changes sea levels.

Planed extinctions to be helpful to humans e.g. small pox.

SMALL POPULATION SIZE MAKES A SPECIES MOST SUSCEPTIBLE TO EXTINCTION the rarer the species the more at risk.

N= number of individuals

Ne = effective population size

natural causes of rarity:

Specialization

small geographic range (endemic species)

Sparse population within range

Large body size

Top predators are always rarer

Chance events lead to isolation

Genetic bottleneck

Loss of genetic diversity

What problems arise with small population size:

Genetic Drift and inbreeding.

Inbreeding often results in reduced fitness, birth weight and fertility.

Expression of deletrious alleles

Leads to the Extinction Vortex

Small population leads to inbreeding and random genetic drift and loss of genetic variability which leads to reduction in individual fitness and population adaptability and lower reproduction.