Extinctions

What is Extinction? Extinction occurs when the last existing member of a given species dies – In other words…there aren’t any more left! It is a scientific certainty when there are not any surviving individuals left to reproduce Functional Extinction – Only a handful of individuals are left – Odds of reproduction are slim

Extinction Local, ecological and true extinction The ultimate fate of all species just as death is for all individual organisms 99.9% of all the species that have ever existed are now extinct – To a very close approximation, all species are extinct Background vs. Mass Extinction – Low rate vs % of total – Five great mass extinctions in which numerous new species (including mammals) evolved to fill new or vacated niches in changed environments – 10 million years or more for adaptive radiations to rebuild biological diversity following a mass extinction Extinctions open up new opportunities for speciation and adaptive radiation..BUT you can have too much of a good thing!

Causes of Extinction Genetics and Demographics – Small populations = increased risk – Mutations Causes a flux in natural selection Beneficial genetic traits are overruled – Loss of Genetic Diversity Shallow gene pools promote massive inbreeding and low genetic variations results in extinctions.

Extinctions Habitat Disruption – Volcanic Eruptions – Asteroid Impacts – Sea Level Change Habitat Modification – Climate Change – Mountain-Building – Sea Level Change – Precipitation Change – Toxic Materials “Exotic” Species Introductions – Continental Drift

Causes Con’t. Predation – Competition – Disease Coextinction Mass Extinction Planned Extinction

Coextinction The loss of one species leads to the loss of another Chain of extinction Can be caused by small impacts in the beginning A predator looses its food source Affected by interconnectedness in nature

Mass Extinction Aka: an extinction event A sharp decrease in the number of species on Earth in a short period of time Coincides with a sharp drop in speciation – The process by which new biological species arise There have been at least 5 – Last one was 65M years ago

Mass Extinctions 1.Cretaceous-Tertiary Extinction (65). 2.End Triassic Extinction (200). 3.Permian Triassic Extinction (250). 4.Late Devonian Extinction (364). 5.Ordovician-Silurian Extinction (440). (#= millions of years ago)

Extinction in the Context of Evolution If – the environment changes rapidly and – The species living in these environments do not already possess genes which enable survival in the face of such change and – Random mutations do not accumulate quickly enough then, All members of the unlucky species may die