Extinction

Noadswood Science, 2012

Extinction• To understand why a species may become extinct

Tuesday, April 18, 2023

Extinction• Time periods in the history of life on Earth during which

exceptionally large numbers of species go extinct are called mass extinctions – these extinctions are quite different from the rate of extinction, which occurs even when the diversity of life is increasing

• Many species vanished in five cataclysmic mass extinctions and today, 99.9 percent of all species that have existed on Earth are extinct: -▫ The Ordovician-Silurian extinction – 439 million years ago▫ The Late Devonian extinction – 364 million years ago▫ The Permian-Triassic extinction – 251 million years ago▫ The End Triassic extinction – 200 million years ago▫ The Cretaceous-Tertiary extinction – 65 million years ago

Extinction• Individuals that are poorly adapted to their environment

are less likely to survive and reproduce than those that are well adapted

• Similarly, it is possible that a species that is poorly adapted to its environment will not survive and will become extinct

• Extinction is the permanent loss of all members of a species from the face of the Earth

• Species become extinct if they cannot adapt to a change in the environment or to the arrival of other organisms

General Causes Of Extinction• Some of the factors which lead to the extinction of a species

can include: -▫ Changes to the environment, such as a change in climate ▫ New diseases ▫ New predators ▫ New competitors

Extinction & Fossils• The fossil record shows that many species have become

extinct since life on Earth began (more than 99.9% of species to have ever lived are now extinct)

• Extinction is still happening and a lot of it occurs because of human activities – we compete with other living things for space, food and water, and we are very successful predators – we could well be the cause of the sixth great mass extinction

Extinction Examples – Dodo• The dodo was a large flightless bird that lived on Mauritius,

an island in the Indian Ocean

• The island was uninhabited and the dodo had no natural predators until Mauritius was colonised by the Dutch in 1638

• Dodos were hunted for food and easy to catch because they were not afraid of people – new competitors were brought onto the island, including pigs, cats and rats, which ate the dodos' eggs and their young…

• Within 80 years, the dodo was extinct

Extinction Examples – Tasmanian Wolf• The Tasmanian Wolf is believed to have been extinct for

nearly sixty-five years – it was hunted until almost extinction and the remaining few died from disease

• The last few remaining animals were put into captivity to try to save them, but this failed

Red Squirrel Extinction• Complete the red squirrel

extinction worksheet

Red Squirrels• Red squirrel populations have greatly fluctuated - very low in

the 17th and 18th centuries but reaching such high levels in the early 20th century that it was considered a pest in some areas

• Massive replanting of woodland occurred in the 19th century, but between 1876 and 1929 there were several introductions of the North American grey squirrel into Britain – when their numbers have increased, the red squirrel numbers have significantly decreased

• Grey squirrels have replaced red squirrels in many areas of Britain because grey squirrels carry diseases which are fatal to red squirrels and they are able to digest seeds from broadleaf woodlands better than the red squirrels

Red Squirrels• Where the coniferous woodland remains in Britain the

population is most stable for the red squirrels

• To stop red squirrels from becoming extinct the grey squirrels need to be killed, reducing the threat of disease and competition to the red squirrel

• To increase the red squirrel populations the forest needs to be managed, ensuring the red squirrels have enough food and shelter, and limiting the prey which may predate them

The Red List• The IUCN species programme - assessing the conservation

status of species, subspecies, varieties, and even selected subpopulations on a global scale in order to highlight taxa threatened with extinction, and therefore promote their conservation

www.iucnredlist.org

Dinosaurs & Mammals• Why is it that cataclysmic event which caused the dinosaurs to

become extinct did not also cause the extinction of mammals (which were also around at the time)?

Dinosaurs & Mammals• Most scientists believe large scale climate change was the

cause of the dinosaur extinction – possibly caused by a giant meteorite crashing into the Earth

• As the environment changed the dinosaurs were unable to adapt, and died out

• As the Earth finally began to warm up again mammals, which are able to regulate their own body temperature, became dominant

Extinction• Complete the extinction worksheet

Extinction

Extinction