6.17 Extinction

What extinction means

Extinctions have happened throughout the history of life. The fossil record shows that most species that have ever lived are now extinct.

Causes of extinction

• New predators: for example, when humans brought rats, cats and pigs to islands such as Mauritius, they ate the eggs of the dodo, which could not fly.
• New diseases: a species may have no resistance to a new pathogen.
• Competition: a new, more successful species may outcompete it for food or space, for example grey squirrels outcompeting red squirrels in much of the UK.
• Catastrophic events: volcanic eruptions, or an asteroid collision, which is thought to have caused the extinction of the dinosaurs 66 million years ago.
• Changes to the environment over geological time, such as climate change; today, human activity such as deforestation and pollution destroys habitats faster than species can adapt.

Why some species are at greater risk

Species are more likely to become extinct if they:

• have a small population or live in only one place
• reproduce slowly
• cannot adapt quickly enough to the change, because there is too little variation for natural selection to act on.