What Causes Species Extinction?

Species extinction happens when the last living member of a species dies. A species can become extinct if conditions change and its members cannot survive and reproduce quickly enough to maintain the population.

What can cause it?

• Environmental change: A change in temperature or water availability can make a habitat unsuitable. For example, a long drought may kill the plants an animal depends on for food.
• New predators or diseases: A new predator may kill individuals faster than they can reproduce. A new pathogen, which is a microorganism that causes disease, can also reduce a population.
• Competition: Another species may compete more successfully for limited food or space, leaving too few individuals to breed.
• Human activity: Destroying habitats through building or farming leaves less space for other species. Pollution can kill organisms and reduce biodiversity, the variety of species in an area.

These causes can act together. If drought reduces a plant population, animals that eat the plants may have less food. Their numbers could fall too. Extinction is the outcome only if no individuals of the species remain anywhere, not simply because its population has become small in one habitat.

For an exam answer, link the cause to its effect: explain how it reduces survival or reproduction, then how the population could eventually disappear. A common mistake is to say that an individual animal evolves to cope with a change. Natural selection acts over generations: individuals with helpful inherited characteristics are more likely to survive and pass them on. If the species cannot adapt or survive the change, it may become extinct.

This explanation is for separate AQA GCSE Biology, assuming Higher tier; the extinction points also apply at Foundation tier.