Extinction (AQA GCSE Biology): Revision Note

Extinctions

• Extinctions occur when there are no remaining individuals of a species still alive

• Species that are poorly adapted to their environment are less likely to survive and reproduce compared to species that are well adapted to their environment

• If they are unable to survive and reproduce sufficiently to maintain their population numbers they will eventually go extinct

Factors which may contribute to the extinction of a species

• New diseases

  • A species that has previously not had to evolve resistance to a particular disease or pathogen may not have any resistant alleles within its population

  • This will lead to very large numbers of the species dying very quickly and the species may not have time to develop immunity to the new disease before it is wiped out completely

• New predators

  • A species that has previously not had to evolve defence mechanisms (e.g. camouflage, horns, poison etc) to a particular predator will be very vulnerable if the new predator appears

  • This will lead to the species being heavily predated and the species may not have time to adapt (by developing new defence mechanisms) before it is wiped out completely

• New, better adapted and more successful competitors

  • A species will have to compete for resources (e.g. food) if a new competitor species appears that requires the same resources

  • If a new competitor species is better adapted to take advantage of these resources, then it will out-compete the original species

  • This may eventually lead to the original species being wiped out completely

• Changes to the environment over geological time

  • If a change in the environment occurs, a species may not be well adapted to this change and may be wiped out as a result

  • An example of such a change is climate change

  • For example, as global temperatures rise, certain species may not be able to survive at these higher temperatures and may eventually go extinct

• Single catastrophic events

  • Certain events may be catastrophic enough to wipe out entire ecosystems or habitats and therefore the species that live there as well

  • This is especially likely to occur if the species has a limited range (the area where it lives) close to where the event occurs

  • Examples include asteroid collisions with Earth and massive volcanic eruptions