AQA A Level Biology

Revision Notes

4.6.1 Biodiversity Within a Community


  • Biodiversity can be thought of as a study of all the variation that exists within and between all forms of life
  • Biodiversity looks at the range and variety of genes, species and habitats within a particular region
  • It can be assessed on different scales
    • The number and range of different ecosystems and habitats on the entire planet
    • The number of species and their relative abundance within a small, local habitat (like a pond)
  • Biodiversity is very important for the resilience of ecosystems, in that it allows them to resist changes in the environment

Ecosystem or habitat diversity

  • This is the range of different ecosystems or habitats within a particular area or region
  • If there is a large number of different habitats within an area, then that area has high biodiversity
    • A good example of this is a coral reef. They are very complex with lots of microhabitats and niches to be exploited
  • If there is only one or two different habitats then an area has low biodiversity
    • Large sandy deserts typically have very low biodiversity as the conditions are basically the same throughout the whole area

Species diversity

  • The mix of different species that exist within a particular area or region can be measured to indicate levels of biodiversity
  • It can be measured in different ways: species richness and species diversity
  • Species richness is the number of species within a community
    • An ecosystem such as a tropical rain forest that has a very high number of different species would be described as species-rich
  • Species diversity looks at the number of different species in a community, and also the evenness of abundance across the different species present
    • The greater the number of species in an ecosystem, and the more evenly distributed the number of organisms is among each species, then the greater the species diversity
    • For example, an ecosystem can have a large number of different species but for some species, there may only be 3 or 4 individuals. As a result, this ecosystem does not necessarily have high species diversity
  • Ecosystems with high species diversity are usually more stable than those with lower species diversity as they are more resilient to environmental changes
    • For example in the Pine forests of Florida, the ecosystem is dominated by one or two tree species. If a pathogen comes along that targets one of the two dominant species of trees, then the whole population could be wiped out and the ecosystem it is a part of could collapse

Maintaining biodiversity

  • There are many different reasons why maintaining biodiversity is beneficial
  • Biodiversity impacts all organisms (including humans) on a global scale

Reasons for maintaining biodiversity table
Summary of Reason for Maintaining Biodiversity Table, downloadable AS & A Level Biology revision notes

Author: Lára

Lára graduated from Oxford University in Biological Sciences and has now been a science tutor working in the UK for several years. Lára has a particular interest in the area of infectious disease and epidemiology, and enjoys creating original educational materials that develop confidence and facilitate learning.

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