This is a measure of the number of different organisms in a habitat. Across the planet levels of biodiversity are reducing because of human interference.

Measuring Biodiversity

Specification Reference

"Know that biodiversity can be assessed at different scales: (a) within a habitat at the species level using a formula to calculate an index of diversity; (b) within a species at the genetic level by looking at the variety of alleles in the gene pool of a population."
This is the variety of organisms living in a habitat.

Variation in a Habitat

  • Species richness - the number of different species within a community. This does not account for the number of each.
  • Species diversity - takes into account the number of individuals of each species. An index can be found using the following formula:
  • D = [N(N-1)] / [Σn(n-1)]
  • N = number of all organisms of all species
  • n = number of individuals of each species
The larger the index, the greater the diversity.

Variation in a Species

Within a species all organisms have the same gene pool. However, each organism may have a different combination of alleles. This results in genetic diversity.

Understanding biodiversity allows conservation efforts to be well informed and effective.

Why Maintain Biodiversity?

Specification Reference

"Understand the ethical and economic reasons (ecosystem services) for the maintenance of biodiversity."
There are a number of reasons why levels of biodiversity should be increased or maintained. Reasons include:
  • More stable populations
  • More resilient populations (more alleles allows populations to adapt more easily)
  • Loss of keystone species could have severe negative impacts
  • Pleasant to look at
  • Ecotourism opportunities
  • Provide goods and sources of medicine
  • Stabilise soils
  • Increase the gene pool further increasing the ability of a population to adapt


Specification Reference

"Understand the principles of ex-situ (zoos and seed banks) and in-situ conservation (protected habitats), and the issues surrounding each method."
This is to preserve something, keeping it in its natural state.

In-Situ Conservation

This is conservation within the natural environment. Methods can include restoration and legislation.

Advantages Disadvantages
Protects more than one species Hard to enforce any legislation
Inexpensive Some areas need extensive work
Fewer facilities required Populations may still decline
Can conserve unknown species

Ex-Situ Conservation

This is the conservation of plants and animals outside of their natural habitat (zoos and seed banks).

Advantages Disadvantages
Eliminates predators Very expensive
Prevents poaching Cannot fully recreate a natural habitat
Require less space Disease can quickly spread
Inter-zoo exchange maintains genetic diversity


These are an example of ex-situ conservation. Animals are placed into an artificial habitat and usually enter a captive breeding programme.

There has been limited success so far and many feel it is unfair to keep animals in captivity.

Advantages Disadvantages
Educate the public When reintroduced into the wild animals can lack survival skills
Zoos can carry out research Limited success seen so far
Increase population numbers


These play a major role in storing and conserving genetic diversity. Seeds are stored in dry, cold conditions to keep the seeds viable. The process of seed collection is outlined below:
  1. Seeds collected
  2. Tested for viability
  3. Cleaned & sterilised
  4. Stored
  5. Routinely checked for viability
  6. If required seeds will be replaced
This allows for future repopulation if necessary.