14.1 Essential ideas

14.1.4 Conservation of biodiversity

Biodiversity is a measure of the richness and evenness of an ecological community, where:

  • species richness is the total number of different species, and organism richness is the total number of individuals of each species
  • evenness is the relative abundance of different species.

Conservation biologists must consider both factors when attempting to preserve ecosystems.

Measuring biodiversity

It is usually impossible for scientists to make direct counts of species number and relative abundance, so sampling techniques are used to measure populations.

For example, the following data was collected from a quadrat sample of two different communities.

Species Number of individuals sampled at community 1 Number of individuals sampled at community 2
Daisy 260 16
Dandelion 457 910
Buttercup 283 74
Total individuals 1000 1000

Both communities have the same richness (same number of species and same number of individuals) but community 2 is dominated by one species. Community 1 has more evenness, and as a result, has higher overall biodiversity.

A common measurement of the biodiversity of a community is called the Simpson’s reciprocal index of diversity. It can be calculated using this formula:

D equals fraction numerator left parenthesis N minus 1 right parenthesis over denominator capital sigma n left parenthesis n minus 1 right parenthesis end fraction

D = diversity index, N = total number of organisms of all species found, and n = number of individuals of a particular species

In this calculation, both richness (numerator) and evenness (denominator) are taken into account to give a complete picture of biodiversity.

The lowest possible value for a Simpson’s reciprocal index is 1, which corresponds to a community with no biodiversity (for example, a community made of a single population of one species). As the reciprocal index of diversity increases, richness and evenness also increase.


Use the data from the table above to calculate the Simpson’s reciprocal indices for both communities. Show your working.

Conservation methodologies

  • Ex situ conservation involves preserving species outside natural habitats. This could involve captive breeding programmes in zoos or propagation of plants in botanical gardens.
  • In situ conservation involves monitoring and actively managing populations in natural habitats, especially nature reserves and parks. This could involve culling invasive predators, feeding animals, or re-introducing species that have been overfished or hunted.
  • Biogeographical factors, such as the heterogeneity of terrain, and the exposure to ‘edge effects’, influence species diversity.
  • Large, uninterrupted nature reserves are best for species preservation. 

biogeographicalFigure 14.1.4a – How biogeographical factors affect biodiversity is considered in the design of nature parks

Indicator species

  • Certain species are more sensitive to changes in the environment than others. They have narrower limits of tolerance for various abiotic factors.
  • Species that are used to monitor the conditions of limiting factors of an ecosystem are known as indicator species.
  • Some common indicator species are small crustaceans (e.g. mussels and shrimps), insects (e.g. dragonflies) and most amphibians (because their skin is permeable to many toxins, including heavy metals).

lichensFigure 14.1.4b – Lichens are species that indicate relative concentrations of sulphur dioxide in the air

  • When an indicator species’ limits of tolerance are known, ecologists can create a biotic index. Using a biotic index, pollution levels are indicated by the presence or absence of different species in the habitat.

biotic index freshwater pollutionFigure 14.1.4c – A simplified biotic index for freshwater pollution

Essential idea

Entire communities need to be conserved in order to preserve biodiversity.

Course link

Review how to perform a quadrat sample: 4.2.2 Chi-square statistics and quadrat sampling


Is random sampling a useful tool for scientists despite the potential for sampling bias?

Language tool

In some resources, Simpson’s reciprocal index of diversity is called ‘Simpson’s index’ or ‘Simpson’s index of diversity’, even though those two terms refer to specific parts of the complete calculation. Don’t let the nomenclature confuse you – just make sure you are using the right formula!

Nature of Science

Scientists collaborate with government agencies and non-government organisations in the preservation of species.

captive breeding14.1.4d – Captive breeding
The goal of ex situ captive breeding programmes is to replenish natural populations. Eventually, this tiger should be ready for re-introduction to its natural habitat.

Science and social responsibility (Aim 8)

Supported by governments or large non-government grants, scientists devote a large amount of effort to saving particular animal species, especially large mammals, through captive breeding programmes. What criteria should be used to justify a hierarchy of value for one species over another?

wildlife corridorFigure 14.1.4e – Wildlife corridor
Wildlife corridors are in place in many natural parks in the world. This one is in Banff National Park, Canada.

Key concept

Most endangered species are at risk because of loss of habitat. They are adapted to living in deep forest conditions, and when their habitat is fragmented, the distribution of species is confined to smaller interior areas. This phenomenon is an example of the ‘edge effect’.

edge effectFigure 14.1.4f – Edge effects