3.4.6 Biodiversity within a community

Define biodiversity. (2 marks)

- The variety of living organisms, including species, genetic, and ecosystem diversity.

- Can relate to habitats ranging from small local areas to the whole Earth.

Define a community and species richness. (2 marks)

- A community is all populations of different species living in the same area.

- Species richness is a measure of the number of different species in a community.

Describe what an index of diversity does. (2 marks)

Shows the relationship between the number of species in a community and the number of individuals in each species.

Explain why index of diversity is more useful than species richness. (2 marks)

- Takes into account the number of individuals in each species.

- Considers that some species may be present in small or high numbers.

State the formula for index of diversity. (2 marks)

where N is the total number of organisms of all species and n is the total number of organisms of each species.

Describe the steps involved in calculating an index of diversity. (5 marks)

- Calculate the total number of organisms (N) if not given.

- Multiply N by (N - 1).

- For each species, multiply the number of organisms (n) by (n - 1).

- Add all values of n(n - 1) to get Σn(n - 1).

- Divide N(N - 1) by Σn(n - 1).

Describe how index of diversity values can be interpreted. (2 marks)

- A high value means many species are present and species are evenly represented.

- A low value means the habitat is dominated by one or a few species.

Explain how some farming techniques reduce biodiversity. (4 marks)

- Removal of woodland and hedgerows reduces variety of plant species, so there are fewer habitats and niches and less variety of food sources.

- Monoculture reduces the variety of plant species and therefore habitats and niches.

- Use of herbicides to kill weeds reduces plant diversity and food sources.

- Use of pesticides to kill pests reduces predator populations.

Explain the balance between conservation and farming. (3 marks)

- Conservation is required to increase biodiversity.

- When implemented on farms, yields can be reduced, lowering profit or income for farmers.

- Financial incentives or grants are offered to offset losses.

State examples of how biodiversity can be increased in areas of agriculture. (4 marks)

- Reintroducing field margins and hedgerows.

- Reducing the use of pesticides.

- Growing different crops in the same area.

- Using crop rotation with nitrogen-fixing crops instead of fertilisers.

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