AQA AS Level Biology Unit 2 - Biodiversity

species diversity topic in aqa as unit 2 bio

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Biodiversity is the general term used to describe variety in the living world. It refers to the number and variety of living organisms in a particular area and has 3 components:

  • Species diversity - refers to the number of different species and the number of individuals of each species within any one community
  • Genetic divesity - refers to the variety of genes possessed by the individuals that make up any one species.
  • Ecosystem diversity -refers to the range of different habitats within a particular area

One measure of biodiversity is species diversity. It has 2 components:

  • the number of different species in a given area
  • the proportion of the community that is made up of an individual species
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Measuring species diversity

One way of measuring species diversity is to use an index that is calculated as follows:


D = species diversity index

N = total number of organisms of all species

n = total number of organisms of each species

( = sum of

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Species diversity and ecosystems

Biodiversity reflects how well an ecosystem functions.The higher the species diversity index the more stable an ecosystem ususally is and the less effected by climate change.

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Impact of agriculture

  • controlled by humans
  • farmers select species to populate in an area
  • number of species and genetic variety of alleles is reduced
  • any particular area can only support a certain amount of biomass
  • other species have to compete for little space and resources
  • pesticides are used to  exclude competitive species
  • overall effect is reduction in species diversity
  • species diversity is low in agricultural ecosystems
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Impact of deforestation

  • human intervention
  • many different species have habitats between the layers of the rainforest
  • tropical rainforests have the highest species diversity of any ecosystem
  • deforestation is the permanent destroying of forests and conversion of the land
  • loss of biodiversity
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