Biology AQA new AS level unit 2, biodiversity.


Species Diversity.

Biodiversity - term used to describe variety in living world. Refers to number & variety of of living organisms in a particular area & has 3 components:

  • 1. Species Diversity - number of different species & number of individuals of each species within any 1 community.
  • 2. Genetic Diversity - variety of genes possessed by individuals that make up a species.
  • 3. Ecosystem Diversity - range of different habitats within a particular area.

Species diversity is a measure of biodiversity and has 2 components: number of different species in a given area & proportion of the community that is made up of an individual species. 2 communities may have same number of species but the proportion is different.

Species diversity (d) = N(N-1)/sum of n(n-1)

where N = total number of orgs of all species & n = total number of orgs of each species.

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Ecosystem - all the living and non-living components of a particular area.

  • Biodiversity reflects how well an ecosystem functions.
  • The higher the species diversity index, the more stable an ecosystem is and the less it is affected by climate change.
  • In extreme conditions only a few species have the necessary adaptations to survive the harsh conditions so the species diversity index is usually low - communities are dominated by climatic factors, not the organisms.
  • In less hostile environments the species diversity index is normally high resulting in a stable ecosystem dominated by living organisms.
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Impact of Agriculture.

  • As ecosystems develop they become complex communities with many individuals and species.
  • Agricultural ecosystems are controlled by humans so are different.
  • The number of species and the genetic variety of alleles is to reduced to the few that exhibit the desirable features.
  • To be economic there need to be a large number with these features.
  • Any particular area can only support a certain amount of biomass, if most of the area is taken up by species the farmer wants then there is a smaller area for other species.
  • Species have to compete for the leftover space and resources.
  • Pesticides exclude certain species that compete for light, mineral ions, water and food required by the farmer.
  • Overall, reduction in species diversity so index is low.
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Impact of Deforestation.

  • Forests form many layers so there are lots of habitats available and so species diversity is high.
  • Deforestation mostly due to deliberate human action.
  • Deforestation - permanent clearing of forests and the conversion of land to other uses e.g. agriculture.
  • Some forests are destroyed by man-made pollutants e.g. acid rain.
  • Deforestation leads to loss of biodiversity.
  • TRFs account for half of all the earth's species but cover only 7%.
  • Replacement has reduced species diversity.
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Zoe Alford


great notes :)

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