AS-LEVEL AQA BIOLOGY NOTES 
TOPIC 6: biodiversity within a community

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Biodiversity
  • The variety of living species
  • The degree of nature’s variety
  • It allows for the permanent stability of an ecosystem
  • Involves an equilibrium between species

Biodiversity can be considered at different levels.
Habitat
  • Range of habitats
  • Each may be occupied by different species
  • Diverse habitats may lead to diverse species
  • It is essential to conserve these
Species
  • Difference between species
  • This could be within a habitat, or a community
  • Differences could be structural or physical
  • We can collect data about different species
    • This will inform species richness
Genetic
  • Genetic variation exists within a species
  • Degree of allelic variation between the members of a species
  • It is good
    • Lack of variation results in a lack of ability to adapt
    • Natural selection depends on variation


Species Richness
  • This is the number of different species present in a habitat
  • The more species present, the richer the habitat
  • Observe and record the species present in a habitat
  • Samples should be taken
  • Visual surveys should be taken, to ensure that nothing is missed
  • However, this does not take into account the number of individuals of each species
  • Not sufficient data to measure diversity alone

Diversity Index
  • Diversity index is a better way of describing biodiversity
  • It takes into account both species richness and evenness
  • Gives an idea of the number of each species relative to population size
  • Small and large populations are treated differently
  • The formula is:
D = N(N-1)n(n-1)
Where n = total number of organisms in each species
And N = the total number of organisms of all species


High Index of Biodiversity means…
  • Indicates a diverse habitat
  • Many different species live there
  • Small change to environment may only affect one species
  • If this species is only small population, then only a small proportion of the habitat is effected
  • Total effect on the habitat would be small
  • Tends to be stable habitat
Low Index of Biodiversity means...
  • Suggests it is dominated by few species
  • Small change to the environment may affect one of the major species
  • Could damage or destroy the whole species
  • Small change would have a very large impact on the environment
  • Much less stable environment

Benefits of having large biodiversity
  • Extinction reduces biodiversity
  • Human clearing of land fro agriculture removes habitats
  • This increases chances fo extinction
  • Modern farming often plants only one type of crop (monoculture)
  • Makes harvesting easier
  • However, this has a very low diversity and reduces the variation of animals in this habitat
  • Selective breeding is also used in agriculture, leading to genetic erosion
  • Genetic erosion reduces genetic diversity
  • Prevents organisms from adapting to survive changes in their environment

Modern farming and biodiversity
  • Deforestation = clearing forests for agriculture or buildings
  • Reduces biodiversity
    • Loss of habitat
    • Destruction of species
    • Change in microclimate
    • Animals move away to habitats they are worse adapted to
    • Disruption of complex food webs

Conservation of forests is sustainable
  • Deforestation creates space of agriculture but the land becomes infertile after a few years
  • Cattle farming is not economically rewarding
  • Conservation can generate income from eco-tourism
  • The forests are a natural source of e.g. fruit, rubber
  • Preservation of gene pools that come from conservation mean wild alleles are available to use in genetic engineering or selective breeding
  • Tropical rainforests should be conserved to avoid:
    • Loss in species and genetic diversity
    • Disruption of food chains
    • Loss of potential medicines
    • Loss of wood/timber
    • CO2 build-up in atmosphere contributing to global warming
    • Leaching of ions in the soil
    • Soil erosion