A-LEVEL BIOLOGY OCR NOTES 
biodiversity

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Biodiversity
  • Biodiversity is the variety of organisms in an area. It can be considered on different levels including habitat, species and genetic diversity of an area
  • Habitat diversity refers to the range of habitats present in a region
  • Species diversity is the number of species and the number of individuals within each species in a specified area. It takes into account species richness and species evenness.
  • Species richness is a measure of the number of different species in a community.
  • Species evenness is a measure of the relative abundances of different species in an area.
  • Genetic diversity is the variety of all the genes (number of different alleles of genes) possessed by the individuals in a population or whole species
  • Alleles are different forms of the same gene
  • The greater the genetic diversity, the greater the ability of the species to adapt to a changing environment.
  • Genetic diversity can be estimated by comparing physical characteristics or by analysing genomes.
  • Species with a greater number of polymorphic genes tend to have greater genetic diversity
  • Simpson’s diversity index (D) measure biodiversity taking into account species richness and evenness
  • N = total number of organisms of all species
  • n = total number of organisms of each species
  • Factors affecting biodiversity include:
    • Human population growth increases the demand for resources from the environment
    • Agriculture reduces biodiversity by monoculture, use of herbicide & pesticides, hedgerow removal and woodland clearance
    • Climate change is causing animals to migrate or die
  • Reasons for maintaining biodiversity can be:
    • Ecological- ecosystems are more stable when biodiversity is high. Keystone species are a species which has a disproportionate effect on its environment relative to its abundance, their removal will greatly reduce the ability of an ecosystem to function
    • Economical- provides resources
    • Aesthetic
    • Ethical
  • Conservationists protect biodiversity with methods such as: giving endangered species legal protection, creating protected area & The Environmental Stewardship Scheme.
  • A balance between conservation and agriculture is needed