Biodiversity within a community

• What is biodiversity?

  • Variety of living organisms
  • Can relate to a range of habitats, from a small local habitat to the earth
• What is a community?

  All populations of different species that live in an area
• What is species richness?

  A measure of the number of different species in a community
• What does an index of diversity do?

  Describes the relationship between:

  1. The number of species in a community (species richness)
  2. The number of individuals in each species (population size)
• Suggest why index of diversity is more useful than species richness:

  • Takes into account number of individuals in each species
  • Takes into account that some species may be present in small or high numbers
• List the steps involved in calculating an index of diversity:

  1. Calculate the total number of organisms (N)
  2. Multiply N by (N-1)
  3. For each species, multiply the number of organisms (n) by (n-1)
  4. Add up the values of (n-1) to get sum of n(n-1)
  5. Divide N(N-1) by sum of n(n-1)
• What is the formula for index of diversity?


  $d=$$N(N-1)/∑n(n-1)$
• Describe how index of diversity values can be interpreted:

  • High = many species present (high species richness) and species evenly represented
  • Low = habitat dominated by one / a few species
• Explain how removal of woodland and hedgerows reduces biodiversity:

  • Reduces variety of plants
  • So fewer habitats and niches
  • And less variety of food sources
• Explain how monocultures reduce biodiversity:

  • Reduces variety of plants
  • So fewer habitats and niches
  • And less variety of food sources
• Describe how use of herbicides to kill weeds reduces biodiversity:

  • Reduces variety of plants
  • So fewer habitats and niches
  • And less variety of food sources
• Describe how pesticides reduce biodiversity:

  Predator population of pest decreases
• Explain the balance between conservation and farming:

  • Conservation required to increase biodiversity
  • But when implemented on farms, yields can be reduced, reducing profit / income for farmers

  -e.g. by reducing land area for crop growth, increasing competition, increasing pest population

  • To offset loss, financial incentives / grants are offered
• Give examples of how biodiversity can be increased in areas of agriculture:

  • Reintroduction of field margins and hedgerows (where farmers only grow one crop)
  • Reduce use of pesticides
  • Growing different crops in the same area (intercropping)
  • Using crop rotation of nitrogen fixing crops instead of fertilisers