4.6 Biodiversity within a community

• What is biodiversity?

  • ● Variety of living organisms (species, genetic and ecosystem diversity)
  • ● 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

  • ● Also takes into account number of individuals in each species
  • ● So takes into account that some species may be present in small or high numbers
• What is the formula for index of diversity?

  d = N(N-1)/Σn(n-1)

  N = total number of organisms of all species

  n = total number of organisms of each species, Σ = the sum of

  
• List the steps involved in calculating an index of diversity

  1. Calculate the total number of organisms (N), if not given
  2. Multiply N by (N - 1)
  3. For each species, multiply the number of organisms (n) by (n - 1)
  4. Add up all the values of n(n - 1) to get Σn(n - 1)
  5. Divide N(N - 1) by Σn(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
• Index of diversity: worked example

  1. N for for both habitats - 50
  2. N(N - 1) = 50 x 49 = 2450
  3. n(n - 1) shown in additional columns of table
  4. Σn(n - 1) for habitat X = 450 and for habitat Y = 1300
  5. Habitat X = 2450 / 450 = 5.44, Habitat Y = 2450 / 1300 = 1.88

  
• Explain how some farming techniques reduce biodiversity

  • Removal of woodland and hedgerows
  • Monoculture (growing one type of crop)
  • Use of herbicides to kill weeds
  • Explanation for these 3 techniques:
  • Reduces variety of plants
  • So fewer habitats and niches
  • And less variety of food sources
  • Use of pesticides to kill pests
  • 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
  • ○ Eg. 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 type of crop)
  • ● Reduce use of pesticides
  • ● Growing different crops in the same area (intercropping)
  • ● Using crop rotation of nitrogen fixing crops instead of fertilisers