Chapter 11

• Define biodiversity

  variety of life in an area which can be measured in terms of genetic, species or habitat diversity
• What is measured in genetic diversity?

  an estimate of gene variants (alleles) in a species
• What is measured in species diversity?

  species richness & species evenness
• What is measured in habitat/ ecosystem diversity?

  • number of different habitats in an area
  • hardest measure of biodiversity - boundaries of ecosystems are often difficult to determine accurately
• species richness

  the number of species in an area
• species evenness

  number of individuals of each species
• Levels of ecological organization

  1. organism - individual
  2. population - group of organisms of same species
  3. community - collection of populations in habitat
  4. habitat - natural environment of organisms
  5. ecosystem - community of species along w abiotic components
• What does an ecosystem need for it to be considered biodiverse?

  it needs species richness and evenness to both be high
• Principles to bear in mind when designing sampling method

  • larger sample sizes - more representative of whole ecosystem
  • avoiding bias will increase validity of results
  • sampling can only be claimed to represent a close estimate of biodiversity
• Random sampling

  decide location of sampling points by:

  • generating random numbers which are used as grid coordinates
  • taking samples from these coordinates
• Advantages of random sampling

  avoids bias
• Disadvantages of random sampling

  • can be unrepresentative of whole ecosystem - especially if area is large
  • some species may be unevenly distributed & found only in certain parts of ecosystem - these could be missed
• 2 types of non-random sampling

  • stratified
  • systematic
• Stratified sampling

  study site divided into smaller areas, based on distribution of habitats
• Advantages of stratified sampling

  • ensures species are not overlooked
  • more representative of the ecosystem
  • reduces sampling error
• Systematic sampling

  • A transect is used where environmental gradients exist (e.g. soil pH/ light intensity changes across a habitat
  • can investigate whether the distribution of organisms also changes across the habitat
• Line transect 


  involves identifying presence of a species at set points along a line (usually marked w tape)
• Belt transects

  • more detailed
  • abundance of species can be estimated (e.g. by using quadrats)
• Pooter

  • samples insects
  • insects are sucked into a chamber
• Sweep nets

  • samples insects in long grass
  • net swept through the habitat
• Pitfall traps

  • samples small, crawling invertebrates
  • hole in ground traps organisms
• Kick sampling

  • samples river-dwelling organisms
  • river bed is disturbed and organisms are captured in a net
• What is used to sample plants?

  quadrats
• Point quadrat

  • pins are pushed through holes in a bar that spans the quadrat
  • all species that touch pins are identified & recorded

  
• Frame quadrat

  • quadrat divided into grid of smaller squares
  • species identified and their abundance can be estimated
• What is needed to measure species richness?

  an identification key
• How do you measure species evenness?

  • use method for measuring abundance
  • e.g. use a quadrat
• 2 ways quadrat can record species abundance

  • count absolute number of individuals (i.e. density per m2)
  • estimate percentage of a quadrat covered by a species
• Why might the percentage cover of a species be recorded rather than its density?

  • time limitations
  • cases where individuals of a species are difficult to count
• Simpson's diversity index

  $D=$$1-(∑(n/n)²$

  • n = number of individuals of a species
  • N = total number of all individuals of all species
• What does high/low value of Simpson's index reflect?

  • high = high biodiversity
  • low = ecosystem dominated by few species & is unstable
• What are alleles?

  different versions of the same gene (i.e. gene variants)
• Which factors increase genetic diversity?

  • DNA mutation
  • breeding between populations of the same species
• Factors that decrease genetic diversity

  • selective breeding
  • captive breeding
  • genetic bottlenecks (when population reduced to small size due to disease, habitat destruction or migration)
• What does it mean if a species has a low/high genetic diversity?

  • low = very few gene variants
  • high = contains a wide range of gene variants - increases chance of species adapting & surviving to environmental changes
• Methods to calculate biodiversity

  • number of alleles per gene
  • heterozygosity - proportion of individuals in a population that have 2 diff alleles for a particular gene
  • proportion or genes for which more than one allele exists - polymorphic genes
• Polymorphic gene

  gene that has 2 or more possible alleles
• How to calculate proportion of polymorphic genes

  = number of polymorphic genes/ total number of genes
• 3 factors affecting biodiversity

  • human population growth
  • agriculture
  • climate change
• How does population growth affect biodiversity?

  • deforestation - destroyed habitats cause animal migration or death