Populations in ecosystems

• Describe the method to mark release recapture

  -Capture a 1st sample and mark them in a way that is non-toxic and doesn’t increase their chance of predation

  -Release the sample and allow time for them to randomly redistribute

  -Capture a 2nd sample and count the number marked

  -Population size = number in 1st sample x number in 2nd sample / number marked in 2nd sample
• What assumptions are made when carrying out mark release recapture?

  -Marking is non-toxic and doesn’t increase their chance of predation

  -Enough time was left to allow organisms to randomly redistribute

  -No migration between other populations

  -No births or deaths
• Define carrying capacity (k)

  The maximum size of a population of a species that an ecosystem can support
• Why does the carrying capacity for a species vary between ecosystems?

  -The effect of abiotic factors

  -Interactions between organisms:

  • Intraspecific competition (between same species)
  • Interspecific competition (between different species)
  • Predation
• What are turbidity measurements used for?

  To investigate the growth rate of a broth culture of microorganisms
• Describe how to measure turbidity

  At regular intervals, the light absorbance of a sample of microorganisms is tested with a colourimeter and plotted on a calibration curve. The higher the light absorbance, the higher the turbidity, and the higher the number of microorganisms
• What is meant by dynamic?

  Ecosystems are constantly changing
• Describe the primary succession stages

  -A named pioneer species colonises a hostile abiotic environment

  -The pioneer species changes the habitat by forming soil and humus

  -This makes the abiotic environment less hostile for other species

  -Other named species can colonise so biodiversity increases

  -The environment may then become less suitable for previous species

  -A stable named climax community is reached
• What are the features of a climax community?

  -The same species are present over a long period of time

  -Population sizes are stable

  -Abiotic factors are stable over a long period of time
• Explain conservation in relation to succession

  Conservation of habitats can involve management of succession if the species being conserved is easily outcompeted
• What are ways to manage succession?

  -Grazing by livestock

  -Coppicing

  -Mowing

  -Burning
• What are some conservation methods?

  -Keeping seed banks of different species in case of species loss

  -Captive breeding for endangered species

  -Fishing quotas

  -Establishing protected areas free of human interference
• Describe how to use random sampling with quadrats

  -Create a grid with tape measures and use a random number generator to find coordinates

  -Place a frame quadrat at each coordinate and record the number of species that appear

  -Use more than 20 coordinates for a representative sample

  -Calculate a mean and a statistical test

  -Population size = Area of field/Area of quadrat x Mean of the sample
• Describe how to use a belt transect

  -Lay a rope or tape measure down and mark at regular intervals

  -Place a frame quadrat at each interval

  -Use multiple belt transects

  -Count the number of species that appear or calculate percentage cover
• What does the null hypothesis state in a chi squared test?

  There is no significant difference between the observed and expected results
• How is the chi squared value obtained?

  ((Observed-Expected^2)/Expected)
• How are the degrees of freedom calculated in a chi squared test?

  Number of groups - 1
• What does the null hypothesis state in a T-test?

  No significant difference between the means of the two groups
• How are the degrees of freedom calculated in a T-test?

  (Number in sample 1 + number in sample 2) -2
• How is a value for t obtained in a T-test?

  (Mean 1 - mean 2) / √(Standard deviation 1^2/Number of values in 1) + (Standard deviation 2^2/Number of values in 2)
• What does the null hypothesis state in a Spearman's rank test?

  There is no correlation between variable 1 and variable 2
• How are the degrees of freedom calculated for Spearman's rank?

  N-2