Distribution of organisms

• Temperature can affect the distribution of organisms
• Light intensity can affect the distribution of organisms
• Abiotic Factors

  Non-living factors that can affect the distribution of organisms
• Abiotic Factors

  • Light intensity
  • Soil moisture
  • Temperature
  • pH for soil or pH meter
  • Water
• Biotic Factors

  • Shadow
  • Grazing
  • Light intensity
  • Disease
  • Predation
  • Competition for resources
• pH for soil or pH meter can affect the distribution of organisms
• Probe not left long enough to monitor moisture level
• Soil moisture can affect the distribution of organisms
• Grazing can affect the distribution of organisms
• Water can affect the distribution of organisms
• Shadow can affect the distribution of organisms
• Light intensity can change throughout the day
• Temperature may change throughout the day
• Probe not being left in long enough
• Contamination from previous sample
• Biotic Factors


  Living factors that can affect the distribution of organisms
• Wait for reading to settle
• Take multiple readings at the same time of day
• Clean the probe between each reading
• Thermometer not left long enough
• Wipe the probe between each reading
• A shadow may be cast on the light meter
• Moisture meter should be checked for accuracy
• Light meter should be checked for accuracy
• Thermometer should be checked for accuracy
• pH meter should be checked for accuracy
• Pitfall traps

  1. Can be used to sample small organisms living on the soil surface or in leaf litter

  2. Organisms fall into the trap and are unable to climb out again

  3. The sites for the pitfall traps are chosen randomly
• Ways to Minimise Potential Errors with Pitfall Traps

  1. Set several traps

  2. Disguise the opening with a cover, such as a leaf supported on sticks

  3. Check traps regularly or put 50% ethanol in the bottom of the traps
• Ways to Minimise Potential Errors with Quadrats

  1. Some of the type of plant being considered might be located partly inside and partly outside a quadrat

  2. A basic rule could be established and followed by everyone involved
• Sampling an Ecosystem


  1. We sample ecosystems to find out which plants and animals live there

  2. Find out how abundant these organisms are

  3. Investigate the reasons why the organisms live there

  4. It is usually impossible to count all the plants and animals living in an ecosystem so biologists use various methods for estimating the types and numbers of organisms present

  5. A sample can be taken to represent a population of organisms in an ecosystem

  6. To be representative several samples are taken
• Biological Keys

  1. Used for identifying organisms when sampling an ecosystem

  2. There are two different types of keys: Branched Keys and Paired Keys
• Random Sampling is important because it means that every individual in a population has an equal chance of being selected
• Levels of water and air pollution can be indicated by Indicator Species
• Indicator Species


  Species that by their presence, abundance, or absence indicate environmental quality/levels of pollution in the environment
• Reliability of Results


  The extent to which an experiment yields the same results on repeated trials. Large numbers of samples should be taken and an average calculated to increase reliability
• Investigating the effect of an abiotic factor on the distribution of organisms

  Setting up a line transect
• Abiotic factors


  Can impact both the variety and the number of organisms found within an ecosystem