2. Distribution of Organisms

• Abiotic factors are non-living variables that can influence where an organism lives.
• Examples of abiotic factors:

  • Light intensity
  • Temperature
  • Soil pH
  • Soil moisture
• Light meters are used to measure light intensity. Standing in the way of the light meter can shade the light meter and give it an inaccurate reading.
• The temperature of air can be measured by a thermometer.
• The temperature of soil can be measured with a probe. If left over soil is on the probe, inaccurate readings can be made. Ensure that the probe is cleaned after every use to solve this problem.
• Soil pH can be measured by inserting a soil pH probe into the ground. The same procedure is used with a moisture probe. If left over soil is on the probe, inaccurate readings can be made. Ensure that the probe is cleaned after every use to solve this problem.
• Biotic factors are living factors that can can influence where an organism lives.
• Examples of biotic factors

  • Predation
  • Disease
  • Competition for resources
  • Food availibility
  • Grazing
• You can work out how many organisms live in an area by using these techniques:

  • Quadrats
  • Pitfall traps
• Make sure you place the quadrants randomly so that results are accurate.
• Birds can find pitfall traps and eat the contents, giving a false reading. Camouflaging and hiding the traps can give more reliable, accurate results.
• Indicator species are species that indicate environmental quality and pollution levels by their presence or absence.
• Lichens are used as a biological indicator of air pollution.
• Freshwater invertebrates can be used as a biological indicator of water pollution.
• Rivers with a high oxygen concentration contains species such as Mayfly and Stonefly nymphs.