Abiotic and Biotic Factors

• Abiotic factors


  Non-living factors
• Biotic factors


  Living factors
• Abiotic factors


  • Moisture level
  • Light intensity
  • Temperature
  • Carbon dioxide level (for plants)
  • Wind intensity and direction
  • Oxygen level (for aquatic animals)
  • Soil pH and mineral content
• Different organisms are adapted to different abiotic conditions
• A change in the environment (increase or decrease in an abiotic factor)

  Can affect the sizes of populations in a community
• A change in the environment (increase or decrease in an abiotic factor)


  Can affect the population sizes of other organisms that depend on them
• Changes in abiotic factors affecting plant populations

  • Decrease in light intensity, temperature or level of carbon dioxide could decrease the rate of photosynthesis
  • Decrease in the mineral content of the soil could cause nutrient deficiencies
• Biotic factors


  • New predators arriving
  • Competition
  • New pathogens
  • Availability of food
• A change in the environment (introduction of a new biotic factor)

  Can affect the sizes of populations in a community
• Changes in biotic factors affecting populations

  • A new predator could cause a decrease in the prey population
  • Grey squirrels outcompete the red squirrels, so the population of red squirrels is decreasing
• The following graph shows the effect of a new pathogen on Species A
• The population size of Species A was increasing up until 1985, when it decreased rapidly until 1990, suggesting that 1985 was the year that the new pathogen arrived
• The population started to rise again after 1990