10.3

• Biotic factors

  • Predation
  • Reproductive partners
  • Territory
  • Parasitism/Disease
• Abiotic factors

  • Light intensity
  • Temperature
  • Wind and water currents
  • Water availability
  • Oxygen availability
  • Edaphic factors (relating to the structure of soil)
• Density-dependent factors

  Factors that can influence population size, such as predation, parasitism, food source
• Gales/hurricanes

  • Destroy habitats
  • Organisms have to flow with the current, attach to surfaces, or be strong swimmers to survive
• Water availability

  • Organisms need water to survive unless adapted to very low water levels
• Oxygen availability

  • Oxygen necessary to survive, may be a problem in stagnant or hot water or waterlogged soil where air spaces fill with water
• Edaphic factors

  • Sandy soil leaches minerals as water passes through quickly, drains quickly
  • Clay gets waterlogged as difficult to drain, take too long to warm, hard to work
  • Ideal soil is loam which is a mixture of types
• Types of competition

  • Interspecific competition between individuals of different species
  • Intraspecific competition between individuals of the same species
• Primary succession


  Where an area previously devoid of life is colonised by a community of organisms
• Process of primary succession

  1. Pioneer species, able to survive harsh conditions, colonise the area

  2. They die, decompose, and add nutrients to the ground

  3. Over time, this allows more complex organisms to survive
• Climax community

  The final stage of succession, where the ecosystem is balanced and stable. It is reached when the soil is rich enough to support large trees or shrubs, and the environment is no longer changing
• Plagioclimax

  Where human intervention prevents the expected climax community from forming. This may be done in the interests of conservation
• Define Biotic factors

  Living features of an ecosystem e.g. predators, disease
• How can biotic factors affect population size?

  Can affect population size through:

  • predator/prey oscillations
  • disease reducing population
  • availability of mates
• Define Abiotic factors

  Non-living features of an ecosystem e.g. light, temperature
• How can abiotic factors affect population size?

  Can affect population size through:

  • light affects circadian rhythms, influences plant growth
  • temperature affects enzyme activity,
  • adverse weather conditions require certain adaptations
  • availability of water and oxygen
• Intraspecific competition

  Competition between organisms of the same species
• Interspecific competition

  Competition between organisms of different species