Ecosystems

• Populations of different species


  Form a community
• Community


  The living components of an environment
• Ecosystem


  A community and the non-living components of its environment together
• Ecosystems can range in size from the very small to the very large
• Ecosystems


  • They are dynamic systems
  • Populations constantly rise & fall
  • Any small change can have a large effect
  • Biotic & abiotic factors may alter the conditions of the ecosystem
• Biotic factors


  Living factors
• Abiotic factors


  Non-living factors
• Niche


  The role of a species within its habitat, consisting of both its biotic & abiotic interactions
• Different species having different niches are useful as it reduces competition for resources
• Abiotic factors that affect population growth

  • Temperature
  • Light
  • pH
  • Water & humidity
• Carrying capacity


  The maximum size of population of a species that an ecosystem can support
• Factors that affect carrying capacity

  • The effect of abiotic factors
  • Interspecific competition
  • Intraspecific competition
  • Predation
• Predator-prey relationship


  1. Prey is eaten by the predator

  2. Predator population grows

  3. Population of prey reduces

  4. Lack of food for predators means the population falls

  5. Population of prey recovers
• Estimating population size using quadrats

  1. Randomly placed quadrats

  2. Divide area into sections

  3. Obtain random coordinates

  4. Count number/frequency in a quadrat

  5. Calculate mean/average number
• Estimating population size using mark-release-recapture

  1. Capture sample, mark & release

  2. Collect a second sample

  3. Number in first sample × number in second sample divided by number of marked in second sample/number recaptured
• The mark-release-recapture method can produce unreliable results in big areas
• Assumptions made when using mark-release-recapture


  • Marked individuals distribute evenly
  • No migration in or out of the population
  • Few births or deaths
  • Method of marking does not affect survival
  • Mark does not come off
• Primary succession


  1. Colonisation by pioneer species

  2. Pioneers change the environment

  3. Environment becomes less hostile for new species

  4. Change/increase in diversity/biodiversity

  5. Climax community
• Climax community


  The final stage of succession, where the ecosystem is balanced & arable
• At each stage in succession, certain species may be recognised which change the environment so that it becomes more suitable for other species with different adaptations
• Secondary succession


  Occurs in a previously colonised area in which an existing community has been cleared
• Changes that organisms produce in their abiotic environment can result in a less hostile environment and change biodiversity