changes to an ecosystem

• human activities


  • use of agricultural fertilisers - can lead to eutrophication
  • ponds drained for farming - plants and fish can die
  • woods cut down - destroys habitats for wildlife and affects the nutrient cycle
  • hedgerows removed - destroys habitats, which changes the plant and animal balance
• the effects of adding perch to a pond

  1. the perch will eat more of the smaller fish and small animals (frogs)
  2. this will reduce the amount of food for creatures further up the food chain
  3. with fewer frogs, there will be an increase of creatures below frogs in the food chain
• trophic cascade


  when a predator is removed from an ecosystem, causing a chain reaction in changes in the food chain
• factors that cause changes to an ecosystem

  • extreme weather events
  • land use change
  • alteration to water and soils
  • climate change and global warming
  • spread of invasive species
  • hunting or trapping animals
• the effect of changes to an ecosystem

  • ecosystems adapt slowly to natural changes with few harmful effects, but rapid changes can have serious impacts
  • global example: climate change
  • small scale example: changes to a habitat (when a hedge is removed)
• natural change

  • drought due to climate change - could dry up ponds and lakes, meaning that plants will dry out/die and fish could be starved of oxygen and die
• yellowstone national park


  • in 1995, wolves were reintroduced to the yellowstone national park
  • effects: deer started avoiding certain parts of the park (as they could be killed by wolves), the height of trees quintupled in 6 years, number of birds increased and the rivers meandered and eroded less and channels narrowed
  • example of a trophic cascade
• eutrophication

  1. when agricultural fertilisers (containing nitrate) gets washed into rivers which allow algae to grow
  2. the algae covers the surface of the rivers blocking out sunlight
  3. plants and fish don't get water and are starved of oxygen