Levels Of Organisation In An Ecosystem (AQA GCSE Combined Science: Synergy: Life & Environmental Sciences): Revision Note

Key Terms in Ecology

• There are several key terms that we use when referring to the various different components of an ecosystem and their levels of organisation:

• A population is defined as a group of organisms of the same species living in the same place at the same time

• A community includes all of the populations living in the same area at the same time

  • Within a community, each species depends on other species for food, shelter, pollination, seed dispersal etc

  • If one species is removed it can affect the whole community

  • This is called interdependence

• A habitat is the place where an organism lives

  • E.g. badgers, deer, oak trees and ants are all species that would live in a woodland habitat

• An ecosystem is defined as all the biotic factors and all the abiotic factors that interact within an area at one time

  • Biotic factors includes all the living components such as plants and animals

  • Abiotic factors includes all the non-living components such as light intensity, mineral ions, water availability

  • Ecosystems can vary greatly in size and scale

    • A small ecosystem might be a garden pond

    • A large ecosystem might be the whole of Antarctica

Levels of organisation in an ecosystem

Food Chains

• A simple way to show the feeding interactions between the organisms in a community is with a food chain

Producers in food chains

• Every food chain starts with a producer

  • Photosynthetic organisms are the producers of biomass for life on Earth

  • They produce their own food using energy from the Sun

  • A producer has the following characteristics:

    • They are at the start of every food chain (the first trophic level, which is always the biggest)

    • They can photosynthesise (producers are normally green plants or algae)

    • They make glucose by photosynthesis

    • They use this glucose to produce other biological molecules, which then make up the producer’s biomass

The steps of a food chain

1. Producer: food chains always begin with a producer

2. Primary consumer: producers are eaten by primary consumers (herbivores/omnivores)

3. Secondary consumer: primary consumers are eaten by secondary consumers (carnivores/omnivores)

4. Tertiary consumer: secondary consumers are eaten by tertiary consumers (carnivores/omnivores)

An example of a food chain

• A food chain shows the transfer of energy from one organism to the next

• The source of all energy in a food chain is light energy from the Sun

• The arrows in a food chain show the transfer of energy from one level of the food chain to the next

Predator-Prey Interactions

• Producers are eaten by primary consumers, which in turn may be eaten by secondary consumers who are themselves eaten by tertiary consumers

• Consumers that kill and eat other animals are predators, and those eaten are prey

  In a stable community the numbers of predators and prey rise and fall in cycles

• You should be able to interpret graphs used to model predator-prey cycles

An example of a graph used to model a predator-prey cycle between the Canadian lynx and the snowshoe hare

• The graph above demonstrates some of the key patterns of predator-prey cycles:

1. The number of predators increases as there is more prey available

2. The number of prey then decreases as there are now more predators

3. The number of predators decreases as there is now less prey available

4. The number of prey increases as there are now fewer predators

5. The cycle now repeats