OCR A Level Biology

Revision Notes

6.5.1 Ecosystems

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Ecosystems

Ecosystems

  • Species do not exist by themselves in their own isolated environment, they interact with other species forming communities
  • These communities interact with each other and the environment they live in, forming ecosystems
  • An ecosystem is a relatively self-contained community of interacting organisms and the environment they live in, and interact with
  • There is a flow of energy within an ecosystem and nutrients within it are recycled
  • There are both living (biotic) components and non-living (abiotic) components within an ecosystem
  • Ecosystems vary greatly in size and scale
    • Both a small pond in a back garden and the open ocean could be described as ecosystems
    • An individual human being could also be described as an ecosystem; there are thousands of species of bacteria living on and in every person

  • Ecosystems vary in complexity:
    • A desert is a relatively simple ecosystem
    • A tropical rainforest is a very complex ecosystem

  • No ecosystem is completely self-contained as organisms from one ecosystem are often linked to organisms from another
    • For example, birds are able to fly long distances to feed from multiple ecosystems

Example of an ecosystem

  • A forest is a perfect example of a complex ecosystem
    • There is a large community of organisms including trees, birds, small and large mammals, insects, bacteria, and fungi
    • The non-living components of the ecosystem include the soil, dead leaves, water from the rain and streams, the rocks, and any other physical or chemical factors
    • The non-living components of the ecosystem influence the community of organisms

Biotic Factors

  • A biotic factor is anything that influences the populations within a community that is a result of another organism's activity

Examples of Biotic Factors

  • Predation
  • Competition (inter-specific) for space, food, water, light etc.
  • Cooperation between organisms (can be between the same species or different species)
  • Parasitism
  • Disease
    • Pathogenic disease caused by microorganisms e.g. cholera, or carried by vectors e.g. malaria

  • Camouflage
    • A well-camouflaged prey animal will escape capture and not benefit the potential predator species

  • Mimicry
    • A hoverfly is harmless, yet it has evolved body colouring like that of a wasp. This deters potential predators into thinking that it is a wasp and could deliver a harmful sting

  • Mankind
    • Arguably the largest biotic factor of all, in terms of habitat loss, hunting, farming etc

Abiotic factors

  • An abiotic factor is any physical or chemical factor (non-living) that influences the populations within a community
  • The environmental conditions can majorly impact the spread of a species

Examples of Abiotic factors

  • Availability of water
  • Light
  • Radiation
  • Temperature
  • Turbidity ('cloudiness') of water
  • Humidity
  • Atmospheric composition
  • pH
  • Salinity
  • Soil composition

Exam Tip

When describing abiotic factors, be as precise as possible. For example, there are aspects of water that affect aquatic organisms: salinity, flow rate, mineral content, turbidity, depth, and dissolved oxygen concentration. It is a good idea to specify which aspect of 'water' that you mean.

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