Ecosystems (OCR A Level Biology) : Revision Note

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