Ecosystems (OCR A Level Biology)

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