Interdependence & Competition (AQA GCSE Combined Science: Synergy: Life & Environmental Sciences): Revision Note

Competition

• If a group of organisms all need the same resource in order to survive and reproduce (have offspring) but there is a limited amount of the resource available, they are said to compete for the resource

• Competition can be between members of the same species (intraspecific competition) or between members of different species (interspecific competition)

Intraspecific competition between two grey squirrels (same species) for a limited resource

Interspecific competition between a grey squirrel and a red squirrel (different species) for a limited resource

• Plants in a community or habitat may compete with each other for certain limited resources:

• Animals in a community or habitat may compete with each other for certain limited resources:

Interdependence

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

• These relationships mean that species are interdependent

• For example:

  • Plants rely on insects such as bees for pollination

  • Many plants depend on animals to disperse their seeds

  • Animals may rely on plants or other animals for shelter and protection

  • Predators depend on prey species as a food source

  If one species is removed or its population changes significantly, it can affect many other species, not just those it feeds on or is eaten by

  • This can disrupt the balance of the entire community

• This interdependence means that changes to one population can cause knock-on effects throughout the community

• A stable community is one in which all the species and environmental factors are in balance, so that population sizes remain fairly constant over time

• A food web shows the interdependence of organisms by illustrating the feeding relationships between different species in a community

A food web shows the interdependence of organisms

• For example, in the food web above, if the population of earthworms decreased:

  • The population of grass plants would increase, as there are now fewer organisms feeding on them

  • The populations of frogs and mice would decrease significantly, as earthworms are their only food source

  • The population of sparrows would decrease slightly as they eat earthworms but also have another food source to rely on (caterpillars)