Edexcel International A Level Biology

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5.11 Ecology: Key Terms

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Ecology: Key Terms


  • Species are adapted, or well-suited, to life in a particular habitat
  • A habitat can be defined as the place where an organism lives
    • A habitat can be large, e.g. a desert, or small, e.g. an individual tree
      • Small habitats are sometimes referred to as microhabitats
    • Some species are habitat specialists, meaning that they can only survive in a very specific type of habitat, while others are generalists and can survive in a range of habitats
      • Generalists are more likely to be able to invade and take over a new habitat; such species are known as invasive species 
        • Humans sometime release new species into a habitat, either accidentally or on purpose; these species can disrupt the normal species interactions in a habitat and cause serious problems


  • When a species is found in a habitat, that habitat is said to support a population 
  • A population can be defined as all of the individuals of one species living in a habitat
    • The size of a population can be measured; this is the abundance of a species in a habitat
    • The exact location of a population within a habitat is a species' distribution within that habitat


  • Species do not exist by themselves in their own isolated environment; they interact with other species, forming communities
  • A community can be defined as multiple populations living and interacting in the same area
    • For example, a garden pond community is made up of populations of fish, frogs, newts, pond snails, damselflies and dragonflies and their larvae, pondweed, water lilies, and all other populations living in the pond


  • Communities interact with the non-living components of the habitat they live in, forming ecosystems
  • An ecosystem can be defined as a community and its interactions with the non-living parts of its habitat
    • There is a flow of energy within an ecosystem and nutrients within it are recycled
    • There are both biotic and abiotic components within an ecosystem
    • Ecosystems vary greatly in size and scale
      • A small pond in a back garden and the open ocean could both be described as ecosystems
    • 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 can often move to another
      • E.g. birds and aquatic animals are able to migrate long distances to feed from multiple ecosystems

Levels of Organisation in an Ecosystem

Individual members of a species together in a habitat form a population, populations interact within a community, and communities interact with each other and with non-living components of their habitat to form an ecosystem.

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Naomi H

Author: Naomi H

Naomi graduated from the University of Oxford with a degree in Biological Sciences. She has 8 years of classroom experience teaching Key Stage 3 up to A-Level biology, and is currently a tutor and A-Level examiner. Naomi especially enjoys creating resources that enable students to build a solid understanding of subject content, while also connecting their knowledge with biology’s exciting, real-world applications.