Ecosystems and Interdependence Notes

AQA GCSE Biology: Revision notes

Key facts

  • An ecosystem is a community of living (biotic) organisms interacting with the non-living (abiotic) environment.
  • Plants compete for light, space, water and mineral ions; animals for food, mates and territory.
  • Interdependence: species rely on each other, so removing one can affect the whole community.
  • A stable community has balanced species and factors, so populations stay fairly constant.
  • Adaptations can be structural, behavioural or functional; extremophiles live in extreme conditions.
  1. 1

    Organism

    one living thing

  2. 2

    Population

    one species in an area

  3. 3

    Community

    all populations

  4. 4

    Ecosystem

    plus the abiotic environment

Organism to ecosystem

Ecosystems and levels

An ecosystem is a community of living organisms interacting with the non-living parts of their environment.

An ecosystem includes the biotic (living) parts and the abiotic (non-living) parts, such as soil, water and climate.

It can be described at different levels of organisation, from one organism up to the whole ecosystem.

Interdependence and competition shape how a community works.

  1. 1

    Organism

    a single living thing

  2. 2

    Population

    all organisms of one species in an area

  3. 3

    Community

    all the populations in an area

  4. 4

    Ecosystem

    the community plus its abiotic environment

Levels of organisation, smallest to largest

What is a community?

Competition

Organisms compete for limited resources, which limits their population sizes.

Organisms in a community compete for limited resources. Not every individual can get enough to survive and reproduce, so competition limits population size.

  1. 1

    Limited resources

    light, space, water, food, mates, territory

  2. 2

    Competition

    individuals and species compete for them

  3. 3

    Not all survive

    some cannot get enough to reproduce

  4. 4

    Population limited

    numbers stay below an upper limit

Competition for limited resources keeps populations in check.

Plants

  • Light
  • Space
  • Water
  • Mineral ions

Animals

  • Food
  • Mates
  • Territory

Which do animals compete for?

Interdependence

Each species depends on others for food, shelter, pollination or seed dispersal, so losing one affects the rest.

Interdependence means species in a community rely on one another for food, shelter, pollination and seed dispersal.

If one species is removed, species that depended on it can be affected too. In a stable community all species and environmental factors are in balance, so population sizes stay fairly constant.

  1. 1

    Bees removed

    pollinators are lost

  2. 2

    Plants

    fewer flowering plants reproduce

  3. 3

    Animals

    those that eat the plants lose food

Losing one species

What is a stable community?

Adaptations

Adaptations can be structural, behavioural or functional, and extremophiles are adapted to extreme conditions.

Organisms are adapted to their natural environment.

Organisms in very high temperature, pressure or salt concentration are called extremophiles.

  1. 1

    Challenge in the environment

    cold, drought, predators or extreme conditions

  2. 2

    Adaptation

    structural, behavioural or functional

  3. 3

    Better survival

    the organism copes with the challenge

  4. 4

    Reproduces

    passes the adaptation to offspring

How an adaptation helps an organism survive.

Structural

  • A physical feature
  • Thick fur

Behavioural

  • A way of acting
  • Migration

Functional

  • A process inside the body
  • Making antifreeze proteins

Migration is an example of which type of adaptation?

Abiotic and biotic factors

Non-living (abiotic) and living (biotic) factors both affect the organisms in a community.

Ask whether a factor is a living thing or interaction (biotic) or a physical or chemical condition (abiotic).

  1. 1

    Factor changes

    abiotic (e.g. temperature falls) or biotic (e.g. a new predator)

  2. 2

    Organisms affected

    survival, growth or reproduction change

  3. 3

    Populations change

    numbers rise or fall

  4. 4

    Community changes

    other species are affected in turn

A change in either kind of factor can change a community.

Abiotic (non-living)

  • Light intensity
  • Temperature
  • Moisture levels
  • Soil pH and minerals
  • Wind and gas levels

Biotic (living)

  • Availability of food
  • New predators
  • New pathogens
  • One species outcompeting another

Which is an abiotic factor?

Try an exam question

Explain what is meant by interdependence in a community, and why removing one species can affect others.

[3 marks]

That's the notes covered.

Carry on to the next subtopic.