How humans are changing ecosystems

Geography · Ecosystems

Which impact is behind it?

Seven real cases, four types of human impact. Pick a case, then pick the impact behind it. The places are examples of impacts that happen in many parts of the world.

7 of 7 still to sort.

Predict, then check

Think about what a garden plant could do once it gets out.

Japanese knotweed was brought to the UK from Asia in the 1800s as a garden plant. What do you predict happened next?

What you need to know

• An ecosystem is a natural environment where plants and animals interact; biodiversity is all the living things in an ecosystem or area.
• People change ecosystems and reduce biodiversity in four big ways: deforestation, pollution from farming and industry, climate change and invasive species.
• Deforestation means cutting down large areas of trees, usually for farming, building or logging.
• No trees, no habitats: animals decline, biodiversity falls, and a species can go extinct — die out completely.
• Have a goSam says: “Cutting down a forest only removes trees. Nothing else is affected.” Sam is confidently wrong. What else goes with the trees?

  The habitats — so animals decline, biodiversity falls and species can go extinct.

  Sam treats trees as stand-alone objects, but they are habitats too, so removing them removes homes for other living things.

• Fewer trees also means less transpiration (water evaporating from leaves), so less rainfall and a drier climate where plants struggle.
• Farming and industry pollute: fertiliser run-off feeds algal blooms, and factories can release harmful chemicals into air, water and soil.
• Have a goHeavy rain falls on a heavily fertilised field beside a river. Who benefits first: the fish or the algae?

  The algae — the extra nutrients feed them into algal blooms.

  “Extra nutrients” sounds like free food for everyone, but in the river it is the algae that get fed first, not the fish.

• Invasive species are brought somewhere they don’t naturally belong, usually by humans, and can outcompete the native species.
• Climate change, mostly from burning fossil fuels, melts ice, shifts where species can live and brings more wildfires, droughts and storms.
• Fewer species make a weaker ecosystem: biodiversity loss means less resilience to disease, drought, invasive species and climate change.
• Have a goTwo forests: one rich in different species, one that has lost many. A new disease reaches both. Which is more likely to cope, and why?

  The species-rich one — biodiversity loss makes an ecosystem less resilient to disease.

  It is tempting to think fewer species means less for the disease to harm, but losing species weakens the ecosystem, so it is more likely to struggle.

• Ecosystems give people food, clean water, clean air, medicines and climate regulation for free — these are ecosystem services.

The big picture

People change ecosystems through deforestation, pollution from farming and industry, climate change and invasive species. These impacts link together, reduce biodiversity and leave ecosystems less resilient — which puts at risk the free ecosystem services that people rely on.

⚠ Watch out

Treating each loss as a one-off: “a few trees, a few species, no big deal”. Impacts link up — fewer trees can dry the climate, a drier climate makes plants struggle, and every species lost leaves the ecosystem less resilient.

Memory hook

Keep asking “and then what?” until the trail reaches people: trees → habitats → species → a weaker ecosystem → fewer free services.

Check yourself

Choose fertiliser or deforestation. Write its “and then what?” trail in four or five steps, ending with why it matters to people.