The big idea: People do not only drive single species extinct. They destroy whole ecosystems: the community and the place it lives in.
The points to remember
- Ecosystem loss: a whole ecosystem, such as a forest, wetland or reef, is destroyed or replaced.
- Direct human causes: logging, clearing land for farms and plantations, mining, building dams, towns and roads, draining wetlands.
- Indirect human causes: pollution, and the climate change caused by burning fuels.
- When an ecosystem goes, every species in it loses its habitat at once.
- Only causes that are anthropogenic (made by people) count here.
Remember it as: Gone with the whole place.
Anthropogenic
- A dam floods a forest
- Logging and plantations
- Draining a wetland for farms
Natural
- Lightning starts a fire
- A long drought kills trees
- Insects eat leaves and saplings
Real example: a dam: When the Three Gorges Dam in China filled, its reservoir flooded more than 600 km of the Yangtze valley, drowning forests, fields and river habitats.
Check who caused it:
Natural events do not count: A fire started by lightning, a drought or an insect outbreak is not anthropogenic. A dam that floods a forest is.
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The big idea: In Southeast Asia, mixed dipterocarp forest is being logged and replaced with plantations: a whole ecosystem lost.
The points to remember
- Mixed dipterocarp forest: tall rainforest of many tree species, many of them dipterocarps, in Borneo, Sumatra and Malaysia.
- Logging takes out the valuable trees and cuts roads into the forest.
- The rest is cleared and burned for oil palm and other plantations.
- Species lose habitat, food and shelter; soil washes away and floods increase.
- Satellite images show the loss year by year; better images now show even small clearings.
Real example: Borneo: Satellite images show that about 30% of Borneo's forest, much of it dipterocarp forest, was lost between 1973 and 2010, mostly to logging and oil palm plantations.
Read a deforestation map or graph carefully:
Logging and plantations, not rewilding: Forest lost on a map is explained by logging and plantations. Rewilding and afforestation add forest; they cannot explain a loss.
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The big idea: A second case study comes from closer to home: an ecosystem that people have destroyed in a region you know.
The points to remember
- Choose an ecosystem lost from your own region: a drained marsh, a cleared forest, a ploughed grassland or a shrunken lake.
- Name the human cause: farming, water extraction, building or pollution.
- Say what was lost: the habitat, the species that lived there and the services it gave people.
- Use the same three steps for the dipterocarp forest: cause, loss, effect on species.
Remember it as: Cause, loss, effect.
Cause
- What people did: diverted water, ploughed, cleared, built
Loss
- The habitat and community that disappeared
Effect
- Species gone from the area; services lost
Real example: the Aral Sea: From the 1960s, the rivers feeding the Aral Sea in Central Asia were diverted to water cotton fields. The lake shrank to a small fraction of its size and its fishing industry and lake ecosystem collapsed.
Make it about the place:
Name the ecosystem: Say which ecosystem was lost, such as a lake or a prairie, not only which species. That is what makes it ecosystem loss.
How it is tested: Paper 1A: which cause is human, or which activities explain forest loss on a map. Paper 1B: read deforestation graphs. Paper 2: outline or explain how deforestation affects biodiversity.
IB-style questionOutline[2 marks]
Large areas of mixed dipterocarp forest in Malaysia have been replaced by oil palm plantations. Outline two ways in which this affects biodiversity.
Model answer plan
See the answer broken into clear points, with guidance on how each point earns marks.
Human, not natural: Only human causes count here. A dam, logging or a plantation is human; lightning, a drought or an insect outbreak is natural.