IB Biology SLProtecting BiodiversityPaper 1 & 2Case studies~9 min read
Ecosystem Loss
Hunting removes one species at a time. Clearing a habitat removes everything at once — the plants, the animals, the fungi, the soil organisms and every relationship between them. That is why ecosystem loss does more damage to biodiversity than almost anything else.
📚 What you need to know
An ecosystem is all the living organisms in an area, their interactions with each other, and the non-living environment they live in.
Human activity damages and destroys ecosystems worldwide, most obviously through deforestation.
You need two case studies: mixed dipterocarp forest in Southeast Asia, plus one of your own choice.
Dipterocarps are a family of tropical trees that once dominated a complex rainforest ecosystem across Southeast Asia.
Some parts of Southeast Asia have lost more than 50% of their forest.
Forest is often removed by clear-cutting — taking every tree in an area — for timber and to free land for agriculture such as palm oil.
Replacing a forest with a plantation looks green but is close to a monoculture, with very low biodiversity.
What counts as an ecosystem
Definition — all three parts
Ecosystem = the living organisms in an area + their interactions + the non-living environment
That third part is easy to forget in an exam. Soil, water, light, temperature and mineral availability are all part of the ecosystem, and clearing a forest changes every one of them.
Case study 1: mixed dipterocarp forest, Southeast Asia
🧩 What to say about it
What it is. Dipterocarps are a family of tall tropical trees. They formed the backbone of a complex rainforest ecosystem that once covered much of Southeast Asia.
Why they matter. They create the canopy structure that everything else depends on — shade, humidity, nesting sites and food for a huge range of species.
What is happening. The forests are being gradually lost. In some parts of Southeast Asia more than half the forest has already gone.
How. Mainly clear-cutting, where every tree in an area is felled and removed.
Why. The timber is valuable, and the cleared land is used for agriculture, especially palm oil plantations.
Look at the heights. A rainforest has an understorey, a middle layer and an emergent canopy, each supporting different species. A plantation has one layer, one age and one species.
This is the point examiners are testing when they show you a photo of a plantation. “There are still trees” is not a defence. Ecosystem diversity, species diversity and genetic diversity have all collapsed.
What actually gets lost
An easy way to pick up marks is to explain the knock-on effects, not just the tree count.
Fragmentation is the quiet one. Two small patches with a road between them do not function like one large forest, because many species will not cross open ground.
Soil is part of it: tropical rainforest soil is often surprisingly thin, and most of the nutrients are held in the living plants rather than the ground. Remove the trees and heavy rain washes the topsoil away, which is why the forest struggles to grow back.
Case study 2: choosing your own
The second case study is yours to research. Same rules as before:
Choose an ecosystem from a local or familiar region.
The loss must be caused by human activity.
Match the level of detail of the dipterocarp example: what the ecosystem is, what is being lost, the human activity responsible, and the effect on biodiversity.
Commonly used examples include the Great Barrier Reef in Australia, the Northern Great Plains grassland in North America, and mangrove forests in many tropical coastal regions.
Example ecosystem
Main human pressure
Effect on biodiversity
Mixed dipterocarp forest, SE Asia
Clear-cutting for timber and palm oil
Canopy structure and microhabitats lost; forest species have nowhere to live
Great Barrier Reef, Australia
Warming seas, run-off from farmland, coastal development
Coral bleaching removes the structure that reef species depend on
Northern Great Plains, North America
Conversion of grassland to cropland
Native prairie plants replaced by monoculture; grassland animals decline
Mangrove forests, tropical coasts
Cleared for shrimp farms, ports and building
Nursery habitat for fish lost; coasts left exposed to erosion
Worked examples
WORKED EXAMPLE
Outline the causes of the loss of mixed dipterocarp forest in Southeast Asia. [3]
Point 1: the methodForest is removed by clear-cutting, in which all the trees in an area are felled and taken away.Point 2: the reasonsThe timber itself is valuable, and clearing frees land for agriculture such as palm oil plantations.Point 3: the scaleLoss has been gradual but large — parts of Southeast Asia have lost over half their forest
WORKED EXAMPLE
A student says a palm oil plantation is not a problem because it still has trees. Evaluate this statement. [4]
Step 1: concede the small pointIt is true that plant cover remains and some photosynthesis continues.Step 2: species diversityA plantation is effectively a monoculture: one tree species replaces hundreds, so species richness collapses.Step 3: ecosystem diversityThe layered canopy and its microhabitats are gone, so the animals, fungi and plants that needed them cannot survive there.Step 4: concludeThe statement is wrong — tree cover is not the same as a functioning, biodiverse ecosystem
WORKED EXAMPLE
Explain why habitat fragmentation reduces biodiversity even when the total area of habitat left is quite large. [3]
Point 1: patches are isolatedRoads and cleared land split the habitat, and many species will not cross open ground.Point 2: populations shrinkEach patch holds a smaller population, and small populations have lower genetic diversity.Point 3: the consequenceIsolated small populations are less able to adapt and are at higher risk of local extinctionNice link back to speciation: the barrier here is a road, not a river.
💡 Exam tip
Define ecosystem with all three parts: organisms, interactions, non-living environment.
Name the practice: clear-cutting. Naming the specific method usually earns the mark.
Give both reasons for clearing: timber and land for agriculture. Two reasons, two chances.
Have a figure ready: over 50% of the forest lost in parts of Southeast Asia.
List several consequences, not just habitat loss — fragmentation, soil erosion, carbon release and effects on local people all count.
Prepare your second case study in advance, with the same four headings as the dipterocarp one.
⚠ Common mix-up
Defining an ecosystem as just the living things. The non-living environment and the interactions are part of it.
Assuming replanting fixes it. A plantation of one species is not a restored ecosystem.
Confusing habitat loss with fragmentation. Loss removes habitat; fragmentation breaks what is left into isolated pieces.
Writing only about animals. Plants, fungi and soil micro-organisms are lost too, and marks are available for saying so.
Saying rainforest soil is rich. It is often thin, with most nutrients held in the living plants — which is why recovery is slow.
Picking a distant, vague second case study. A local one you can describe in detail scores better.
Up next: Loss of Biodiversity — how we actually measure the crisis, who collects the evidence, and why the IUCN red list matters.
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