To explain a habitat change, write each link of the food chain as a cause followed by a result. Do not jump from the change to the last animal.
This lesson is part of vegetation, climate and wildlife relationships. It builds on the evidence habits from comparing vegetation types carefully.
What does a chain of effects look like?
Each sentence carries one link. The first says what changed. The next says what that did to the organism that depends on it, and so on.
A useful opener for every sentence is “so”. It forces each result to follow from the cause before it.
Worked example: a cleared forest patch
This is an original scenario. A forest patch has fruit trees. Fruit is eaten by beetles, beetles by small birds, and small birds by a hawk.
Before clearing, the plot held 50 fruit trees. Clearing leaves 34 fruit trees standing.
Trees fall from 50 to 34, so 16 are lost, which is 16 ÷ 50 = 32%.
Now write the chain: “Clearing removes 32% of the fruit trees, so beetles have less fruit to eat. With less food the beetle number is likely to fall, so the small birds that feed on them have less prey. Fewer small birds then leave the hawk with a smaller food supply.”
The word likely is there because the survey gives tree numbers only, so the later steps are reasoned, not measured.
The mistake that loses marks
The weak answer is “Clearing the forest kills the hawk”. The link is one jump long, and no step is shown.
| Weak | Strong |
|---|---|
| Clearing kills the hawk. | Fewer trees means fewer beetles, so fewer small birds, so less prey for the hawk. |
| Animals lose their home. | The plot has 32% fewer fruit trees, which reduces food for beetles. |
Count the links in your answer. A chain with four organisms needs at least three links written out.
What evidence supports a link?
Quote a number for each link where you can. If the data gives only the first step, label later steps as reasoning, using words such as probably or may.
Add one balancing point if the data allows. Open ground may suit grass-eating insects, for example, so not every species loses. The claim and evidence revision desk helps you tighten each link.
Check yourself
A river mangrove strip is cut. Mangrove leaves feed crabs, and crabs feed a wading bird. Crab counts fall from 90 to 45 per plot. Write a chain and calculate the percentage fall.
Answer
Fall: 90 − 45 = 45, and 45 ÷ 90 × 100 = 50%.
Chain: cutting the mangroves removes leaf food, so crab numbers fall by 50%. With fewer crabs, the wading bird has less prey, so its numbers may also fall. The data does not count the birds, so the last step is reasoned only.
What to study next
Check that examples match your claims in using a location example only after checking its actual conditions. For a teacher to check your chains, see online one-to-one Geography tuition.