Ecosystems (AQA GCSE Geography): Revision Notes
2.1.1 Ecosystems
What is an Ecosystem?
An ecosystem includes all the living and non-living parts in an area.
Food Chains and Food Webs
A food chain shows what eats what. A food web shows lots of food chains and how they overlap.
Nutrient Cycle
When dead material is decomposed, nutrients are released into the soil. The nutrients are then taken up from the soil by plants. The plants may be eaten by consumers. When the plants or consumers die, the nutrients are returned to the soil.This transfer of nutrients is called the nutrient cycle.
Components of an Ecosystem
- Tertiary Consumers: Top (apex) predators that feed on the animals below them in the food web and have no predators of their own.
- Secondary Consumers: Small carnivores that prey on primary consumers.
- Primary Consumers: Herbivores that eat producers.
- Producers: Plants in an ecosystem. They form the foundation of food webs. Without producers, the ecosystem cannot support any other fauna.
- Decomposers: Organisms that break down dead organic matter, helping return nutrients to the soil.
Components of an Ecosystem
Impact of Changes in an Ecosystem
A change to one part of an ecosystem has an impact on other parts.
Some parts of the ecosystem depend on the others, e.g., consumers depend on producers for a source of food, and some depend on them for a habitat. If one part changes, it affects all the other parts that depend on it.
Example of a linked ecosystem:
| Component | Effect | Reason |
|---|---|---|
| Reduction in common oak trees | Leads to a decrease in the population of beetles and moth caterpillars | Beetles and moth caterpillars rely on oak trees for food |
| Decrease in beetles and moth caterpillars | Causes a decline in the number of woodpeckers | Woodpeckers feed on beetles and moth caterpillars |
| Decline in woodpecker population | Results in a reduction in the number of owls | Owls feed on woodpeckers and other small birds that eat caterpillars |
| Overall effect | Affects the entire food chain, leading to imbalances in the ecosystem | Each species is interconnected, and changes in one affect others |
