Interdependence (AQA GCSE Biology Combined Science): Revision Notes
Interdependence
What is interdependence?
When one species is taken away from a community, it can change what happens to all the other species. This is called interdependence.
All living things in a community depend on each other to survive. They need each other for things like food, shelter, and reproduction.
Interdependence is a fundamental concept in ecology that explains how all living things in an ecosystem are connected and rely on each other for survival.
Stable communities
A stable community is when all the species living together are balanced and healthy.
What makes a community stable?
Understanding what creates stability in ecological communities is crucial for conservation efforts and ecosystem management.
In a stable community:
- All the environmental factors are balanced (like temperature, water, and nutrients)
- The population sizes stay roughly the same over time
- Each species can find what it needs to survive
Organisms get materials from their surroundings and from other organisms. This helps them survive and reproduce. Every species in the community depends on other species for resources like food and shelter.
How plants depend on other organisms
Plants need help from other organisms to reproduce and spread.
Pollination
Plants need pollination to reproduce. This means moving male gametes (pollen) to female gametes (egg cells).
- Some plants use wind to carry their pollen from one plant to another
- Other plants rely on bees and insects to transfer pollen when they visit flowers
Seed dispersal
Plants also need help spreading their seeds:
- Wind can carry seeds far away from the parent plant
- Animals help by eating fruits and carrying seeds in their fur or droppings
This partnership between plants and animals is called mutualism - both species benefit from the relationship.
Example: woodland community
A woodland shows how different species depend on each other. You can see this in food webs.
How species are connected
The complexity of these connections is what makes ecosystems resilient but also vulnerable to changes.
Woodland Food Web Connections
In a typical woodland ecosystem:
- Grass is eaten by rabbits and fieldmice
- Rabbits are eaten by foxes and sparrowhawks
- Fieldmice are eaten by foxes and sparrowhawks
- Sparrows eat seeds and berries, and are eaten by sparrowhawks
- Blackbirds eat berries and slugs
Each species has multiple food sources and multiple predators. This creates a web of connections.
What happens when species are removed?
When you remove one species from a community, it affects many others through a cascade effect.
Example effects
Scenario 1: Removing Blackberries
If blackberries were all eaten:
- There would be less food for rabbits and sparrows
- Rabbit and sparrow populations would get smaller
- Foxes and sparrowhawks would have less prey to hunt
- Their populations might also fall
Scenario 2: Removing Sparrowhawks
If sparrowhawks were removed:
- Sparrow populations would increase (no predator)
- More sparrows would eat more seeds and berries
- This could affect plant reproduction
- Other species that eat the same food might struggle
These examples show how removing just one species can create a ripple effect throughout the entire community. This is why conservation of all species, not just the popular ones, is so important.
Remember!
Key Points to Remember:
- Interdependence means species in a community depend on each other to survive
- Stable communities have balanced environmental factors and steady population sizes
- Plants need other organisms for pollination and seed dispersal
- Removing one species from a community affects many other species
- Food webs show how species are connected through what they eat and what eats them