Studying ecosystems and predator-prey relationships Revision Notes | GCSE OCR Foundation Biology

What this lesson covers

Learn about ecological sampling methods using transects and quadrats, and understand predator-prey cycles in stable communities.

• Explain how ecologists use quadrats and transects to study ecosystems
• Calculate population density and percentage cover from quadrat data
• Describe predator-prey relationships and their cyclical patterns
• Analyse data from ecological surveys to determine species distribution

Key ideas to keep in view

Use this lesson to stay inside B4.1 Ecosystems while connecting the detail back to the wider B4: Community level systems topic.

• B4: Community level systems
• B4.1 Ecosystems
• GCSE OCR Foundation Biology

Lesson notes preview

Read the core explanations from Studying ecosystems and predator-prey relationships before testing yourself from memory.

• Imagine you're a wildlife manager trying to save an endangered butterfly. How many are left? Where do they live? What's eating them? Without answers, your conservation efforts are just guesswork.
• Ecologists face this challenge daily. They need precise methods to count organisms, map their distribution, and understand the relationships between species. This isn't just academic curiosity — it's essential for conservation, agriculture, and managing our environment.
• The tools they use are surprisingly simple: a square frame called a quadrat and a measuring tape for transects. But the insights they reveal are profound. Let's see how these basic tools unlock the secrets of ecosystems.
• A square frame, usually 1m × 1m, placed randomly on the ground to sample organisms in a specific area. Used to estimate population density and percentage cover of species.
• Picture a 1m × 1m square frame thrown randomly onto a meadow. Everything inside that square gets counted — every daisy, every blade of grass, every beetle. This is quadrat sampling, and it's how ecologists turn vast, complex ecosystems into manageable data.
• The key word is 'random'. You can't just pick the prettiest spots or avoid the muddy areas. Random sampling eliminates bias and gives you a true picture of what's really there. Ecologists use random number generators to choose coordinates, ensuring their samples represent the whole ecosystem.
• But what exactly do you measure? For mobile animals like insects, you count individuals. For plants, you might measure percentage cover — what fraction of the quadrat area each species occupies. A large oak tree might cover 80% of a quadrat, while scattered daisies might cover just 5%.
• Quadrats tell you what's in one spot, but ecosystems aren't uniform. Walk from a pond edge to dry land, and you'll see species change dramatically. Water lilies give way to reeds, then to grasses, then to trees. This is where transects come in.
• A line or belt across a habitat used to study how species distribution changes along an environmental gradient such as distance from water, altitude, or soil pH.
• A transect is like drawing a line across your ecosystem and recording everything that touches it. There are two main types: line transects (record only what touches the line) and belt transects (record everything within a strip, like a series of connected quadrats).

Continue through the topic

Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.