Random quadrats and percentage cover, scaling a quadrat count up to a whole field, belt transects, the field investigation required practical, and capture-recapture for animals that move.
What you will learn
- Estimate a population from quadrats of any size
- Work out percentage cover and the area a plant covers
- Describe a transect and read how species change along it
- Plan a fair quadrat investigation
- Estimate an animal population by capture-recapture
Random quadrats
To compare two areas, put quadrats at random coordinates: lay two tape measures at right angles and use random numbers for the two distances.
You do not choose, so there is no bias. Use plenty of quadrats and take a mean.
number per m² = mean per quadrat ÷ area of one quadrat
population ≈ number per m² × total area
- 8 quadrats, each 0.5 m × 0.5 m = 0.25 m²; mean 3.5 buttercups per quadrat
- 3.5 ÷ 0.25 = 14 per m²
- field 60 m × 30 m = 1800 m², so about 14 × 1800 = 25 200 buttercups
A 0.5 m quadrat is not 0.5 m²: square the side.
Some plants are hard to count, so record percentage cover: in a quadrat of 25 squares, each square is 4%. A quadrat with the plant in 15 squares has 15 × 4 = 60% cover; with a mean cover of 40% over a 300 m² field, the plant covers about 0.40 × 300 = 120 m².
The rest of this lesson and its 12 practice questions are locked.
In this lesson
- Random quadrats
- Transects
- Capture-recapture
- Try it: Scale up a quadrat count
12 practice questions, marked as you go; about 25 minutes in all.
Key terms
Random, Belt transect, Too high
In this unit: Ecology
Communities and adaptations, sampling with quadrats, transects and capture-recapture, food chains and the carbon, water and nitrogen cycles, decay, parasitism and mutualism, eutrophication, biodiversity and human impact, biomass transfer and food security.
- Communities, interdependence and adaptations
- Sampling with quadrats, transects and capture-recapture
- Food chains, cycles and decay
- Biodiversity and human impact
- Trophic levels, pyramids and efficiency
- Food security and farming
- Biological control and bioaccumulation
- Fish farming, introduced species and the cycles in depth