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examBoard: Pearson Edexcel
examType: IGCSE
lessonTitle: Biodiversity Measurement
Biodiversity is all around us - from the tiniest microbes in the soil to the largest whales in the ocean. But how do scientists actually measure it? In this session, we'll explore the methods used to quantify biodiversity and why these measurements matter for conservation and ecosystem health.
Key Definitions:
Measuring biodiversity helps us to:
Biodiversity exists at multiple levels:
For IGCSE, we focus mainly on species diversity.
There are several ways to measure biodiversity, but the most common approach is to look at species diversity. This involves two main components:
This is simply the count of different species in an area. For example, if you find 5 different tree species in a forest, the species richness is 5.
Example: If you sample an area and find robins, blackbirds, sparrows and blue tits, your species richness is 4.
This measures how similar the numbers of each species are. High evenness means species are present in similar numbers.
Example: An area with 10 robins, 10 blackbirds, 10 sparrows and 10 blue tits has higher evenness than an area with 37 robins, 1 blackbird, 1 sparrow and 1 blue tit.
It's usually impossible to count every organism in an ecosystem, so scientists use sampling techniques to estimate biodiversity.
Square frames (usually 1m²) placed randomly in an area to count species within them.
Best for: Plants and slow-moving organisms
Lines across an area along which samples are taken at regular intervals.
Best for: Studying changes across gradients (e.g., from shore to inland)
Containers sunk into the ground to catch small animals that fall in.
Best for: Ground-dwelling invertebrates
Scientists use mathematical formulas called indices to combine species richness and evenness into a single value that represents biodiversity.
This is one of the most common biodiversity indices. The formula is:
D = 1 - Σ(n/N)²
Where:
The value of D ranges from 0 to 1, where:
The higher the value, the greater the biodiversity.
Imagine we sampled a woodland and found:
Total number of trees (N) = 30
For oak trees: (15/30)² = 0.25
For birch trees: (10/30)² = 0.11
For beech trees: (5/30)² = 0.03
Sum of these values = 0.39
Simpson's Diversity Index (D) = 1 - 0.39 = 0.61
This value (0.61) suggests moderate diversity.
When measuring biodiversity, it's important to understand the factors that might influence your results:
Once you've collected biodiversity data, what does it actually tell you?
Coral reefs are among the most biodiverse ecosystems on Earth, housing about 25% of marine species despite covering less than 1% of the ocean floor.
Scientists measure coral reef biodiversity using underwater transects and quadrats. They record fish species, coral types and other marine organisms.
Recent studies have shown declining biodiversity in many reefs due to:
By regularly measuring biodiversity, scientists can track the health of reefs and the effectiveness of conservation efforts.
Biodiversity measurements aren't just academic exercises - they have real-world applications:
Identifying biodiversity hotspots helps prioritize areas for protection.
Understanding ecosystem function and monitoring changes over time.
Guiding decisions about land use, resource extraction and restoration efforts.
Biodiversity measurement is a crucial tool for understanding and protecting our natural world. By quantifying the variety of life in different areas, we can make informed decisions about conservation and resource management.
Remember these key points:
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