Edexcel A Level (IAL) Biology -4.16-4.18 Biodiversity & Endemism- Study Notes- New Syllabus
Edexcel A Level (IAL) Biology -4.16-4.18 Biodiversity & Endemism- Study Notes- New syllabus
Edexcel A Level (IAL) Biology -4.16-4.18 Biodiversity & Endemism- Study Notes -Edexcel A level Biology – per latest Syllabus.
Key Concepts:
4.16 understand what is meant by the terms biodiversity and endemism
4.17 know how biodiversity can be measured within a habitat using species richness, and within a species using genetic diversity by calculating the heterozygosity index: $\text{heterozygosity index} = \frac{\text{number of heterozygotes}}{\text{number of individuals in the population}}$
4.18 understand how biodiversity can be compared in different habitats using the formula to calculate an index of diversity (D): $D = \frac{N(N-1)}{\sum n(n-1)}$
Biodiversity & Endemism
🌱 Introduction
Life on Earth exists in an incredible variety of forms from bacteria and fungi to plants and animals. To study and protect this variety, biologists use two key terms: biodiversity and endemism.
🧬 What is Biodiversity?
Definition:
Biodiversity means the variety of all living organisms on Earth at all levels, from genes to ecosystems.
Levels of Biodiversity
| Level | Description | Example |
|---|---|---|
| Genetic diversity | Variation in genes within a species | Different coat colors in dogs |
| Species diversity | Variety of species in a habitat | Coral reefs with fish, corals, sponges |
| Ecosystem diversity | Range of different habitats on Earth | Forests, deserts, wetlands, oceans |
Key idea:
The greater the biodiversity, the more stable and resilient the ecosystem becomes – it can recover faster from changes or damage.
🌍 What is Endemism?
Definition:
Endemism means when a species is found naturally in only one specific geographic location and nowhere else in the world.
Examples of Endemic Species
| Species | Endemic Location | Note |
|---|---|---|
| Lemurs | Madagascar | Evolved in isolation after the island separated |
| Kangaroos | Australia | Adapted to dry grasslands and open habitats |
| Giant Tortoises | Galápagos Islands | Result of long-term island isolation |
| Nilgiri Tahr | Western Ghats (India) | Example of Indian endemism |
Reason for Endemism:
- Isolation (islands, mountains, valleys)
- Unique climate or habitat conditions
- Long evolutionary history without migration
⚠️ Importance of Studying Both
- Biodiversity helps measure the health of ecosystems.
- Endemism helps identify unique and fragile regions (called biodiversity hotspots).
- Many endemic species are highly vulnerable to extinction because they exist in limited areas.
🧩 Summary Table
| Term | Meaning | Example | Importance |
|---|---|---|---|
| Biodiversity | Variety of life at all levels (genes, species, ecosystems) | Amazon rainforest | Indicates ecosystem health |
| Endemism | Species unique to one region | Kangaroo (Australia) | Marks ecological uniqueness, needs protection |
⚡ Quick Recap
Biodiversity = total variety of life on Earth.
It includes genetic, species, and ecosystem diversity.
Endemism = species found only in one specific location.
High biodiversity → stable ecosystem.
Endemic species → often more threatened by habitat loss.
Measuring Biodiversity
🌱 Introduction
To protect and compare ecosystems, biologists need a scientific way to measure biodiversity — both between and within species. Two key approaches are used:
- Species Richness → biodiversity within a habitat
- Genetic Diversity → biodiversity within a species
🧬 Species Richness (Biodiversity Within a Habitat)
Definition:
The number of different species present in a particular habitat.
How it’s measured:
- Take samples from the habitat (using quadrats or transects).
- Identify and count all the species found.
- The more species → the richer (more diverse) the habitat.
| Example | Explanation |
|---|---|
| A forest with 25 plant species | Higher species richness |
| A crop field with only 1 species | Low species richness |
Tip:
Species richness gives a simple idea of diversity but doesn’t consider how many individuals belong to each species (that’s species evenness, studied separately).
🧩 Genetic Diversity (Biodiversity Within a Species)
Definition:
The variety of alleles (gene variants) present in a population. It shows how much genetic variation there is among individuals of the same species.
Measured using the Heterozygosity Index (H):
\( H = \frac{\text{Number of heterozygotes}}{\text{Total number of individuals in the population}} \)
Example:
If in a population of 100 animals, 36 are heterozygous for a gene:
\( H = \frac{36}{100} = 0.36 \)
So, heterozygosity = 0.36 → meaning 36% of individuals carry two different alleles.
| Heterozygosity Index (H) | Meaning |
|---|---|
| High (→ 1) | High genetic diversity (many different alleles) |
| Low (→ 0) | Low genetic diversity (inbreeding or population bottleneck) |
Why it matters:
- High genetic diversity → better adaptation to environmental changes.
- Low genetic diversity → higher risk of disease & extinction.
🌍 Summary Table
| Measure | Level of Biodiversity | Formula / Method | What It Shows |
|---|---|---|---|
| Species Richness | Within a habitat | Count number of different species | Habitat diversity |
| Heterozygosity Index (H) | Within a species | \( H = \frac{\text{heterozygotes}}{\text{total individuals}} \) | Genetic variation |
⚡ Quick Recap
Species richness = number of different species in a habitat.
Genetic diversity = variation within a species’ genes.
Heterozygosity index (H) = heterozygotes ÷ total individuals.
Higher H → greater adaptability and survival potential.
Both are crucial for understanding ecosystem health and conservation value.
Comparing Biodiversity Using the Index of Diversity (D)
🌱 Introduction
Biodiversity can vary greatly between habitats – for example, a rainforest is far more diverse than a wheat field. To compare biodiversity quantitatively, scientists use a numerical index called the Index of Diversity (D).
🧬 Formula for Index of Diversity
\[ D = \frac{N(N – 1)}{\sum n(n – 1)} \]
| Symbol | Meaning |
|---|---|
| N | Total number of organisms of all species |
| n | Number of individuals of each species |
| Σn(n – 1) | Sum of n(n – 1) for all species in the habitat |
| D | Index of diversity |
🔹 Step-by-Step Calculation
Example: A woodland habitat contains:
| Species | Number of Individuals (n) |
|---|---|
| A | 10 |
| B | 20 |
| C | 30 |
Step 1: Calculate total N
\[ N = 10 + 20 + 30 = 60 \]
Step 2: Calculate n(n − 1) for each
\[ 10(9) = 90,\; 20(19) = 380,\; 30(29) = 870 \]
Step 3: Add them up
\[ \sum n(n – 1) = 90 + 380 + 870 = 1340 \]
Step 4: Substitute in formula
\[ D = \frac{60(59)}{1340} = \frac{3540}{1340} = 2.64 \]
Index of diversity = 2.64
🌳 Interpreting D
| Value of D | Meaning | Example |
|---|---|---|
| High D | High biodiversity – many species with fairly even numbers | Rainforest, coral reef |
| Low D | Low biodiversity – few species, or one dominant species | Farmland, desert |
Note: Higher D → greater species richness and evenness. D has no fixed maximum, so comparisons are relative between habitats.
🌍 Why Compare Biodiversity?
- To study impact of human activity (deforestation, pollution, etc.).
- To identify ecosystem health and stability.
- To guide conservation priorities.
🧩 Summary Table
| Measure | Formula | What It Shows | High Value Means |
|---|---|---|---|
| Index of Diversity (D) | \[ D = \frac{N(N – 1)}{\sum n(n – 1)} \] | Biodiversity of a habitat | More species, balanced populations |
⚡ Quick Recap
D = N(N − 1) ÷ Σn(n − 1)
N = total organisms, n = number in each species.
High D → high biodiversity and more stability.
Low D → one species dominates, less stable.
Used to compare biodiversity between different habitats.