Biodiversity — practice questions

Step 1: Calculate N (total individuals) for each woodland.

• Woodland P: N = 50 + 10 + 12 + 8 + 20 = 100
• Woodland Q: N = 15 + 15 + 15 + 15 + 40 = 100

Step 2: Calculate Σ(n/N)² for Woodland P.

• Oak: (50/100)² = 0.25
• Ash: (10/100)² = 0.01
• Birch: (12/100)² = 0.0144
• Sycamore: (8/100)² = 0.0064
• Holly: (20/100)² = 0.04
• Σ(n/N)² = 0.25 + 0.01 + 0.0144 + 0.0064 + 0.04 = 0.3208

Step 3: Calculate D for Woodland P.

• D = 1 - 0.3208 = 0.6792

Step 4: Calculate Σ(n/N)² for Woodland Q.

• Oak: (15/100)² = 0.0225
• Ash: (15/100)² = 0.0225
• Birch: (15/100)² = 0.0225
• Sycamore: (15/100)² = 0.0225
• Holly: (40/100)² = 0.16
• Σ(n/N)² = (4 × 0.0225) + 0.16 = 0.09 + 0.16 = 0.25

Step 5: Calculate D for Woodland Q.

• D = 1 - 0.25 = 0.75

Step 6: Conclusion.

• Woodland P has D ≈ 0.68. Woodland Q has D = 0.75.
• Since 0.75 > 0.68, Woodland Q has a higher species diversity than Woodland P. Although both have the same species richness (5 species), the individuals in Woodland Q are more evenly distributed (higher species evenness), making it more diverse.

Part 1: Levels of Biodiversity (3 marks)

1. Species diversity: The variety of different species within a particular area, encompassing both species richness (number of species) and species evenness (relative abundance of each species).
2. Genetic diversity: The variety of alleles and genes within a population or species, providing the raw material for adaptation.
3. Ecosystem diversity: The variety of different habitats, communities, and ecological processes across a given region.

Part 2: Crucial for Ecosystem Stability (3 marks) Maintaining high biodiversity is crucial for ecosystem stability because:

1. Increased resilience: Diverse ecosystems are more resilient to environmental changes (e.g., disease, climate shifts) because if one species is negatively affected, others may be able to fulfil its role, preventing ecosystem collapse.
2. Enhanced productivity and nutrient cycling: A wider range of species can lead to more efficient utilisation of resources and faster rates of processes like nutrient cycling and decomposition, contributing to overall ecosystem health.
3. Complex food webs: High biodiversity supports more complex and stable food webs. If a predator's primary prey declines, it may have alternative food sources, preventing cascading effects through the ecosystem.