Biodiversity and conservation
Domain 3 tests biodiversity at genetic, species and habitat levels, its measurement, threats and conservation. Questions often require Simpson's index, evaluation of conservation strategies and analysis of human impacts.
Core rules
- Species richness counts species; evenness describes relative abundance. Diversity combines both.
- Simpson's index D = 1 minus the sum of (n/N)². A higher D means greater diversity for the same sampling method.
- Threats include habitat loss and fragmentation, invasive species, overexploitation, pollution and climate change; habitat loss is usually the greatest proximate threat.
- Conservation can be in situ (protected areas, corridors) or ex situ (seed banks, captive breeding). Both have trade-offs.
- Keystone species have disproportionate influence; flagship species mobilise support; indicator species signal environmental quality.
Worked example
Two plots each have 30 individuals and 3 species. Plot A: 10, 10, 10. Sum of (n/N)² = 3(0.333²) = 0.333; D = 0.667. Plot B: 25, 3, 2. Sum = (0.833² + 0.100² + 0.067²) = 0.694 + 0.010 + 0.004 = 0.708; D = 0.292. Plot A is more diverse despite identical richness, because evenness is higher. Reasoning: richness alone misses dominance; Simpson's index penalises uneven abundance.
Traps
- Saying Plot B is more diverse because it has the same richness; it does not.
- Reversing the Simpson scale: higher D = more diverse.
- Treating a protected area as automatically effective without management or connectivity.
- Confusing ex situ with in situ.
- Assuming all non-native species become invasive; many do not.