Categories of Biodiversity

Biodiversity is formally defined as the variability among living organisms from all sources, including terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part. This includes diversity within species, between species and of ecosystems (Convention on Biological Diversity, 1992).

Three Levels of Biodiversity

1. Genetic Diversity

Genetic diversity refers to the total variation in genetic information (DNA) within and among populations of the same species.

• Measured through allele frequency, heterozygosity, and number of polymorphic loci
• A population with high genetic diversity has many different alleles for each gene
• Underpins a species’ ability to adapt to environmental change
• Reduced by inbreeding, genetic drift and population bottlenecks

Example: The cheetah (Acinonyx jubatus) has extremely low genetic diversity due to a past population bottleneck, making the species vulnerable to disease and environmental stress.

2. Species Diversity

Species diversity describes the number and relative abundance of species in a given area or community.

Two main components:
| Component | Definition |
|—|—|
| Species richness | Total number of species present |
| Species evenness | How equally individuals are distributed among species |

High richness + high evenness = high species diversity. Tools like Simpson’s Index of Diversity (SID) combine both components into a single measure.

Example: A rainforest may have hundreds of tree species in one hectare, while a monoculture wheat field has one. The rainforest has far greater species diversity.

3. Ecosystem Diversity

Ecosystem diversity refers to the variety of habitats, biological communities and ecological processes occurring in the biosphere.

• Encompasses structural diversity (e.g. vertical layering in forests)
• Functional diversity (e.g. presence of decomposers, pollinators, predators)
• Diversity of biomes globally: tropical rainforests, coral reefs, wetlands, deserts, grasslands

Example: Victoria contains over 60 distinct bioregions including alpine ash forests, coastal heathlands and mallee scrublands — each supporting different suites of species.

Interconnections Between Levels

The three levels are not independent:

Genetic diversity → enables adaptation → supports species persistence
      ↓
Species diversity → drives ecosystem function → sustains ecosystem diversity
      ↓
Ecosystem diversity → provides varied habitats → maintains genetic variation

Loss at one level weakens the others. For instance, habitat fragmentation (reduced ecosystem diversity) isolates populations, leading to inbreeding (reduced genetic diversity) and local extinctions (reduced species diversity).

Why Categorising Biodiversity Matters for Management

Different conservation strategies target different levels:
- Genetic level: Gene banks, captive breeding, managed translocation
- Species level: Protected area designation, threatened species listings
- Ecosystem level: Landscape-scale conservation corridors, revegetation

EXAM TIP: VCAA questions often ask you to distinguish between the three categories with specific examples. Always link genetic diversity to evolutionary potential and species resilience, not just to number of alleles.