Biodiversity is the variety of life in all its forms, levels and combinations. In IB Biology, it includes genetic diversity, species diversity and ecosystem diversity; this content applies to both SL and HL.
The Three Levels of Biodiversity
Biodiversity is measured at several connected levels rather than by counting species alone.
| Level | Meaning and example |
|---|---|
| Genetic diversity | Variation in genes and alleles among individuals within a species. For example, different alleles within a crop population may produce variation in disease resistance. |
| Species diversity | The variety of species in a habitat or ecosystem. A coral reef containing many species has greater species diversity than a habitat containing very few species. |
| Ecosystem diversity | The variety of ecosystems, habitats and biological communities across an area. Forests, wetlands, grasslands and coral reefs represent different ecosystems. |
These levels are interconnected. Genetic variation produces differences among individuals and provides the variation on which natural selection acts. Different species interact through relationships such as predation, competition and mutualism, while different ecosystems support distinct communities under different abiotic conditions.
A common misconception is that biodiversity means only the number of species present. Species richness is relevant, but the IB definition is broader: two areas may contain similar numbers of species while differing substantially in genetic or ecosystem diversity.
Biodiversity can be reduced by anthropogenic causes such as habitat loss, over-exploitation, pollution, invasive alien species and climate change. Conservation therefore requires several approaches, including in situ conservation in natural habitats, ecosystem restoration and ex situ conservation in zoos, botanic gardens or seed banks.
Exam Technique
For a define question, state: “Biodiversity is the variety of life in all its forms, levels and combinations, including genetic, species and ecosystem diversity.” For an question, develop linked cause-and-effect statements rather than merely listing threats or conservation methods. Avoid defining biodiversity as “the number of organisms,” because abundance and biodiversity are not the same concept.