Biodiversity, endemism and human threatsSpec 4.15, 4.16
In short
Biodiversity is the variety of living organisms, which can be considered at the level of habitats, species and genes. Endemic species are found only in one geographical area. Over time evolution has produced an enormous variety of life, but human activities such as habitat destruction, pollution, climate change and overexploitation now threaten it.
- Biodiversity
- The variety of living organisms in a given area or on Earth, measured as the number and abundance of species (species diversity), the genetic variation within species (genetic diversity) and the range of habitats (habitat diversity).
- Endemism
- A species being found in only one geographical region, and nowhere else in the world. Such a species is called endemic. Examples: lemurs in Madagascar; many species on isolated islands such as the Galápagos or Hawaii.
The variety of life over time
Over millions of years evolution by natural selection and speciation has produced an extensive variety of life, with millions of species, most of them not yet described. Biodiversity has been reduced in the past by mass extinctions.
The threat from human activity
The variety of life is now being reduced faster than before, and human activity is the main cause. Endemic species are especially vulnerable because they live in small areas and cannot move elsewhere if their habitat is changed.
| Threat | How it reduces biodiversity |
|---|---|
| Habitat loss and fragmentation | Clearing land for agriculture, housing and roads destroys habitats or divides them into small patches |
| Climate change | Warming changes rainfall and temperature, so species may no longer be adapted to their habitat |
| Pollution | Fertilisers, pesticides and plastics harm organisms or alter habitats |
| Overexploitation | Hunting, fishing and harvesting faster than populations can recover |
| Introduced (invasive) species | Compete with, prey on or bring disease to native species |
Always say how the threat reduces biodiversity (for example "habitat destruction reduces the number of species that can live there"), not only name it.
Written and checked against the Edexcel International A Level Biology (YBI11) specification · Updated October 2026