Stability of natural ecosystemsSpec D4.2.1, D4.2.2
In short
Stability is a property of natural ecosystems: they can keep the same structure and functions over long periods, sometimes millions of years. Stability requires a supply of energy, recycling of nutrients, genetic diversity, and climatic variables remaining within tolerance levels. If one requirement fails, the ecosystem may change to a different state.
A stable ecosystem keeps a similar community and similar processes over time, and recovers after disturbance. Stability is a property of natural ecosystems. There is evidence, from fossils and from pollen preserved in sediments, that some ecosystems have persisted for millions of years.
- Tropical rainforest in the Daintree region of north-east Australia descends from forests that covered much of Gondwana. Fossil pollen shows rainforest in Australia for tens of millions of years, and it survived here while drier climates shrank it elsewhere. (Popular figures of 135–180 million years are not firmly supported.)
- The Namib Desert in south-west Africa has been arid or semi-arid for at least 55 million years, and extremely dry for the last few million. Many desert species there, such as fog-basking beetles, are found nowhere else.
| Requirement | Why it matters |
|---|---|
| Supply of energy | Sunlight captured by producers supports every trophic level; energy is not recycled, so the supply must be continuous. |
| Recycling of nutrients | Decomposers return carbon, nitrogen and phosphorus to the soil and air, so producers never run out. |
| Genetic diversity | Populations with many alleles are more likely to include individuals that survive a new disease or a change in conditions. |
| Climatic variables within tolerance levels | Temperature and rainfall must stay within the range the species can tolerate. |
Linking question: over what timescales do things change in different biological systems? Ecosystems can be stable for millions of years yet collapse within decades once a requirement fails.
Written and checked against the IB Biology HL specification · Updated October 2026