8.6 Biodiversity
- Syllabus
- 2025
- Topic
- 8.6
- Level
- —
Learning objectives
8.6A—Describe the relationship between ecosystem diversity and its resilience to changes in the environmentDescribe the relationship between ecosystem diversity and its resilience to changes in the environment.• Natural and artificial ecosystems with fewer component parts, and with little diversity among the parts, are often less resilient to changes in the environment.• Keystone species, producers, and essential abiotic and biotic factors contribute to maintaining the diversity of an ecosystem.8.6B—Explain how the addition or removal of any component of an ecosystem will affect its overall short-term and…Explain how the addition or removal of any component of an ecosystem will affect its overall short-term and longterm structure.• The effects of keystone species on the ecosystem are disproportionate relative to their abundance in the ecosystem. When they are removed from the ecosystem, it often collapses.
Why Biodiversity Supports Ecosystem Resilience
Ecosystem resilience is the capacity to withstand environmental change or recover after disturbance. Natural or artificial ecosystems with fewer component parts and little diversity among those parts are often less resilient.
With more varied components and interactions, an environmental pressure is less likely to disrupt every pathway in the same way. Other populations or processes may continue to support energy flow and matter cycling while affected parts recover.
| Component | Contribution to maintained diversity |
|---|---|
| Producers | Capture energy and support food-web energy entry |
| Keystone species | Maintain interactions or population patterns despite sometimes low abundance |
| Essential biotic factors | Supply living interactions such as feeding, decomposition, or symbiosis |
| Essential abiotic factors | Provide physical or chemical conditions and resources required by organisms |
If a low-diversity system depends strongly on only a few components, damage to one can remove a large fraction of its functioning. A more diverse system is often more likely to retain some functioning and recover.
Greater diversity does not make an ecosystem immune to disturbance. The CED relationship is probabilistic: low-diversity systems are often less resilient, not always certain to collapse.
How Ecosystem Changes Cascade Over Time
Adding or removing an ecosystem component changes its interactions with other biotic or abiotic components. Direct effects can appear quickly, while indirect effects spread through food webs and resource pathways over longer periods.
| Time scale | Typical reasoning |
|---|---|
| Short term | Populations directly using, consuming, competing with, or being consumed by the changed component respond first |
| Long term | Altered abundances change further interactions, energy flow, nutrient availability, diversity, and overall community structure |
A keystone species has an ecosystem effect that is disproportionately large relative to its abundance. Its importance comes from the interactions it controls, not from being the most numerous species.
Keystone species removed → directly connected populations change → effects propagate to other trophic levels or resources → biodiversity and stability decline → ecosystem structure may collapse.
The same causal method applies to an addition or restoration: identify the new direct interaction, predict which populations change first, then trace how those changes alter later energy, matter, and food-web relationships.
Low abundance does not mean low ecological importance. Conversely, not every added or removed species is a keystone species, so the magnitude of change depends on its interaction role.