Level: SL and HL: Subtopic 2.1: Individuals, populations, communities and ecosystems
Sustainability is a natural property of ecosystems because their interacting components can maintain long-term viability through energy inputs, nutrient cycling, regulation and recovery from disturbance. However, this does not mean that every ecosystem is permanently stable or immune to human impacts.
How Ecosystems Sustain Themselves
An ecosystem is an open system: energy and matter enter and leave it. Solar energy enters, producers convert it into chemical energy, and energy then flows through food chains before eventually leaving as heat.
Matter behaves differently. Nutrients such as carbon and nitrogen are transferred between organisms, soil, water and the atmosphere through feeding, excretion, death and decomposition. This recycling maintains the resources required for continued biological activity.
| Mechanism | Contribution to sustainability |
|---|---|
| Negative feedback | Counteracts change; for example, increased competition can reduce population growth as carrying capacity is approached. |
| Biodiversity | Provides alternative species and pathways, so one population's decline does not necessarily stop an ecosystem function. |
| Resilience | Allows the ecosystem to tolerate disturbance, avoid a tipping point and recover toward equilibrium. |
| Succession | Replaces one community with another over time, allowing recovery after disturbances such as fire. |
| Nutrient cycling | Returns essential elements to forms that producers can reuse. |
These interactions create an emergent property: ecosystem sustainability results from the whole network rather than from any single organism. In Yellowstone National Park, the restoration of wolves affected herbivore populations and vegetation, illustrating how a keystone species can support wider ecosystem stability.
