IB Biology Topic D4.2.2: Requirements for Stability in Ecosystems Notes

Stable Ecosystems Need Energy, Nutrients, Diversity, and a Steady Climate

1. A steady supply of energy keeps productivity going.
2. Continuous nutrient recycling returns carbon, nitrogen, and phosphorus to the ecosystem.
3. High genetic diversity lets populations adapt to disease, climate, and other stresses.
4. Stable climatic conditions keep temperature, rainfall, and humidity within species' tolerance limits.

Energy Flow Sustains Productivity

1. Ecosystems rely on a steady energy supply from the Sun to drive photosynthesis and feed every trophic level.
2. When that supply is cut, productivity falls and the whole ecosystem can lose stability.

Example

• The eruption of Mount Tambora in 1815 cut global sunlight, slowing photosynthesis and causing ecosystem collapses.

Nutrient Cycling Prevents Resource Loss

1. Nutrient cycling keeps carbon, nitrogen, and phosphorus available for life processes.
   1. Decomposers such as fungi and bacteria break down dead matter and return nutrients to the soil or water.
2. An ecosystem stays stable only when nutrients are recycled faster than they are lost.

Genetic Diversity Builds Resilience

1. Populations with high genetic diversity are more resilient to disease, climate change, and other pressures.
   1. Diverse keystone species are especially important, since they hold key ecosystem roles together.

Climate Within Tolerance Limits Keeps Species Alive

1. Ecosystems stay stable when temperature, rainfall, and humidity stay within species' tolerance limits.
   1. A prolonged shift, such as reduced rainfall, can push an ecosystem past those limits toward instability.

Studying Stability Under Controlled Conditions

1. Researchers test how energy flow, nutrient cycling, and diversity affect stability in controlled experimental systems.

Four Threats Can Break Ecosystem Stability

1. Disrupted energy flow: natural events and human activity reduce the energy reaching producers.
2. Nutrient loss: erosion, runoff, and land clearing strip nutrients out of the system.
3. Loss of genetic diversity: habitat destruction, overexploitation, and disease weaken populations' resilience.
4. Climate change: rising temperatures and shifting rainfall push conditions beyond tolerance limits.

Example

• Coral bleaching from rising sea temperatures disrupts marine biodiversity.