IB DP Biology Stability and change Study Notes
IB DP Biology Stability and change Study Notes
IB DP Biology Stability and change Study Notes at IITian Academy focus on specific topic and type of questions asked in actual exam. Study Notes focus on IB Biology syllabus with guiding questions of
- What features of ecosystems allow stability over unlimited time periods?
- What changes caused by humans threaten the stability of ecosystems?
Standard level and higher level: 4 hours
Additional higher level: 2 hours
D4.2.1—Stability as a property of natural ecosystems
Key Points:
- Stability: An ecosystem is considered stable if it can persist indefinitely due to the mechanisms operating within it.
- Examples of Stable Ecosystems:
- The Daintree Rainforest in Australia, estimated to be 180 million years old, contains species from ancient plant families, highlighting its long-term stability.
- The Borneo Lowland Rainforest, though facing recent losses, has existed for about 140 million years.
- The Namib Desert in Southern Africa, with its unique adaptations to arid conditions, has remained relatively intact and stable for an estimated 55-80 million years.
Fragility of Ecosystem Stability:
- While these examples demonstrate long-term stability, it’s crucial to remember that the mechanisms sustaining ecosystems are fragile.
- Even seemingly minor perturbations can disrupt the balance and cause changes within the ecosystem.
In essence, the image emphasizes that while some ecosystems have shown remarkable resilience over long periods, their stability is not guaranteed and can be easily compromised by various factors.
D4.2.2—Requirements for stability in ecosystems
There must be a steady supply of energy entering the system and nutrient cycles should not have significant leakages, meaning nutrients should remain within the ecosystem. Secondly, individual species, especially keystone species, must have high genetic diversity. This diversity allows populations to adapt and survive environmental selection pressures.
Several types of environmental change can disrupt ecosystem stability. Harvesting and removal of materials from the environment can disrupt nutrient cycles. Erosion can result in the loss of nutrients. Eutrophication, the nutrient enrichment of a body of water, can cause imbalances in the ecosystem. Selective removal of species, such as through epidemics or poaching, can also disrupt ecosystem structure, particularly if a keystone species is removed.
If the genetic diversity of a population drops below a certain threshold, it becomes less resilient. High biodiversity tends to be associated with stable ecosystems because it provides a robust community structure.
The relationship between climate and ecosystem type is crucial. For example, high rainfall allows for the development of forests, while moderate rainfall supports grasslands. Prolonged changes in precipitation due to climate change can cause ecosystem disruption. There are concerns that changes in rainfall patterns could lead to a tipping point in the Amazon rainforest, causing it to transition from forest to grassland.