IB Biology Topic D4.2.6: Assessing Sustainability of Resource Harvesting from Natural Ecosystems Notes

Sustainable Harvesting Keeps Extraction At or Below Regeneration

1. Harvesting is sustainable only when the rate of extraction does not exceed the rate of natural replacement.
2. Keeping this balance preserves ecosystems for future generations.

Three Principles Decide Whether Harvesting Is Sustainable

1. Rate of replacement
   1. Resources must regenerate at a rate that matches or exceeds harvesting.
2. Ecosystem health
   1. Harvesting should not disrupt nutrient cycles, energy flow, or biodiversity.
3. Long-term perspective
   1. Decisions must consider the needs of future generations.

Sustainable Plant Harvesting Manages Growth and Replenishment

1. Sustainable plant harvesting manages growth rates and replenishes what is taken.
2. Enough seeds and young trees must remain for the population to regenerate.

Case study

• Brazil nut harvesting
• Brazil nuts from Bertholletia excelsa depend on healthy forests for regeneration.
• Overharvesting and logging threaten young tree populations, making the practice unsustainable in some areas.
• Leaving seeds to germinate keeps enough remaining to grow new trees.
• Protecting young trees means avoiding harvest where seedlings are sparse.

Sustainable Fish Harvesting Prevents Overfishing and Depletion

1. Marine ecosystems need careful management to prevent species depletion.
2. Catch limits must be tied to how fast a population can recover.

Case study

• Atlantic cod (Gadus morhua)
• Atlantic cod populations collapsed in the 20th century due to overfishing, showing why sustainable practices matter.
• Monitoring populations uses surveys to estimate population sizes and reproductive rates.
• Fishing quotas limit the catch so it aligns with recovery rates.
• Protected no-fishing zones support breeding and replenishment.

Maximum Sustainable Yield Sits at the Steepest Point of the Growth Curve

1. The sigmoid growth curve (logistic growth curve) helps scientists find sustainable harvest levels.
2. Maximum Sustainable Yield (MSY) is the highest harvest rate that does not deplete the population.
3. MSY sits at the midpoint of the curve, around half the carrying capacity, where the population growth rate is fastest.

Three Challenges Meet Three Practical Solutions

1. Data uncertainty
   1. Inaccurate or incomplete data on population dynamics can lead to overharvesting.
   2. Solution: use adaptive management, where strategies change as new data arrives.
2. Economic pressure
   1. Demand for resources often pushes people toward unsustainable practices.
   2. Solution: promote alternative livelihoods and offer incentives for sustainable use.
3. Climate change
   1. Rising temperatures and shifting conditions disrupt resource availability.
   2. Solution: build climate projections into management plans.