MYP Biology Overexploitation Notes

What Is Overexploitation?

1. Overexploitation is a predictable outcome when renewal cannot keep up with use.
2. When extraction exceeds the population’s natural growth rate, numbers decline and may reach a point where recovery is impossible.
3. Overexploitation affects fish stocks, forests, wildlife, and any population that depends on natural renewal.

Why Do Humans Overuse Shared Resources?

1. Overexploitation often occurs even when people understand the long-term damage, because short-term benefits feel more important.
2. This pattern is explained by the tragedy of the commons.

The Tragedy of the Commons

1. Commons are shared resources: oceans, forests, rangelands, the atmosphere.
2. Because no one owns them, individuals maximize personal gain even when it harms the collective resource.
3. Drivers of overuse include:
   1. Pursuit of immediate economic gain
   2. Lack of regulation or unclear ownership
   3. Population growth increasing consumption
   4. Technology enabling faster extraction
   5. Limited incentives to conserve shared resources
4. These pressures explain rapid declines in global fisheries, forests, and wildlife.

What Happens When Populations Are Overharvested?

A population collapses when its numbers fall so low that normal reproduction cannot rebuild it, even if harvesting stops.

Population collapse

1. Collapse occurs when a population drops below its minimum viable population (MVP).
2. Below this threshold, survival is unlikely.
3. Reasons include:
   1. Reduced birth rates: too few adults remain to reproduce.
   2. Disrupted age structure: removal of mature adults removes reproductive capacity.
   3. Difficulty finding mates: low density reduces successful reproduction.
   4. Loss of genetic diversity: increases inbreeding and reduces adaptability.
   5. Ecological time lags: species may take decades to recover, or never recover.

What Are the Consequences of Overexploitation?

Grouping consequences more explicitly by system type makes this easier for you to study:

1. Ecological consequences:
   1. Extinctions
   2. Disrupted food webs
   3. Loss of keystone species
   4. Shifts to new ecosystem states
   5. Increase in invasive or opportunistic species
2. Social and economic consequences:
   1. Loss of livelihoods for dependent communities
   2. Collapse of industries (e.g., fisheries, timber)
3. Food insecurity
   1. Long-term economic instability
   2. Loss of cultural practices tied to natural resources

Why Is Recovery After Collapse So Difficult?

1. Once a population falls below its MVP, the mechanisms that normally support recovery no longer function effectively.
2. There are several barriers to this:
   1. Low Density: individuals cannot easily find mates, reducing reproduction.
   2. Genetic Bottlenecks: small populations lose genetic diversity, weakening adaptability and resilience.
   3. Altered Ecosystems: even if harvesting stops, the ecosystem may have shifted to a new stable state that no longer supports the species.
   4. Slow Reproduction: long-lived species with low reproductive rates take decades to rebuild.
   5. Continued Pressures: Illegal harvesting, habitat change, or climate shifts may persist despite legal protections.

How Can Overexploitation Be Prevented?

1. Preventing overexploitation requires keeping population use within natural limits so renewal can keep pace with removal.
2. Some key principles of this are:
   1. Harvest rates must not exceed renewal rates, meaning populations must stay above their MVP.
   2. Age structure must be preserved, especially breeding adults.
   3. Monitoring must be accurate and continuous.
   4. Shared resources require international cooperation.