Extinction in AP Biology
Extinction is a natural process that has shaped life on Earth for billions of years. It occurs when a species can no longer survive and reproduce in its environment. While some extinctions happen gradually due to natural selection, others result from catastrophic events, leading to mass extinctions. In this guide, we’ll explore the different types of extinction, their causes, and their impact on biodiversity and ecosystems, providing essential knowledge for the AP Biology exam.
1. What Is Extinction?
Extinction occurs when an entire species disappears due to environmental changes, competition, predation, or human activities.
Key Points:
- Natural extinction: Happens at a background rate due to evolutionary changes.
- Mass extinction: A widespread event that wipes out a significant percentage of species.
- Anthropogenic extinction: Human-caused species loss due to habitat destruction, climate change, and pollution.
💡 AP Bio Tip: Extinction plays a key role in natural selection by removing species that cannot adapt to environmental changes.
2. Types of Extinction
A. Background Extinction
Occurs naturally at a low rate due to gradual changes in ecosystems.
Example: The slow decline of species unable to compete for resources.
B. Mass Extinction
A rapid and widespread loss of species caused by global events.
Example: The asteroid impact that led to the extinction of the dinosaurs (Cretaceous-Paleogene event).
C. Human-Induced Extinction
Caused by deforestation, pollution, hunting, and climate change.
Example: The dodo and passenger pigeon went extinct due to overhunting.
💡 AP Exam Tip: Be able to differentiate between background extinction and mass extinction with real-world examples.
3. The Five Major Mass Extinctions
There have been five major mass extinction events in Earth’s history:
- Ordovician-Silurian (440 MYA): Caused by glaciation and sea level changes.
- Devonian (365 MYA): Marine life suffered due to low oxygen levels.
- Permian-Triassic (250 MYA): The largest extinction event, wiping out 90% of species due to volcanic activity.
- Triassic-Jurassic (200 MYA): Allowed dinosaurs to dominate after large-scale species loss.
- Cretaceous-Paleogene (66 MYA): An asteroid impact led to the extinction of the dinosaurs.
💡 AP Bio Tip: The Cretaceous-Paleogene extinction is important because it marks the end of dinosaurs and the rise of mammals.
4. Human Impact on Extinction (The Sixth Mass Extinction)
Scientists believe we are currently experiencing a sixth mass extinction, primarily caused by human activities.
Causes of Human-Induced Extinction:
- Habitat destruction: Deforestation and urbanization.
- Climate change: Global warming alters ecosystems.
- Pollution: Toxins and plastic waste harm species.
- Overexploitation: Overhunting, poaching, and illegal wildlife trade.
💡 Example: The Western Black Rhinoceros was declared extinct due to poaching.
5. Consequences of Extinction on Ecosystems
Extinctions disrupt food webs and ecological balance.
Effects on Biodiversity:
- Loss of keystone species: Can collapse entire ecosystems.
- Reduced genetic diversity: Limits species’ ability to adapt to environmental changes.
- Disruption of ecological services: Pollination, water purification, and climate regulation suffer.
💡 Example: The extinction of bees could threaten global food production.
6. Practice Questions for the AP Biology Test
- What is the difference between background extinction and mass extinction?
- How do human activities contribute to extinction? Provide specific examples.
- Explain the role of extinction in evolution and how it affects biodiversity.
Conclusion: The Role of Extinction in Evolution and Conservation
Extinction is a natural but critical force in evolution and biodiversity. However, human-induced extinctions are occurring at an alarming rate, threatening ecological balance. Understanding extinction causes, mass extinctions, and conservation efforts is essential for both AP Biology and real-world environmental awareness.
More for you about Extinction
Key Areas of Study in Extinction Biology:
- Causes of Extinction:
- Habitat Destruction: The primary driver of modern extinctions, caused by deforestation, urbanization, agriculture, and other human activities.
- Climate Change: Alters ecosystems and habitats, making them unsuitable for many species.
- Overexploitation: Hunting, fishing, and harvesting of species at unsustainable rates.
- Invasive Species: Non-native species that outcompete, prey on, or introduce diseases to native species.
- Pollution: Contaminants that degrade habitats and harm species directly.
- Disease: Emerging pathogens that can decimate vulnerable populations.
- Extinction Dynamics:
- Extinction Debt: The delayed extinction of species due to past habitat loss or environmental changes.
- Population Viability Analysis (PVA): A tool used to predict the likelihood of a species’ extinction based on demographic and environmental factors.
- Trophic Cascades: The ripple effects of extinction through ecosystems, often leading to further biodiversity loss.
- Historical Extinctions:
- Mass Extinctions: Events in Earth’s history where a significant proportion of species died out in a relatively short time (e.g., the Cretaceous-Paleogene extinction that wiped out the dinosaurs).
- Background Extinction: The natural rate of species loss occurring outside of mass extinction events.
- Conservation Strategies:
- Protected Areas: Establishing and managing reserves to safeguard critical habitats.
- Captive Breeding and Reintroduction: Programs to breed endangered species in captivity and release them into the wild.
- Restoration Ecology: Rehabilitating degraded ecosystems to support biodiversity.
- Legislation and Policy: Laws like the Endangered Species Act (ESA) that protect threatened species and their habitats.
- Technological and Scientific Tools:
- Genetic Rescue: Using genetic techniques to increase genetic diversity in small, isolated populations.
- De-extinction: Emerging technologies like cloning and gene editing to potentially revive extinct species.
- Remote Sensing and Monitoring: Using satellite imagery and other tools to track habitat changes and species populations.
- Ethical and Philosophical Considerations:
- Intrinsic vs. Instrumental Value: Debates over whether species have inherent value or are valuable only for their utility to humans.
- Conservation Priorities: Deciding which species or ecosystems to prioritize for conservation efforts.
Importance of Extinction Biology:
- Biodiversity Preservation: Maintaining ecosystem health and resilience by preventing species loss.
- Ecosystem Services: Protecting the benefits that humans derive from ecosystems, such as clean water, pollination, and climate regulation.
- Cultural and Aesthetic Value: Preserving species that hold cultural, spiritual, or aesthetic significance for human societies.
Study AP Biology
Practice Digital SAT
Find us on Facebook