Rucete ✏ Campbell Biology In a Nutshell
Unit 8 ECOLOGY — Concept 56.1 Human Activities Threaten Earth’s Biodiversity
Biodiversity is declining at an unprecedented rate due to human activities. Conservation biology aims to understand and reverse this loss by studying genetic, species, and ecosystem diversity, while addressing the four major threats: habitat loss, introduced species, overharvesting, and global environmental change.
1. Levels of Biodiversity
- Genetic diversity: variation within and between populations; loss reduces adaptive potential
- Species diversity: number and abundance of species; ~1.8 million known, up to 100 million estimated
- Ecosystem diversity: variety of ecosystems; loss impacts entire ecological networks
2. Why Biodiversity Matters
- Biophilia: innate human love for nature
- Ethical belief in species' right to exist
- Future generations: ensures stable ecosystems and resources
- Practical benefits:
- Medicines: rosy periwinkle → cancer drugs
- Agriculture: virus-resistant wild rice
- Industry: Taq polymerase from Yellowstone bacteria
- Ecosystem services: pollination, water purification, nutrient cycling
3. Four Major Threats to Biodiversity
① Habitat Loss
- Biggest global threat
- Caused by agriculture, development, logging, mining, climate change
- Examples:
- 98% of Central America’s dry forest gone
- 70% of coral reefs damaged
- Mobile River dams → 40+ mollusk extinctions
- Fragmentation isolates small populations
② Introduced Species
- Also known as invasive, exotic, non-native
- Free from native predators, they outcompete or eat local species
- Examples:
- Brown tree snake on Guam: 12 bird and 6 lizard extinctions
- Zebra mussels in Great Lakes: ecosystem and infrastructure damage
- Kudzu and European starlings displace natives in the U.S.
- Responsible for ~40% of extinctions since 1750
③ Overharvesting
- Extraction rate exceeds population recovery
- High-risk species: limited range or low reproduction
- Examples:
- Great auk: hunted to extinction
- African elephants: poached for ivory
- Bluefin tuna: <20% of 1980 levels due to sushi demand
- DNA tools help trace poaching and guide conservation
④ Global Environmental Change
- Changes climate, chemistry, and Earth's support systems
- Examples:
- Acid precipitation (pH < 5.2): damages lakes, soil, forests
- U.S. sulfur emissions cut 75% since 1990, but ecosystem recovery is slow
- Broader changes (climate, ozone, CO₂) covered in Concept 56.4
4. Can Extinct Species Be Resurrected?
- Cloning: Pyrenean ibex clone lived 7 minutes
- Hybrid embryos from northern white rhino sperm and southern rhino eggs
- Still, habitat conservation is more effective than revival
In a Nutshell
Biodiversity is vital for ecological stability, human well-being, and future innovation. Yet habitat destruction, invasive species, overexploitation, and global change are driving extinctions at a rate far beyond the natural background. Conservation biology seeks to understand, prevent, and reverse this crisis, not only for wildlife but for the survival of humanity itself.