The Sixth Mass Extinction is Driven by Humans
- At the core of the biodiversity crisis is the exponential growth of the human population, now nearing 8 billion, up from less than 2 billion in 1920.
- This growth amplifies:
- Demand for resources (e.g., food, water, and energy).
- Space consumption, leading to urban sprawl and deforestation.
- Industrial activity, which depletes ecosystems and accelerates pollution.
Although population growth itself is neutral, its associated activities amplify specific threats to biodiversity.
Direct Causes of Biodiversity Loss
1. Over-Exploitation: Unsustainable Use of Resources
- Hunting and fishing: Species such as the Atlantic bluefin tuna and the African elephant face drastic declines due to overfishing and poaching.
- Deforestation for timber: Over-harvesting of keystone tree species disrupts forest ecosystems, threatening dependent species.
- Medicinal and ornamental plant trade: Unsustainable harvesting leads to population declines of species like wild orchids.
Many students mistakenly believe that only large-scale commercial activities threaten biodiversity. In reality, even small-scale, unsustainable practices can have devastating effects when repeated over time.
2. Habitat Loss: Urbanization and Agriculture
- Urbanization: Since 1992, urban areas have doubled, replacing natural habitats with cities and infrastructure.
- Agricultural expansion: Over 13 billion hectares of forests and wetlands have been converted into farmland.
The Amazon rainforest, home to immense biodiversity, is being cleared for soy and cattle farming.
TipWhen studying habitat loss, remember that it often leads to "edge effects," where the remaining habitat becomes fragmented and less suitable for species that require large, continuous areas.
3. Pollution is A Hidden Threat
- Pesticides and fertilizers: Eutrophication from agricultural runoff creates dead zones in water bodies.
- Plastic pollution: Microplastics harm marine life by causing ingestion of toxins, bioaccumulation, and physical injury.
The Gulf of Mexico has a hypoxic zone due to excessive nutrient pollution.
4. Invasive Alien Species
- Globalization has introduced species to ecosystems where they outcompete or prey on native species.
- Think diseases and viruses.
- Black bass introduced into Guatemala’s Lago de Atitlán led to the extinction of the endemic Atitlán grebe.
- Pathogens like chytrid fungus have devastated amphibian populations globally.
Think of an invasive species as an uninvited guest at a party who eats all the food, leaving none for the hosts. Similarly, invasive species consume resources or prey on native species, disrupting the balance of ecosystems.
5. Water Diversion and Land Use Changes
- Dams and irrigation systems alter ecosystems.
- This leads to the loss of wetlands and aquatic habitats.
- Many students mistakenly believe that only large-scale commercial activities threaten biodiversity.
- In reality, even small-scale, unsustainable practices can have devastating effects when repeated over time.
The Aral Sea shrank drastically due to water diversion for agriculture, causing ecosystem collapse.
The Compound Impact of Climate Change
- Though not the sole focus here, climate change exacerbates all other threats:
- Habitat shifts: Arctic foxes lose territory to encroaching red foxes due to warming.
- Ocean acidification: Coral bleaching disrupts marine ecosystems.
- How do cultural and economic values influence decisions about which species or ecosystems to prioritize for conservation?
- Should humans take responsibility for reversing all the damage they have caused?
- What are the five main causes of the biodiversity crisis?
- Can you explain how human population growth exacerbates each of these causes?
