📌Definition Table

Term	Definition
Habitat Loss	The destruction, fragmentation, or degradation of natural habitats, reducing their ability to support species.
Overexploitation	The unsustainable harvesting of species for food, trade, or other purposes.
Invasive Species	Non-native species that outcompete, prey on, or otherwise harm native species and ecosystems.
Pollution	The introduction of harmful substances or energy into the environment, adversely affecting biodiversity.
Climate Change	Long-term alteration of global or regional climate patterns, impacting ecosystems and species survival.

📌Introduction

Biodiversity faces unprecedented threats from human activities, leading to what many scientists call the sixth mass extinction. These threats operate at multiple scales — from local habitat destruction to global climate change — and often act synergistically, accelerating biodiversity loss. Understanding these threats is essential for developing effective conservation strategies and policies to protect life on Earth.

📌 Habitat Loss and Fragmentation

• Caused by agriculture, urbanisation, mining, and infrastructure development.
• Leads to smaller, isolated populations more vulnerable to extinction.
• Reduces available food, shelter, and breeding sites.
• Alters ecological processes such as pollination and nutrient cycling.
• Creates edge effects that change microclimates and species interactions.
• Particularly devastating for species with large home ranges or specialised habitats.

🧠 Examiner Tip: Always specify the driver behind habitat loss in examples — e.g., deforestation for soybean farming in the Amazon.

📌 Overexploitation

• Includes overfishing, overhunting, and overharvesting of plants.
• Depletes populations faster than they can reproduce.
• Can cause collapse of fisheries and wildlife populations.
• Often driven by high market demand and illegal trade.
• Selective harvesting can alter genetic diversity.
• Example: overharvesting of medicinal plants leading to extinction risk.

🧬 IA Tips & Guidance: An IA could assess the impact of human harvesting on population sizes of a local plant or animal species.

📌 Invasive Species

• Outcompete native species for resources.
• May introduce diseases to which natives have no immunity.
• Can alter ecosystem structure and function.
• Often spread through global trade and travel.
• Particularly harmful to island ecosystems.
• Example: introduction of brown tree snakes to Guam leading to bird extinctions.

🌐 EE Focus: An EE could investigate the ecological and economic impacts of a specific invasive species in a local area.

📌 Pollution

• Chemical: pesticides, heavy metals, and industrial waste harming organisms directly.
• Plastic: ingestion and entanglement affecting marine life.
• Nutrient: fertiliser runoff causing eutrophication and dead zones.
• Light and noise: disrupting animal behaviours such as migration and reproduction.
• Pollution can act synergistically with other threats.
• Persistent pollutants can bioaccumulate in food chains.

❤️ CAS Link: A CAS project could involve organising a community clean-up and awareness campaign on pollution impacts on biodiversity.

📌 Climate Change

• Alters temperature and precipitation patterns.
• Shifts species ranges and disrupts migration timing.
• Causes coral bleaching and loss of polar ice habitats.
• Increases frequency of extreme weather events.
• Forces rapid adaptation or migration, which many species cannot achieve.
• Contributes to ocean acidification, harming marine biodiversity.

🔍 TOK Perspective: Decisions on prioritising biodiversity threats involve value judgments, as resources are limited and trade-offs must be made between economic and environmental goals.

📝 Paper 2:
Expect to discuss major threats to biodiversity, give examples, and explain how these threats interact to accelerate species loss.