Human activities threaten biodiversity by destroying or fragmenting habitats, introducing invasive species, and releasing pollutants. These pressures reduce genetic, species, and habitat diversity and can interact, making ecosystems less resilient.
The Reasoning and Mechanisms
This is core IB ESS Subtopic 3.2: Human impact on biodiversity, studied at SL and HL. Biodiversity includes genetic, species, and habitat diversity.
| Human activity | Mechanism reducing biodiversity | Named example |
|---|---|---|
| Habitat loss and fragmentation | Agriculture, urbanization, mining, and deforestation remove habitats. Fragmentation isolates populations, restricts breeding, and creates small populations vulnerable to local extinction. | Brazilian Amazon deforestation replaces rainforest with pasture, cropland, roads, and settlements. |
| Invasive alien species | Humans move organisms beyond natural ranges. Without normal predators or competitors, they may spread through competition, predation, disease, or parasitism. | Brown tree snakes introduced to Guam caused declines and local extinctions of native forest birds. |
| Pollution | Pesticides, plastics, sewage, excess nutrients, and toxic metals can kill organisms, disrupt reproduction, alter habitats, or accumulate through food chains. Sensitive species disappear first, reducing richness and evenness. | Nutrient pollution drives eutrophication and seasonal hypoxia in the Gulf of Mexico. |
These pressures rarely operate independently. Habitat fragmentation can reduce a native population's resilience, while pollution or an invasive predator adds stress and pushes the ecosystem toward a tipping point.
A common misconception is that biodiversity means only the number of species. Species diversity depends on both richness and evenness; biodiversity also includes genetic and habitat diversity.
Conservation also involves perspectives and environmental justice. Protected areas may conserve habitats but disadvantage local or Indigenous communities through inequitable access and decision-making, especially at HL.
Exam Technique
For an explain question, identify the activity, describe its mechanism, and link it explicitly to reduced biodiversity. Use a named example; stronger responses explain interactions, resilience, and tipping points.
