The Five Major Threats to Biodiversity

Research and global reports consistently identify the following as the primary causes of species loss:

• Habitat Destruction: The conversion of forests, wetlands, and other ecosystems for agriculture, urban development, and infrastructure is the leading cause of biodiversity decline worldwide12457.

• Overexploitation: Unsustainable hunting, fishing, and harvesting of plants and animals put immense pressure on wild populations, often pushing them toward extinction12567.

• Alien (Invasive) Species: The introduction of non-native species can disrupt local ecosystems, outcompete native species, and cause extinctions, especially on islands and isolated habitats1267.

• Pollution: Contaminants from industrial, agricultural, and urban sources degrade habitats and directly harm species, contributing significantly to biodiversity loss12567.

• Climate Change: Although not listed in your options, climate change is also widely recognized as a growing threat to biodiversity1267.

Evaluating the Options

Let’s review each option in the context of major threats:

• Habitat destruction (Option 1): Universally recognized as the top threat to biodiversity12457.

• Overexploitation (Option 2): A major driver of species loss, including overhunting, overfishing, and excessive resource extraction12567.

• Alien invasion (Option 3): Refers to the introduction of invasive species, a leading cause of extinctions, especially in sensitive ecosystems1267.

• Pollution (Option 4): A significant global threat, impacting species and ecosystems through toxic substances and habitat degradation12567.

Conclusion: All Are Major Threats

All four options—habitat destruction, overexploitation, alien invasion, and pollution—are considered major threats to species diversity by global authorities like the IUCN, WWF, and IPBES12567. None of these can be excluded from the list of primary drivers behind biodiversity loss.

However, if you are seeking the least emphasized among the four in some specific contexts, pollution is sometimes ranked slightly lower compared to habitat destruction, overexploitation, and invasive species, but it is still a major threat globally.

Correct answer:
None of the options listed is not a major threat; all are considered significant drivers of species diversity loss. If required to choose, pollution is sometimes considered less direct than the others, but it remains a major threat.