Q.Explain the "Evil Quartet" of biodiversity loss.

[!TLDR] The Evil Quartet is the four main causes of biodiversity loss: habitat loss, over-exploitation, alien species invasion, and co-extinction. …

[!ANSWER] The Evil Quartet is the name given to the four major, human-driven causes of biodiversity loss.

1. Habitat loss and fragmentation — the outright destruction of natural habitat for agriculture, urban development, or infrastructure, or its division into smaller, isolated patches. This reduces the total habitat area available to a species and can prevent populations in separate fragments from interbreeding, weakening their long-term genetic health.
2. Over-exploitation — the harvesting of a species (through hunting, fishing, logging, or collection) at a rate faster than its population can naturally replace itself, which has historically driven numerous species to extinction or to the brink of it.
3. Alien species invasion — the introduction of a non-native species into an ecosystem, whether deliberate or accidental, where it can prey upon, outcompete, or introduce new diseases to native species that have no evolved defences against it (e.g. the Nile perch's introduction into Lake Victoria, which devastated the lake's native cichlid fish diversity). …

• Naming only two or three of the four causes and forgetting co-extinction, which is the least intuitive of the four. …