Loss of Biodiversity

Loss of Biodiversity

Human activity is driving a well-documented, accelerating loss of biodiversity worldwide. Ecologists commonly summarise the four principal, interacting causes of this loss as the "Evil Quartet":

1. Habitat loss and fragmentation — the outright destruction of natural habitat (for agriculture, urbanisation, or infrastructure) or its division into small, isolated patches, which reduces the total area available to a species and can prevent populations in different fragments from interbreeding.
2. Over-exploitation — harvesting a species (through hunting, fishing, or logging) faster than its populations can naturally replace themselves, historically responsible for the extinction or near-extinction of numerous species.
3. Alien species invasion — the deliberate or accidental introduction of a non-native species into an ecosystem, where it may outcompete, prey upon, or bring new diseases to native species that have no evolved defences against it. Well documented examples include the extinction of many native fish species in Africa's Lake Victoria following the introduction of the Nile perch, and the decline of native bird populations on islands after the introduction of predators such as rats and cats, or of foreign plants that displace native vegetation.
4. Co-extinctions — the loss of a species that is bound in an obligate ecological relationship with another species (for example a specific pollinator and the plant it alone pollinates, or a host and its exclusive parasite), so that when one member of the pair goes extinct, the other is inevitably lost as well. …