Biodiversity loss has been most pronounced on islands and in specific locations around the tropics, where distinctive species often evolve in isolation from the rest of the world. The introduction of alien species along with hunting and the clearing of vegetation by humans on small, isolated islands account for around 80% of known extinctions. Wider problems such as climate change, pollution, over-exploitation, and land use change - often to make way for agriculture - are causing biodiversity to decline in other areas such as in the oceans and rainforests.
While much species loss has taken place in specific locations, it is often driven by global systems, with choices and actions taken in one place having effects far away.
One recent analysis found that approximately 60% of total global biodiversity loss for bird and mammal species has occurred in just seven countries between 1996 and 2008 – Indonesia, Malaysia, Papua New Guinea, China, India, Australia and the USA, where the majority has occurred on the islands of Hawaii.
Due to their relative isolation, islands tend to be home to wide varieties of unique species and habitats, often making them biodiversity hotspots. The limited habitats that species have on islands, however, makes them exceptionally vulnerable. Foreign species introduced to an island either accidentally or deliberately by humans can quickly out compete or directly destroy native populations. In Hawaii and most other tropical islands, for example, foreign species such as rats, feral cats, pigs, goats and non-native plants have decimated the local flora and fauna, which have not evolved to cope with the pressure from these introduced species.
Biodiversity loss also affects larger islands. On Madagascar, for example, deforestation, mining and climate change are causing significant habitat loss and threatening native species. Similarly, Australia lost 5-10% of its biodiversity between 1996 and 2008 while high levels of deforestation to make way for agricultural plantations have particularly affected the species rich rainforests of Indonesia.
In the past 20 years extinctions have also become common on continents. Most threatened species can be found in areas where large human populations are concentrated, such as southeast China and the Western Ghats of India. According to the World Wildlife Fund's Living Planet Report 2020, Latin America and the Caribbean have suffered notably high losses of amphibians, reptiles and fish due to a combination of threats including disease, habitat loss and over-exploitation.
Biodiversity loss, however, is not just confined to the land. Life in the oceans is being threatened by overfishing, habitat degradation, pollution, and acidification due to rising carbon dioxide levels in the sea water. Corals, for example, have undergone dramatic declines since the mid-1990s.
For more on this topic Past and future decline and extinction of species | Royal Society
Climate change and biodiversity
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