Extinction is irreversible. While extinction is a natural process, human impacts have elevated the rate of extinction by at least a thousand, possibly several thousand, times the natural rate.
Habitats are under threat from a variety of human-caused factors including climate change, deforestation, pollution and the introduction of pests and predators.
Loss of habitat, including destruction, degradation and fragmentation, is the primary cause of biodiversity loss. When a species is crowded out of its habitat, or its habitat is destroyed, its numbers will drop until it becomes endangered, in other words threatened with extinction. Extinction is when there is no member of a particular species left alive. Extinction is forever.
Globally there are many thousands of species that are threatened and there are hundreds that are on the verge of extinction.
Whilst extinction happens naturally – over 99% of all species that have existed on earth have become extinct – the rate of extinctions caused by humans has accelerated because of habitat loss.
Areas under particular threat are those that are most sensitive and prone to pollutants and climate change such as wetlands and tropical rainforests. These ecosystems are also some of the most diverse in earth.
A comprehensive study on extinction risks, conducted at the University of Leeds and published in the magazine Nature in 2004, stated that 15-35% of species in the areas that they studied (that comprise about a fifth of the earth’s land area) could face extinction by 2050.
It might be that certain insects make the most of climate change in the near future. The distribution of some insects has already changed with drastic effects. The bark beetle, for example, has spread into warming Canadian forests and devastated thousands of square kilometres.
New Zealand is a biodiversity ‘hotspot’ – meaning that it has a high number of endemic species. However since human colonisation 50 bird species have gone extinct. Today, invasive species pose the most serious threat to the flora and fauna of New Zealand, but habitat destruction, through deforestation and wetland drainage, is also a major problem.