Biodiversity of New Zealand - Human Impact

Human Impact

The arrival of humans in New Zealand has presented a challenge for the native species, causing the extinction of several. This is predominantly because many species in New Zealand have evolved in the absence of mammalian predators for the last few million years (a situation known as ecological naivety), thus losing the responses needed to deal with such threats. Humans brought with them to New Zealand (intentionally or otherwise) a host of attendant species, starting with the Polynesian Rat, and now including stoats, weasels, Black Rats, Norway Rats, Brushtailed Possums, and feral cats and dogs, as well as herbivores such as deer, wallabies and tahr (a wild goat species from the Himalayas), which detrimentally affect native vegetation.

The date of the first arrival of the Māori in New Zealand is given as around 1300 CE, but some recent evidence suggests that Polynesian travellers arrived earlier, as Polynesian Rats seemed to have arrived in 500 CE. Their arrival set off a first wave of extinctions, eliminating smaller defenceless ground nesting birds such as the New Zealand Owlet-nightjar. A second wave of extinctions was triggered by the arrival of the Māori, who hunted many of the larger species, such as the moa, adzebill and several large ducks and geese, for food. The Harpagornis and Eyles's Harrier are thought to have gone extinct due to the loss of their food source. A third wave of extinction began with the arrival of European settlers, who brought with them numerous new mammal species, particularly the predatory domestic cat, and initiated more habitat modification. In all, over 50% of New Zealand's bird species are considered extinct, along with a species of bat and several frogs, a freshwater fish (the New Zealand greyling), skinks and geckos; this is second only to Hawaii in terms of proportion of species lost.

In some instances, the extinction of New Zealand's native fauna has brought about a natural colonisation from Australia. In the case of the Silvereye, which colonised New Zealand in the 19th century, it had no relative in New Zealand's original fauna and is now restricted to newer man-made niches. In the case of the Black Swan (which was originally thought to have been introduced by humans but is now suspected to have self-introduced), the invading species re-occupied part of its former range (the extinct New Zealand Swan is now believed to be a subspecies of the Black Swan). The arrival of the Pukeko and the Swamp Harrier is more interesting, mirroring the arrival of the same two species in the past, before they evolved into the Takahe and the Eyles's Harrier. Once these specialised birds declined and (in the case of the harrier) went extinct, their niches were available and colonisation could occur again.