Introduced species in New Zealand ? Their impacts on a biodiversity hotspot

The issue of naturalization of introduced species to New Zealand was raised in an article in Nature (Ritchie 1922a Thompson 1922) 88 years ago. Here, we take the opportunity to assess the impacts of introduced species to the islands of New Zealand, one of the only entire countries, such as Madagascar, Japan, Philippines and New Caledonia to be described as a biodiversity hotspot (Reid 1998; Abbitt et al. 2000; Smith et al. 2001; Mittermeier et al. 2004). Between 1769 and 1919, 1170 species were recorded as being introduced to New Zealand (Thompson 1922) (Table 1). Ritchie (1922) reviewed the publication of Thompson?s inventory and warned against the introduction of exotic species without proper planning and assessment of the impacts on the existing biota. The warning was given because of New Zealand?s biodiversity had evolved in the absence of mammalian predators. Many bird, reptile and invertebrate species had limited defences against mammal species such as rats Rattus spp, mustelids (Stoat Mustela erminea, Ferret Mustela furo and Weasel Mustela nivalis vulgari), Brushtail Possum Trichosurus vulpectula and Cat Felis cattus. At the beginning of the 20th century, most of New Zealand?s large land vertebrates were extinct or threatened with extinction. The rapid expansion of mustelids, rats and Cat had caused considerable contractions in the distribution of large ground birds such as Kakapo Strigops habroptilus, South Island Takahe Porphyrio mantelli hochstetteri and species of waterfowl.