With its long history of isolation from other land masses, New Zealand has been suggested to be an ‘ark’ for unusual species, such as tuatara and moa. But New Zealand has now been found to be a genetic ark for an introduced species – the stoat.
A recent study reported that stoats in New Zealand harbour genetic variation that has been lost from native populations in Britain. Stoats were introduced to New Zealand in the 1880s and are the biggest threat to our native birds.
Since New Zealand has so many invasive species, I wondered whether we have any other species that are rare in their home countries.
Species introduced to NZ but rare, or extinct, in their native range
An invertebrate example is the short-haired bumblebee. This species was introduced to New Zealand from the United Kingdom over a century ago. In 2000 they were declared extinct in the UK. An unsuccessful attempt was made to re-introduce them from New Zealand, but most of the bees died in quarantine prior to the release. A genetic study of the New Zealand bumblebees showed that they all descend from as few as two individuals. It is possible that this high level of inbreeding contributed to their failure to re-establish. The same study examined DNA from museum specimens of the extinct UK bumblebees and showed that they were genetically similar to those from Sweden. This species has since been re-introduced to Britain from Sweden.
Two botanical examples are radiata pine (Pinus radiata) and macrocarpa (Cupressus macrocarpa), both of which are native to the Californian coast. All of the three remaining wild populations of the endangered radiata pine are threatened by fungal disease (pine pitch canker). Macrocarpa is considered vulnerable with only two small wild populations remaining. Both species have been planted widely outside their natural ranges, including in New Zealand, where they have naturalised.
Rare NZ species that have naturalised overseas
Are there any overseas ‘genetic reservoirs’ for our own native species? While there are no invasive populations of New Zealand birds or reptiles overseas there are now a large number of weedy New Zealand plants. However, most of these species are not threatened in New Zealand. I only know of one New Zealand ‘weed’ that is uncommon in its native distribution: New Zealand pygmyweed (Crassula helmsii). Although it is unclear whether this species is actually threatened in New Zealand, it has become a serious weed in Britain. Perhaps if it declines further here, we may need to repatriate it.