Invasive/ Introduced Species.
New Zealand is extremely aware of their invasive species, and they love telling everybody about them (plus I did a paper on "The Impact of Introduced Species on New Zealand Biodiversity"). That picture at the top? That is a common brushtail possum, native to Australia. They were introduced to NZ in the late 1800s in the hope to start a fur trade. Those cute, fuzzy, and ridiculously soft creatures are really rampaging killers. No, seriously. Possums love to eat birds. And, if you didn't know, almost all of NZ's native species are birds. These birds evolved without any major predators
to worry about, thus not evolving an instinctive anti-predator behavior. So combine these helpless birds with more than one new predator (the stoat is another major problem species), and without interference the birds will be gone sooner rather than later.
Luckily NZ is aware of these issues and participates in measures to prevent the extinction of all of their native flora and fauna. While the United States may not have any species that is quite this bad, at least not nationally known (cane toads are a big problem in Hawaii), we do still have a lot of invasive species and such. I mean, just think of the size of this country. We're bound to have a few problems.
If your interest has been piqued by this post, you can find a list of invasive species in the United States (by state) here. Or you can just try Wikipedia. Despite the reputation, most of Wikipedia's articles are mostly correct. After a quick scan of this article I believe you can gain some useful, true information.
And on that note I am off to bed. It's been a long day and my pillow is just calling my name. Tomorrow's letter is J... I wonder what I'll come up with for that?