Answer: New Zealand

Prior to human colonization, the island of New Zealand was curiously devoid of nearly all mammal species. Before humans arrived there were just three species of bats, seven species of seals and sea lions, and a few dozen species of whales and dolphins that dotted the coastal regions. By comparison, places like North America and Europe have enormously diverse species of mammals ranging in size from tiny mice and voles all the way up to large and lumbering herd animals.

New Zealand stayed in such a state until the arrival of the Māori around the middle of the 13th century (along with themselves and their gear they also brought dogs and rats from the Polynesian islands). Later, with the arrival of Europeans in the 18th century, pigs, mice, more rats, weasels, stoats, ferrets, possums, and more mammals arrived on the island. By the middle of the 19th century there were also Fallow deer and somewhere around 1900 even moose were introduced.

While human colonization certainly expanded the roster of mammals, it wasn’t without problems: animals like rats and cats pose a threat to local species both through their over consumption of resources and the aggressive way in which they have consumed the eggs and young of indigenous animals (a problem which, not unsurprisingly, also plagues other islands like Hawaii and Madagascar).