Exotic vertebrate fauna in the remote and pristine sub-antarctic Cape Horn Archipelago, Chile

Pristine wilderness is a scarce global resource, but exotic species are so common that they constitute a principal component of worldwide ecological change. The relationship between these two topics, invasion and remoteness, was the impetus behind five years of fieldwork aimed at identifying the assemblage and range of exotic vertebrates in Cape Horn, Chile, identified as one of the world's most pristine wilderness areas. While the archipelago has extremely low human population density and vast tracts of undisturbed land, we discovered that several terrestrial vertebrate groups were dominated by exotic species. Native birds were diverse (approx. 154 spp), and only 1.3% (or two spp.) were introduced. In contrast, exotic terrestrial mammals (12 spp.) and freshwater fish (three spp.) outnumbered their native counterparts, constituting 55% and 75% of the assemblages. Using GIS, we found that not all areas were impacted equally, largely due to intensity of human occupation. Human settled islands (Navarino and Tierra del Fuego) hosted the greatest number of exotics, but humans alone did not explain observed patterns. Remote islands also had introduced species. North American beavers (Castor canadensis), American minks (Mustela vison) and feral domestic dogs and cats were particularly widespread, and their range in isolated parts of the study area raised important ecological and management questions. In conclusion, the Cape Horn Archipelago retained areas free of exotic vertebrates, particularly parts of the Cape Horn and Alberto D'Agostini National Parks, but at many sites introduced species were overwhelming native biota and altering these previously remote natural ecosystems.