Influences on and Origins of Terrestrial Biodiversity of the Sub-antarctic Islands

. Ihe "sub-Antarctic" is a region of the planet characterised by small and extremely isolated island landmasses set in the vastness and harsh conditions of the Southern Ocean. Although there is no universally applicable definition of the sub-Antarctic, based on eeo-climatic criteria (temperature and the presence/absence of trees or woody shrubs) a useful terrestrial biogeographic region can be defined that includes only those islands which lie close to the oceanic Antarctic Polar Frontal Zone (PFZ). These range between roughly 4rS and 54°S and include South Georgia in the South Atlantic sector of the Southern Ocean, Marion and Prince Edward islands, lies Kerguelen and Crozet, and Heard and McDonald islands in the Indian Ocean sector, and Macquarie Island in the Pacific Ocean sector. These islands have widely differing origins and geological histories. This paper provides an overview of their biodiversity and of the major patterns in biogeography. The majority of islands are of relatively recent origin, and there are only very limited indications of a more ancient biogeographical history (Gondwana-breakup timescale) to be found in the contemporary biota. Amongst the sub-Antarctic biota, there are examples supporting two general hypotheses relating to their origin: the Insulantarctic and the multi regional scenarios. Sub-Antarctic terrestrial ecosystems, which are of biodiversity and conservation significance globally, are under considerable eontemporary pressure through the twin influences of possible anthropogenic climate change, and the introduction and establishment of invasive non-indigenous species.