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establishing if they are accidentally or deliberately transferred to Antarctica. This is
abundantly clear in sub-Antarctic terrestrial ecosystems, which have had the longest
record of human in
uence and have the least extreme environmental conditions.
A range of vertebrates are present through both accidental (rodents) and deliberate
(farm animals, pets) introduction to most major islands. Although there have been
some control and eradication attempts, for example of cats from Marion and
Macquarie Islands and rabbits and rats from islands in the Kerguelen archipelago,
the consequences of these introductions may now be irreversible whilst, even if
possible in theory, the practicalities and costs of achieving effective control measures
for most species may be insurmountable. The impacts of some (particularly
predators and grazing mammals) are dramatic. There are also a wide diversity of
introduced plants on the sub-Antarctic islands, some of which may prove capable of
spreading further south as summer conditions warm.
In the marine environment, while there are currently very few con
rmed records
of introductions, our practical ability even to detect them is minimal, given the
limited spatial extent of survey data and equipment. In an analogous fashion on
land, and almost inevitably, introductions of less visibly obvious organisms
(invertebrates, lower plants, microbes) have received less or no attention. However,
it is clear that the vast majority of introductions overall have been accidental.
While the majority have existed only in concert with human occupation or activity,
some of those that have become established have gone on to become invasive, with
clear and harmful impacts on native ecosystems especially on the sub-Antarctic
islands. There is evidence of competitive displacement and local extinction of native
species, and in this context the introduction of new trophic levels to ecosystems
where they were previously unrepresented, such as predatory carabid beetles to
two sub-Antarctic islands, is particularly signi
cant.
Climate change and other human impacts
Antarctica has been a focus of biological studies aimed at understanding the
consequences of global climate change. Parts of the continent, in particular the
Antarctic Peninsula and Scotia Arc islands, have experienced the most rapid
temperature increases seen worldwide over the last 50 years or so. The polar regions
are also predicted to see the greatest and most rapid warming in future. Coupled
with this, the relative simplicity of their terrestrial ecosystems is seen as a tool with
which to identify more easily the ways in which ecosystems generally may be
vulnerable to or respond to processes of environmental change. While there is an
almost inevitable media focus on climate warming, climate change is a far more
complex process. For terrestrial biota, a second fundamentally important change lies
in precipitation patterns and form (snow vs. rain) as this alters water input to
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