Geoscience Reference
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intriguing possibility of containing microbial communities that have evolved in
isolation for hundreds of thousands of years.
Biological history and colonisation processes
The Antarctic terrestrial biota has obvious linkages with the other southern
continents, particularly evident in the
flora. This, along with the perceived wiping
out of terrestrial habitats as ice sheets expanded at glacial maxima, has led to a view
that today
is biota is largely a result of recent colonisation as post-Pleistocene
deglaciation progressed. Despite the continent
'
s geographical isolation and extreme
conditions, colonisation processes plainly continue to operate, albeit at very low
frequency. Some Antarctic biological groups appear to possess features that are
supremely well adapted to facilitate long-distance dispersal, for instance, the spores
and vegetative propagules of mosses and lichens, the resting tuns of tardigrades and
the many well-expressed ecophysiological adaptations to cold and desiccation
stresses. There are well-documented instances of plant and microbial groups found
in Antarctica (both widespread and as single records) with wider bipolar or
temperate/tropical montane distributions.
Amongst many of the groups of biota that dominate Antarctic terrestrial
ecosystems (mites, springtails, tardigrades, nematodes, lichens, but not mosses)
there are many examples of high levels of endemism, both to the Antarctic in
general, and to speci
'
c subregions within Antarctica. These are now used to support
a hypothesis of prolonged regional presence (
) rather than recent
colonisation. Molecular biological techniques have given a new approach to
estimating divergence dates between related organisms. These have demonstrated
radiation processes over millions of years in the springtails of the Transantarctic
Mountains and Victoria Land, and even older separation events in the Antarctic
Peninsula and Scotia Arc, with divergence of closely related species of endemic
'
vicariance
'
ies
possibly coincident with the tectonic separation of the Antarctic Peninsula from
South America on timescales of 30
40million years or more.
While the strength of evidence supporting the generality of vicariance as
underlying a large proportion of the present day terrestrial biota of Antarctica is
rapidly increasing, there has been less progress in identifying speci
-
c refugial
locations. Indeed, this may never be possible, as it is a feature of repeated glacial
and ice sheet advance and retreat cycles that the small-scale detail of ice boundaries
is very variable, while successive advances obliterate evidence of previous
boundaries. It is undoubtedly the case that, at glacial maxima, far less exposed
terrestrial ground was available than is the case even now. This inevitably means
that, with each cycle of glacial retreat comes the opportunity for
'
'
local
-
recolonisation from refugia
this, for instance, must underlie the contemporary
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