Geoscience Reference
In-Depth Information
present. Mites and springtails can be abundant, with high densities comparable
with many temperate ecosystems, and micro-invertebrates are also numerically
abundant. In all these groups, species diversity is low. Food webs are
characteristically simple, with most energy
flow through the decomposition cycle
and negligible impacts of predation or true herbivory. The continental Antarctic
provides an even simpler fauna, with no insects, and much more limited presence of
micro-arthropods. The simplest faunal ecosystems yet known on the planet are
found here, where even nematodes are absent.
The Antarctic
flora is generally well described, and shares several features with
the fauna. The sub-Antarctic is again richest, and shows relationships with the
oras
of the relevant nearest continents or landmasses. The strictly de
ned sub-Antarctic
is characterised by the absence of trees and shrubs. Although often described as
comparable with Arctic tundra, the sub-Antarctic differs in important features, in
particular in not being in
uenced by permafrost and in the absence of woody plants.
A particular feature of sub-Antarctic vegetation is the presence of large
'
megaherbs
'
and tall grasses, whose evolution is thought to have been encouraged by the
complete lack of vertebrate grazers.
Vegetation communities of the maritime Antarctic, along with higher altitude
areas of the sub-Antarctic and much more limited coastal areas of East Antarctica,
host cryptogamic communities of carpet- and turf-forming mosses. Extensive areas
of vegetation are only found over a narrow altitudinal range and near the coast.
Only two
flowering plants are present on the Antarctic continent, both limited to
the Antarctic Peninsula, and both also found in the Andes and Tierra del Fuego of
South America
these are the Antarctic hairgrass,
Deschampsia antarctica
, and
Antarctic pearlwort,
Colobanthus quitensis
. As conditions become more extreme,
particularly moving into the continental Antarctic, closed moss turves are replaced
by open fell
-
eld moss and lichen communities, and mosses gradually decrease in
abundance and diversity.
While there is implicit recognition within the descriptions above that microbial
groups must make an important contribution within Antarctic terrestrial
ecosystems, along with a more general recognition that microbial activity is
fundamental to ecosystem processes, the microbial elements of Antarctic ecosystems
have received surprisingly limited attention to date. Microbes are central to the
primary colonisation and stabilisation of mineral soils, subsequently permitting
colonisation and succession by other biota. Microbes also are the only living
components of some of the most physically extreme ecosystems on Earth that
are found in Antarctica. These include habitats described as cryophilic (between
ice crystals), chasmoendolithic (within tiny cracks that are open to the rock
surface) and cryptoendolithic (within microscopic cavities of the rock matrix).
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