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Australia: The Land Where Time Began |
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Biogeography of Australia – Distribution within Australia
Phylogenetic links – coasts and central deserts There is a distinctive biota in the arid central
part of Australia, also referred to as the Ermean or Eyrean region, and
the explanation of its history has been one of the most difficult
problems in the biogeography of Australia. Affinities have often been
described between the biota of the desert and the coastal biota, and
writing about many elements from central Australia it has been said that
they may have developed from species that are associated with habitats
on the coast (Burbidge, 1960: 106). Many calcicoles (plants adapted to
lime-rich soils) and halophytes as well as xerophytes are included among
the flora of central Australia, all of which can be derived from
shoreline floras. In central Australia there are many
salt lakes,
especially in the south-central and southwestern areas, the salt being
derived either from erosion of marine strata or from sea salt that is
airborne. The halophytes around the saline lakes, that have been a
feature of the flat landscape for a very long time, have very high
levels of diversity (Hopper, 2009). In this location typical halophyte
families, e.g., Chenopodiaceae, have a degree of endemism, and also
among the dominant trees, such as individual series and species of
eucalypts, and ancient links with the coast are preserved among these
communities that inhabit the area around the margins of salt lakes. The
sources of most of the large rivers in the southwestern parts of
Australia are in salt lakes, and some level of salinity is tolerated by
the riverine plants (George, 2009). Among these riverine trees are
paperbarks,
Melaleuca: Myrtaceae,
flooded gums,
Eucalyptus rudis:
Myrtaceae, and sheoaks,
Casuarina: Casuarinaceae.
There is also a diverse fauna that is associated with the salt lakes,
e.g., there are more autochthonous shore and water birds in the
Australian arid zone than anywhere else in Australia, in spite of its
lack of permanent rivers and lakes (Schodde, 1982). The salt lakes are
visited by most Australian waterfowl where they feed on the abundant
populations of invertebrates. It is suggested by the distribution and
phylogeny, as also occurs with plants, that this ecology dates from the
Mesozoic, the ancestral groups being associated with the inland seas
from that distant time. Dispersal inland, which occurred long after the
retreat of the inland seas, has been used most often to explain the
close affinities between the floras of the desert and those of the
coast. It has been suggested (Crisp et
al., 2004) that pathways
between these habitats may be revealed by molecular studies, possibly
along riverine flood plains. Heads1 suggests the dispersal of
coastal, weedy groups far inland along valleys and flood plains probably
occurred as the entire communities expanded at the time of the flooding
during the Cretaceous rather than the
Cainozoic. He also suggests that
differentiation resulted from phases of flooding and regression of the
inland seas.
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Author: M.H.Monroe Email: admin@austhrutime.com Sources & Further reading |