Australia: The Land Where Time Began

A biography of the Australian continent 

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.

Sources & Further reading

1. Heads, Michael, 2014, Biogeography of Australasia: A Molecular Analysis, Cambridge University Press