PrefaceAustralia is a dry continent with well over 70% of its land area generally classed as arid or semi-arid, and for 200 years it has been known to possess a distinctive flora and fauna, as documented in the recently published Ecological Biogeography of Australia. The topic of the evolution of the biota of and Australia raises a variety of questions. What are the origins and history of the flora and fauna? Are there substantial endemic elements or do affinities lie in other parts of Australia or beyond? What has been the history of aridity? What adaptations, life histories, breeding systems and evolutionary strategies have been selected? What are the predominant patterns of diversity, within arid Australia and in relation to other, less and parts of the continent? In the flowering plants for instance, only about 2000 species, or one tenth of the Australian total of some 20,000 species, are recorded in the recent Flora of Central Australia which deals with an area equivalent to a quarter of the continent. This compares with more than 2000 species listed in the Flora of Sydney Region encompassing only about 20,00O square km. In contrast, among the insects, the ants of dry inland Australia are remarkably diverse, apparently far more so than those of comparable and regions in other continents. This volume is the result of a Symposium held in Adelaide in 1980 to consider some of these and other questions relating to the Evolution of the Flora and Fauna of Arid Australia. The time and place were appropriate. The Australian Systematic Botany Society was in the process of compiling the Flora of Central Australia, and Adelaide, the closest of the State capitals to the and zone, has been the centre for much research into arid-zone biology. The Symposium was based on a series of review papers around which other contributions were organized. It was our intention to cover a variety of topics ranging from the nature and history of Australia's arid environments to the historical biogeography of their biota and the evolution of adaptation to aridity. Actual coverage was limited by two factors. First we tried to avoid, so far as possible, overlap with two symposia on allied topics that have been held in recent years. One, at the Australian Museum, Sydney, covered arid Australia in general and not in a specifically evolutionary context; the other at Canberra, dealt with Biology and Quaternary Environments. The second constraint was the availability of expertise on different groups of organisms and variation from group to group in the extent of basic biogeographical and taxonomic knowledge. At one extreme, Australian research on vertebrate animals has reached a relatively advanced stage. The nomenclature is more or less stable and a considerable amount of information is available on ecology, genetics and patterns of distribution. Here we could look for contributions on each main group, and background knowledge is sufficient to permit either broad reviews of biogeographical history or detailed consideration of ecological, physiological and other adaptations to aridity. Research on higher plants is at a somewhat earlier stage. There have been studies of ecophysiological and breeding systems and, recently, the rate of production of revisions of genera that occur in the arid zone has increased. Herbarium collections of other genera are such that they are available for revision. These revisionary studies provide material for evolutionary and biogeographical analysis. At the other extreme, our knowledge of the terrestrial invertebrates of the and zone, their representation in collections and their coverage in this volume are very poor. This is despite their overwhelming contribution to the total biological diversity of and Australia and reflects the taxonomic difficulties that they present. Considering their significance to critical processes such as pollination, this represents a major gap. Nevertheless there are contributions here on three of the functionally most important hexapod groups and a representative group of arachnids. In order to allow maximum flexibility we did not attempt to define 'arid' or 'arid zone' or to delimit the area of the continent to be covered. This allowed inclusion of comparative data from adjoining less and areas and it proves to have been a fortuitous decision. One point to emerge from the Symposium was the importance, to the arid zone, of evolutionary events in these surrounding areas with more seasonal and predictable climates. This does mean that the reader should beware of differences between authors in their interpretation of 'arid'. In particular, the term 'central Australia' is used in two ways: precisely, to refer to defined regions within a wider and zone and, more loosely, to describe the central, inland part of the continent. A number of new facts and novel points are presented in the papers collected here and we hope that they may form an introduction and perhaps impetus for further studies. We should make it clear though that they are by no means a comprehensive treatment of evolution in arid Australia and there are many points that are not touched upon. To take but one example, it became clear at the Symposium that the origins of some of today's arid-zone biota may have to be sought far back in time. However, no contributor to this volume mentions K.H.L. Key's proposition, put forward for morabine grasshoppers, which relates modern distributions and centres of diversity to what are now regions of high relief but, at the same time, are also areas that persisted as dry land throughout the Cretaceous and early Tertiary period of epicontinental seas. Consequently the possibility must be entertained that certain distribution patterns, apparently centred on high relief refuge areas, may be relicts of the distribution of early Tertiary or even older land-masses. The question of the antiquity of some elements of the biota leads to another point. We feel it is necessary to warn against the extension of any schism between 'centre of origin, dispersal' and 'vicariance' approaches to biogeographical and evolutionary studies in Australia. The potential for such a division can be seen in this volume. There are groups that have penetrated the and zone following relatively recent arrival in Australia. A centre of origin, dispersal approach may be applied here and colonization, adaptation and divergence can be treated as continuing processes. At the other extreme, some groups do seem to be ancient and have left few clues to the sequences of dispersal and speciation that constitute their biogeographical and evolutionary history. Here a vicariance approach allows their investigation in terms of present distributions and what we know of the geography of Tertiary or earlier terms. The two approaches need not be mutually exclusive, especially if certain environments favour evolutionary strategies that lead to stable, conservative genetic systems so that taxa can survive for long periods with little change so long as the environment persists. The original 1980 symposium owed much to the efforts of our fellow members of the informal organizing committee, Dr judy West, Dr P.R. Baverstock and Dr W.R. Breed. For assistance in a variety of ways we are grateful to the Australian Systematic Botany Society, the South Australian Division of ANZAAS, Mrs R.M. Barker, Dr B.A. Barlow, Dr R.C. Carolin, Dr J.P. Jessop, Dr W.A. Low, Mr E. Slater, Dr O.B. Williams, Dr J.T. Wiskich and Mr E.N.S. Jackson and other colleagues at the Adelaide Botanic Garden and at the Division of Soils, CSIRO. Dr R.J. Wasson did not present a paper at the Symposium but subsequently he very kindly provided an account of landform development to fill a gap in the topics covered. We must single out one individual for special mention, Professor S. Smith-White, for his interest in the Symposium and for his concluding review. We are aware of the high price in Australia of some books similar to this and of the need for economical publications within the financial reach of the individual. We thank Mr John Scardigno of Peacock Publications for acknowledging this need.
W.R. Barker
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