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Some of today's most pressing issues deal with invasions by alien species into natural or man-made ecosystems such as agricultural landscapes. Invasions are not a new phenomenon having been a part of the relationship between man and the environment ever since humans moved out into the savannas; however, they became part of the ecological agenda in the middle of the last century. The foundations of invasion ecology stem from Charles Elton, who, in his book, The Ecology of Invasions by Animals and Plants (published in 1958) attempted to draw together three stands of ecology – faunal history, ecology, particularly population ecology, and conservation. Elton's book had some traction at the time (e.g. Baker and Stebbins 1965), however, few ecologists paid much attention to invasions during the 1960s even though island biogeography theory (MacArthur and Wilson 1967) did provide theoretical frameworks for how new species fitted into the resident species communities on islands. It was not until the 1970s that invasion ecology began to gain traction in the literature (e.g. Baker 1974; Embree 1979) and continues to this day (Richardson 2011). There have been recent attempts to create unified theoretical frameworks for understanding the invasion process (Blackburn et al. 2011) and the traits that determine the degree to which a species can invade a new ecosystem or the degree to which an ecosystem can be invaded by a new species (Richardson and Pysek 2006). These developments provide a foundation upon which to assess the degree to which hypotheses concerning biological invasions relate to real-world case studies that are proliferating in the literature.

Many conservationists argue that invasive species form one of the most important threats to ecosystems the world over, often spreading quickly through their new environments and jeopardising the conservation of native species. As such, it is important that reliable predictions can be made regarding the effects of new species on particular habitats. This book provides a critical appraisal of ecosystem theory using case studies of biological invasions in Australasia. Each chapter is built around a set of 11 central hypotheses from community ecology, which were mainly developed in North American or European contexts. The authors examine the hypotheses in the light of evidence from their particular species, testing their power in explaining the success or failure of invasion and accepting or rejecting each hypothesis as appropriate. The conclusions have far-reaching consequences for the utility of community ecology, suggesting a rejection of its predictive powers and a positive reappraisal of natural history.

Just as the proof of the pudding is in the eating, so it is in science that the testing of hypotheses is at the core of the development of theory. As set out in this book's Introduction (Chapter 1), most ecological theory has been developed outside Australasia; this biogeographical region thus provides an excellent case study for investigating whether the generally accepted hypotheses from ecological theory really are applicable in a different context. Furthermore, many excellent observational studies have been carried out in Australasia; the history of invasions in that region can be viewed as a series of experimental tests of ecological theory. Indeed, the Australian native flora and fauna was so different from that of the rest of the world, that Darwin (before he became an atheist) asked himself in his diaries whether there had been two Creators instead of one (see Chapter 1). In Chapter 1, we explained the reasoning behind the selection of the hypotheses that are reviewed in the main chapters in this book. At the beginning of this project all the authors were asked to formulate hypotheses, to give their feedback on the hypotheses, the way they were formulated and whether the hypotheses could be assessed by them; as a result of this collective effort authors could agree on assessing this present set of hypotheses. The hypotheses are derived from general ecological theory (see Chapter 1) but the material at hand cannot be viewed simply as 'data' such that the hypotheses can be tested as a part of statistical inference. This type of inference is familiar and easy for most scientists to address, and that is where most authors of this book clearly felt more secure than when they had to arrive at judgements from observations or from historical reconstructions. The overall conclusions, based on a meta-analysis of the assessment/testing of the 11 hypotheses by the authors of the chapters on species that moved into or out of Australasia as presented in the following tables, are clear: after weighing up the evidence many of the authors of chapters in this book concluded that there was no support for the individual hypothesis, or that they had to reject the hypothesis.