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In this paper we consider the extent of our knowledge of global beetle diversity. Depending on the estimates adopted, some 70–95% of all beetle species remain to be formally described, and at the current rate of progress it could be more than 200 years until the task is completed. One of the reasons for this is the difficulty of adequately sampling tropical beetle faunas and thereby ensuring sufficient material is available to taxonomists for comparative studies. Despite this, recent years have seen significant advances in our understanding of beetle taxonomy, biology, ecology and biogeography, and we are now in a good position to apply this understanding to ecological and management issues. Saproxylic (dead-wood-associated) beetles are used to illustrate this latter point. © CSIRO 2000 Introduction ‘What is the diameter of the Earth? It is 12 742 kilometres. How many stars are there in the Milky Way, an ordinary spiral galaxy? Approximately 1011, 100 billion. How many genes are there in a small virus? There are 10 (in fX174 phage). What is the mass of an electron? It is 9.1 × 10–28 grams. And how many species are there on Earth? We don’t know, not even to the nearest order of magnitude. The number could be close to 10 million, or as high as 100 million.’ – Wilson (1992). ‘J.B.S. Haldane was once approached by a distinguished theologian to ask what inferences one could draw about the nature of the Creator from the study of His creation. He replied with his usual terseness, ‘An inordinate fondness for beetles’.’ – Evans (1975). The above quotations make it clear that although we know surprisingly little about the extent of life on Earth, we do know that insects, and in particular beetles, are by far the most species-rich life form on Earth. And yet insect and beetle diversity is so vast that it is easy to lose sight of the extent of our current knowledge. In this paper, we seek to address four questions. (1) How diverse are beetles compared to other life forms? (2) How far have we gone towards describing the world’s beetles? (3) How much do we know about these species? (4) How can we apply our knowledge of beetle taxonomy and biology to ‘real world’ issues? In doing this, we pay tribute to the critical contribution that John Lawrence has made to understanding the fundamental relationships of beetle groups, particularly to the less charismatic and yet systematically and ecologically highly significant groups. His contribution to beetle systematics, and to the public understanding of this subject, is internationally recognised, and his work on beetle taxonomy and biology has made it possible for others to consider including in their own studies some of the less well-known beetle groups, where much of the extraordinary diversity resides. How diverse are beetles compared to other life forms? Many attempts have been made to estimate the total number of described species of organisms (Stork 1988, 1993, 1997, 1999a, 1999b; Hammond 1992, 1995, 1996; May 1999). Currently the total stands at between 1.5 and 2.2 million species. The uncertainty about this number is because there is no comprehensive catalogue of all described species. As all taxonomists know, this situation is exacerbated by the fact that many species are often described more than once, while some described species are in reality a complex of many species. Thus, while many thousands of new species are described every year, many of these will turn out to be synonyms while others will ultimately be recognised as comprising several species. Taking synonyms and species complexes into account, May (1999) calculated that the number of actual species described would only equate to about 75% of current estimates. The largest proportion of described species are insects, and of these, the greatest proportion are beetles (Fig. 1). We are uncertain of the true total number of described beetle species, but it is likely to be around 300 000–450 000 species (e.g. Nielsen and Mound 1999), or in other words, up to a fifth of all described species. This is more than twice the number of described species in any other insect order. S.J. Grove and N.E. Stork 734 Why is it that so many species of beetles have been described, and has this group received greater attention than other groups of insects? The answer to the first question is complex. It would appear from a number of studies that beetles are indeed as species-rich as the number of described species would suggest. For instance, beetles comprise about 20% of the well-known British insect fauna, and a few key studies of tropical faunas (e.g. Hammond 1990; Stork 1991) indicate that beetles may comprise an even larger proportion in the tropics. Beetles would appear to be the most ecologically diverse of all groups of insects, occupying almost all terrestrial and freshwater habitats and ecosystems. Beetle families dominate the list of the most species-rich families of insects. As to the second question, it would seem unlikely that beetles have received more attention from taxonomists than other groups, and certainly less attention than the more charismatic groups such as Lepidoptera and Orthoptera. It would appear that beetles really are as species-rich as the figures suggest. How far have we gone towards describing the world’s beetles? Hammond (1992) showed that description rates for new species have been surprisingly consistent over the last decade or so. Each year a total of about 2000–2500 beetle species are described as new, whereas about 500 species are recognised as synonyms and are sunk: a net increase per year of about 2000. It is worth considering how long it will take taxonomists to describe all the world’s beetles at this rate, but to do so we need to have an estimate of how many undescribed species there still are. In Erwin’s famous calculation of 30 million species as an answer to how many species of insects there are on Earth (Erwin 1982), he estimated that 12 million of these species were beetles. He had collected over 1200 species of beetles from a single species of tree in Panama by canopy fogging and had suggested that of these 162 species (13.5%) were specific to that tree, that 50 000 tree species in the world might also each have this number of host-specific beetle species, and that the canopy is twice as rich in beetle species as the ground. Erwin’s estimates have not gone unchallenged. One of the main areas of uncertainty in his calculations is the level of host specificity. Erwin assumed an average level of 13.5% specificity of canopy beetles to a particular tree species but had no evidence for this. May (1990) attempted to find a mathematical solution to this problem. Using data on British beetles and trees, his model predicted that 10% of the beetles were herbivores specific to the tree genus Quercus. However, most studies would indicate that Erwin’s and May’s figures Fig. 1. Described (shaded) and estimated (clear) numbers of species for different taxonomic groups, based on an estimated global total of 14.9 million species (from Stork 1999a, after Hammond 1992).