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Book Review: The Biology of Varanid Lizards (2nd edition) Print E-mail
Book Review from mampam.com

© Daniel Bennett 2001

Monitors. The Biology of Varanid Lizards (2nd edition). Dennis King and Brian Green

(1999). 134 pp. Krieger Publishing Company, Malabar, Florida. US$25.50 (paper)

Rating (out of ten) = 5

Monitor is the second edition of a book originally published in 1993 as "Goanna. The Biology of Varanid Lizards". I suspect the new title is intended to give the book a wider appeal outside Australia. The book deals largely with the biology of Rosenberg's monitor lizard Varanus rosenbergi, and compares its biology to that of other Varanus species. It is extremely well written, at a level that biology students will have no problems with. Twenty one colour pates are included, six of them new additions.

The introductory chapter, like most of those following, is largely unchanged from the first edition. It includes a brief discussion of the evolutionary history of the monitor lizards, the largest and smallest monitors and the family's distribution. The taxonomy and phylogeny chapter discusses the fossil history of the group and changes in extant varanid classification since the work of Robert Mertens. It ends with a statement that the recognised subgenera are probably different enough to warrant generic status, which should keep the next generation of taxonomists in business for some time.

The chapter on feeding covers the diets of various monitor lizards, the use of olfaction for finding food and the morphology and function of the tongue, hyoid apparatus, jaws and teeth. A few inaccuracies and unjustified generalisations are apparent in this chapter. V. olivaceus occurs only in the northeast of the Philippines, not on the southern islands and it is frugivorous rather than herbivorous. The teeth of varanids are not "always sharp and recurved". Several species undergo an ontogenetic change in tooth shape that results in broad, crushing teeth for dealing with hard shelled prey. According to the text both V. salvator and V. griseus regularly eat snails. Neither species possesses crushing dentition and this claim is unsubstantiated in the literature, as far as I am aware. It seems particularly unlikely in the case of V. griseus, which inhabits desert regions where snails are very rare.

Chapter 4 covers reproduction. The authors note that only one species of monitor (V. salvator) is known to produce more than one clutch of eggs per year. They concede that other species do so in captivity, but attribute this to "an unnaturally abundant supply of food". In fact multiple clutching in wild monitors is probably overlooked because virtually everything we know about their reproductive biology comes from investigations of the insides of dead animals. The frequency and speed at which monitor lizards can produce clutches of eggs in captivity, and their largely unfussy diets, makes it almost inconceivable that multiple clutching is either a rare phenomena in the wild or that it only occurs in a few species. The most exciting studies of breeding behaviour in recent years, by Tsellarius and Tsellarius (1996, 1997) on V. griseus, are mentioned in the text, but no references are given. Similarly, in Chapter 5 (General Behaviour) much is made of the ability of V. albigularis to count snails, but the work (Kaufman et al. 1996) is not listed in the references. Chapters 6-9 cover thermal biology, respiration, water use and energy and food. They are the most valuable parts of the book, providing concise details of aspects of Varanus physiology not available elsewhere. The authors emphasize the fact that monitor lizards can survive with very little energy input, but do not mention the lizards' extraordinary ability to assimilate large amounts of energy when it is available. The data presented for V. rosenbergi are interesting and convincing, but some of the more general tables are querulous. Table 6.2 lists activity temperatures taken by telemetry from various studies around the world, but the figures are scarcely comparable given the differences in methodologies used. Table 6.3 is devoted to one-off cloacal temperature readings for a variety of species in the wild and in captivity and is not at all enlightening. The penultimate chapter covers parasites and is new to the second edition. The life cycles of hard ticks are discussed and a variety of endoparasites known to infest monitor lizards are listed. The final chapter, Conservation and Management, is the one that I had most problems with. I would have liked to have seen the authors take a less opinionated stance. The authors discuss conservation by region and state that whilst all species in Australia are safe as a result of enlightened legislation, those in Asia and Africa are threatened by exploitation, primarily for the leather trade. In fact exploitation of monitor lizards in most places is exclusively for meat. They omit to mention that the countries that export lizard skins are unusually poor (e.g. Sudan, Chad and Mali) and whilst admitting that there is little (if any) evidence that exploitation has had a detrimental effect on populations, they consider it "likely" and state that reducing demand for skins would reduce the overall threat to the animals. In my opinion habitat destruction (primarily the removal of forests and mangroves) is by far the greatest threat facing monitor lizards in Africa and Asia. The authors relegate this factor to a small paragraph at the end of the chapter.

In summary, this book is a very useful guide for anyone with an interest in the biology of monitor lizards and a thorough treatment of the biology of V. rosenbergi. The authors are the best qualified guides to the subject you could hope for and the chapters on physiology are outstanding. But if you already own the first edition you should save your money. The amount of new material in the second edition is disappointing and many of the more interesting statements are not supported by references. The biggest weakness of this book is the lack of direct referencing and the very inadequate bibliography. Readers wishing to learn more about a particular subject are directed to a condensed list at the end of the book arranged by chapters, which will limit the usefulness of the book to students and researchers to some extent.

Kaufman, J.D., Burghardt, G. M. and J. A. Phillips. 1996. Sensory clues and foraging decisions in a large carnivorous lizard, Varanus albigularis. Anim. Behav. 52:727-736.

Tsellarius, A. Y. and E.Y. Tsellarius. 1996. Courtship and mating in Varanus griseus of Western Kyzylkum. Russian Journal of Herpetology 3(2): 122-129.

Tsellarius,A.Y. and E.Y. Tsellarius. 1997. Behavior of Varanus griseus during encounters with conspecifics. Asiatic Herpetological Research 7:108-130.
 
 

 

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