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Wilkens, H., Culver, D.C. & Humphreys, W.F. (eds ) ( 2000 ) Subterranean ecosystems . Ecosystems of the World Book Series: Volume 30 , Elsevier Science, Amsterdam . xix + 791 pp , figs, tables, author, systematic and general indexes. Hardback: Price NLG 486.00 (Euro 220.54), US$254.50 . ISBN 0-444-82299-2 .

This splendidly edited volume introducing state-of-the-art biospeleology (the biology of caves, karst and groundwater), successfully captures both the challenge and the excitement of the discipline. It is a compilation of 36 articles contributed by 60 authors and covers a diverse array of topics, from faunistics to biogeographic regional analyses, from thorough descriptions of underground habitats and environmental conditions to experimental evolutionary research on so-called ‘troglobitization’ (the morphological, physiological and behavioural traits shared by most cave-adapted organisms, but whose adaptive condition still remains debatable). Aspects of trophic ecology in the subterranean environment are also presented, from descriptive contributions on odd resource types available in caves to innovative experimental analyses of food webs by means of stable isotope tracing. Biogeography is not neglected, including controversial general topics such as the colonization of, and speciation within, the subterranean environment, interspersed with phylogeographic case studies on selected taxa. All these issues are introduced as informative review chapters (frequently representing the synthesis of decades of work) combined with local case studies.

As the editors point out in the foreword, the hypogaean (underground) habitat is the most extensive terrestrial biome on Earth. The first section of the book establishes a firm setting for the subterranean scene. It begins with a thorough, no-stone-left-unturned contribution by Jubertie, in which virtually all hypogaean habitats developed in karstic terrains are categorized and described. Shallow interstitial aquatic habitats in unconsolidated sediments are the subject of the following chapter by Ward et al., although it is mostly devoted to hyporheic (groundwater beneath rivers) and parafluvial freshwater biotopes. One misses, however, a more thorough treatment of the marine interstitial, given its long-standing persistence in time, immense coverage, and extraordinary biological diversity. The transitional land–sea anchialine environment (coastal caves flooded with seawater) is treated by Iliffe, who emphasizes its unique hydrology and water chemistry; aquatic microbiologists interested in microstratified environments will find here a potentially interesting, neglected habitat. The picture is completed with the subterranean biotopes developed in volcanic landscapes, described succinctly in the above-mentioned chapter by Jubertie, but receiving a more thorough treatment later, in P. & M. Ashmole’s chapter 14 on hypogaean life in lava and tephra fields.

The subterranean bestiary fills another section of the book. Treatment of invertebrate groups is highly unbalanced, being limited to the most speciose taxon, the arthropods (chapters 4–5). Nevertheless, both contributions represent a very good introduction to the diversity of troglo- and stygobiont arthropod groups, permitting the non-specialist to browse further through the comprehensive species checklists available in the literature (e.g. Botosaneanu, 1986; Jubertie & Decu, 1994). I should point out here that the data given by H. Hobbs III on the world total of stygobiont crustaceans incorporates the over-estimation by Negrea (in Jubertie & Decu, 1994) concerning the number of truly stygobiont cladocerans. As far as I know, there are only four species described and not 24 (or 100) as stated; anomopod cladocerans are definitely a marginal group in the stygal. The synthesis by Weber (chapter 6) on cave fishes and salamanders is simply superb: all taxa known up to 1997 are listed, many are figured, and a plethora of information on natural history traits and biogeography is provided. This faunistic section is complemented with Iliffe’s chapter (chapter 3) on anchialine biology, where the world’s anchialine fauna is outlined.

The effects of darkness and of extreme oligotrophy on the cave fauna are surveyed in a separate section, with thorough reviews by Langecker and Hüppop, mainly based on cave vertebrates. Exciting new lines of research are highlighted: for example, that presumed adaptive characters of troglobitic vertebrates may only be by-products of endocrine adjustments; or that the direct absorption of calcium through the gills of cave fishes and neotenic salamanders (making them independent from vitamin D, the synthesis of which is mediated by UV radiation) could explain their relatively high diversity in caves compared with that of other vertebrates.

The role of regressive evolution in shaping the morphology of subterranean fauna, a central theme for research in biospeleology, is treated in several chapters, with a review of the classical hypotheses, whether they are based on direct or indirect selection (energy economy, pleiotropy), or on neutral mutation, but also suggesting novel approaches such as Coineau’s ingenious ideas on the role of heterochrony (evolutionary change related to changes in developmental timing). The reader will find a synthesis of the impressive cross-breeding experiments carried out by Hüppop and Wilkens with epigaean and troglomorphic populations of the Mexican characid fish Astyanax fasciatus. Although Hüppop modestly gives credit to other explanations not founded on experimental research (p. 175: ‘any discussion about which theory provides the main or universal explanation for regressive evolution is as useless as are the reduced characters in cave animals’), with the presently available genetic data it is hard to conceive a more tenable explanation for the acquisition of regressive features in cave animals than through the accumulation of neutral, structurally reducing mutations.

An overview of cave trophic ecology by Poulson & Lavoie (chapter 12) is complemented by several case studies showing some of the unusual resources exploited by cave communities, such as guano in tropical caves, aeolian ‘manna’ in barren lava and tephra fields, or submerged tree roots. Only the contributions by Pholman, Sarbu and co-workers on partially or totally chemoautotrophically based cave systems make use of the (expensive) stable isotope tracing techniques, and inject welcome rigour into the elucidation of cave food webs. The emerging picture suggests that the contribution of bacterial primary production in caves is quantitatively relevant only in some sulphide-based systems harbouring thermomineral waters (reminiscent of deep-sea hydrothermal vents), but not in those where it is achieved mainly through nitrification, as occurs in anchialine habitats.

The various derivations and modes of colonization and speciation of the cave fauna are the subject of a balanced overview by Holsinger (chapter 21), whereas the contributions by Sbordoni et al. and by Humphreys focus on the more orthodox explanations for its origin (i.e. the major role played by vicariance in the fragmentation of gene flow between epigaean and hypogaean populations, and in the succeeding speciation and troglobitization). The latter viewpoint is complemented by a case-study by Boutin & Coineau (chapter 23) which emphasizes the value of the thalassoid stygofauna as a palaeogeographic tool. Missing from this section of the book is some examination of the more ‘heterodox’ explanations for the evolution of troglobites. Thus, the so-called (parapatric) ‘adaptive-shift’ model of Howarth (originally proposed for lava tubes, and later extended to all caves types in tropical latitudes), or the sympatric model of Hüppop and Wilkens, are criticised on the basis of the absence of empirical data (i.e. of detailed genetic analyses) supporting the strict monophyly of the troglobitic populations and their alleged epigaean direct ancestors, which leaves open the alternative hypothesis that the sympatric occurrence of troglobitic species and their epigaean relatives in tropical caves is the product of secondary contact of populations already diverged in allopatry. This latter view is implicitly supported in Ashmole & Ashmole’s model for speciation in lava tubes triggered only by ecological succession (chapter 14).

The final sections of the book are devoted to regional ecological and faunistic studies, plus aspects of the conservation of the subterranean environment. From the zoogeographic point of view, two syntheses are remarkable: that produced by Humphreys on the Australian Cape Range cave fauna (chapter 3), with its spectacular array of lineages displaying extreme disjunct distributions; and that by Deharveng and Bedos on South-east Asian cave communities (chapter 31), a vast region still remaining virtually unexplored from the faunistic point of view. The latter chapter also introduces an interesting comparative approach to the cave community structure of tropical and temperate regions of the world.

The book is anything but cheap, but it should be on the library shelves of every academic institution.

Wilkens, H., Culver, D.C. & Humphreys, W.F. (eds ) ( 2000 ) Subterranean ecosystems . Ecosystems of the World Book Series: Volume 30 , Elsevier Science, Amsterdam . xix + 791 pp , figs, tables, author, systematic and general indexes. Hardback: Price NLG 486.00 (Euro 220.54), US$254.50 . ISBN 0-444-82299-2 .

References

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  2. References
  • Botosaneanu, L. (1986) Stygofauna Mundi: A Faunistic, Distributional, and Ecological Synthesis of the World Fauna inhabiting Subterranean Waters (including the Marine Interstitial). E.J. Brill, Leiden.
  • Jubertie, C. & Decu, C. (1994) Encyclopaedia Biospeologica, Vol. I. Société de Biospéologie, Moulis (France) and Bucarest.