Surveying Biodiversity of Soil Herpetofauna: Towards A· Standard Quantitative Methodology
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Available online at www.sciencedirect.com -" EUROl'fAH JOURAAL OF -;;- ScienceDirect SOll BIOLOGY ELSEVIER European Journal of Soil Biology 42 (2006) SI03-S110 http://france.elsevier.comldirectlejsobi Original article Surveying biodiversity of soil herpetofauna: towards a· standard quantitative methodology G.J. Measey* Laboratoire d'Ecologie des Sols Tropicaux (UMR 137), Institut de Recherche pour le Développement (IRD), 32, avenue Henri-Varagnat, 93143 Bondy cedex, France Available online 07 August 2006 Abstract Soil herpetofauna biodiversity is conservatively estimated as 2775 species, made up of 10% and 28% of Amphibia and Squa mata, respectively. Neglect in their taxonomy, ecology and standard samp\ing methodologies suggests that proportions, as weIl as numbers, are \ikely to be far higher. Like invertebrate soil macrofauna, the majority ofspecies \ive within the first few centimetres of leaf \itter and soil. Results of 30 quantitative and 52 semi-quantitative surveys in nine regions of three continents show that these are infrequently encountered, whereas dedicated subterranean burrowers can be found at high densities, up to 0.844 indivi duals m-2 (x = 0.26). This suggests that a two tier sampling approach may be most appropriate, with superficial excavations in a 2 large quadrat (e.g. 25 m ) in addition to a smaller deeper subsample. It is hoped that this contribution will stimulate further discussion towards a consensus, filling the gap for a standard method ofquantitative surveying of soil herpetofauna biodiversity. © 2006 Elsevier Masson SAS. AlI rights reserved. Keywords: Standardised sUlVeys; Scolecophidian snakes; Gymnophiona; Amphisbaenians 1. Introduction fauna, re1ying on natura1 historians and the simp1y cur ious depositing specimens in museum collections [5]. It is wide1y recognised that soi1 flom and fauna have A1though these va1uab1e specimens have served as a 1agged behind their terrestria1 counterparts in terms of usefu1 starting point, many species are on1y known eco10gica1 studies [1]. Furthermore, the re1ative1y few from the very few individua1s that were originally co1 taxonomie studies on soi! organisms have resu1ted in an 1ected [6], and sometimes important detai1s are missing under appreciation of their importance to biodiversity from information associated with these specimens [7]. [2]. Soi1 herpetofauna, reptiles and amphibians, are no Even when collections have been extensive1y documen exception. For examp1e, Biju and Bossuyt [3] recentIy ted, resu1ting data can be of 1imited comparative use described a new fami1y of anurans from a single speci un1ess standard samp1ing methodo10gies have been fo1 men of a fossoria1 species, a feat considered to be simi 10wed. At present, for soi! herpetofauna, no wide1y lar to the first discovery of a living coe1acanth [4]. accepted standard samp1ing methods exist [8,9]. Historically, the discovery and description of soi! Do we need standard techniques to survey the bio herpetofauna has been 1ike that of all other flora and diversity ofsoi! herpetofauna? Biodiversity assessments require proven techniques [8], and it is becoming c1ear • Tel.: +33 1 48 02 59 62; fax: +33 1 48 02 59 70. that these are not capable of finding apparentIy com E-mail address:[email protected] (G.I. Measey). mon fossoria1 herpetofauna1 taxa [lO,ll]. C1ear1y for 1164-5563/$ - see front matter © 2006 Elsevier Masson SAS. Ail rights reselVed. doi: 10.1016/j.ejsobi.2006.07.034 8104 G.J. Measey 1 European Jal/mal ofSail Biology 42 (2006) SI03-8110 the taxa concemed special searching methods are result) most soil herpetofauna appear to be concentrated required which should be standardised for comparative in the upper layers of the soil and its associated litter. It purposes. Including searches which provide estimates is for these reasons that a sensu lato definition of soil of soil herpetofauna presence or abundance would (see above) is seen as the most appropriate to adopt. It increase the value of biodiversity surveys in the soil is recognised that as more, particularly ecological, ecosystem. Wolters [12] noted that alteration in species information becomes available on these groups, better composition is probably not a random process, and it working definitions may appear. may be that soil herpetofauna (and amphibians in parti All orders of Amphibia have soil dwelling represen cular) as top predators might act as indicators of wider tatives and one, the Gymnophiona or caecilians, are problems in the soil community, just as they are known almost entirely made up of limbless, tropical, subterra to do in terrestrial and aquatic systems [13]. nean species (Table 1). Many salamanders (Caudata) The purpose of this contribution is to: 1. Provide an are soi1 dwelling for part of their lives, and sorne appreciation of the biodiversity of soil herpetofauna, frogs regularly burrow into the soil, leaving this refuge with a preliminary attempt at quantification of the num for on1y relatively short periods [19]. The global distri ber ofspecies; and 2. to critically compare the results of bution of amphibians has recent1y been discussed, with semi-quantitative and quantitative soil herpetofauna the majority of species being found within the forested biodiversity surveys in order to move toward a standard tropics [20]. methodology. Among the Reptilia only the arder Squamata is con sidered here. No members of the arder Crocodilia are 2. An appreciation of the biodiversity of soil recognised as being primarily subterranean, despite herpetofauna constructing burrows. Tuatams (arder Rhynchocepha lia) inhabit burrows and occasionally eat soil macro At first inspection, two soil herpetofauna groups fauna but the majority of prey are not of subtermnean appear to be separated ecologically: those which use or leaf litter origin. Sorne tortoises and turtles (arder the soil (sensu lato, including leaf litter, wood, etc. Testudines), especially within the family Testudinidae, [2]) as a refuge (often for aestivation, or diel!noctumal construct and inhabit burrows, although as none eat soil refuge with relatively stable tempemture, pH, humid macrofauna (instead foraging herbivorously on the sur ity), and those which are truly s!1btermnean for the face) they are also excluded from this discussion. majority of their lives, reproducing in the soil, eating Table 1 highlights several groups which are exclu soil macrofauna, and rare1y reaching the surface. How sively subterranean, in particular the amphisbaenians ever, the two groups are not so easily differentiated, especially when the life history of most soil herpeto and scolocophidian snakes. Another reason why biodi fauna is unknown. Intermediary forms are known versity ofsoil herpetofauna is often underappreciated is (subtermnean-terrestrial or subtermnean-aquatic [14, the superficial resemb1ance of sorne forms due to their 15]) which makes the assessment even more ·difficult. subterranean lifestyle (Fig. 1). Many species have Use of the soil may also be related to ontogeny [15], undergone body elongation, lost limbs, have similar and to complicate matters further, there are certain spe feeding mechanics, skin and scale structure, and cies which appear to be flexible enough to be either changes in sensory systems (e.g. reduction of eyes completely subtermnean or predominant1y epigeic and covering of orbit, Fig. 1) These superficial resem depending on the habitat in which they are found blances are partly responsib1e for inappropriate taxo [16]. That notwithstanding, the inclusion of these taxa nomie determinations as even closely related species within soil fauna is demonstmted by their dependence may appear similar morphologically. on soil macroinvertebrate prey items [16-18]. Difficulties in taxonomy, lack ofsufficient sampling, Given these difficulties and the overwhelming lack and an inadequate understanding of ecology are prob ofecological data on the majority ofspecies involved, it ably the major impediments to determining an accurate is doubtful that working definitions separating groups estimate for the total biodiversity of soil herpetofauna. are useful. However, it is important to bear in mind that More important1y, it is considered that these are more there is almost certainly a gradation of life styles extreme in soil dwelling species than their terrestrial or between the extremes of animaIs which rare1y enter aquatic counterparts. Hence both proportions and num the soil (sensu stricto), and those that mrely leave it. bers of species given in Table 1 are thought to be con Rather like their soi1 macrofauna prey (or perhaps as a servative estimates. G,J. Measey 1 European Journal ofSoi! Biology 42 (2006) S103-S110 SI05 Table 1 Numbers ofsoil dwelling species ofsquamate reptiles and amphibians, Taxonomy and species numbers were taken from AmphibiaWeb (http://elib, cs,berkeley.edulaw/- accessed 10-08-04) and Animal Diversity Web (http://animaldiversity.urnrnz.umich.edu - accessed 10-08-04). See text for criteria of inclusion in soil vertebrates Taxon Common name Soil dwe11ing Total species Percent soil species dwelling RePTILIA Reptiles Order Squamala 2209 7879 28.0 Suborder Sauria Lizards Gekkota Geckos, blind lizards and legless lizards 50 1101 4.5 Diploglossa Glass lizards, American legless lizards, 103 117 88.0 knob-scaled lizards, etc Iguania 19uanas, chameleons, anoles, etc 0 1633 0.0 Platynota Monitor lizards 0 57 0.0 Scincomorpha Skinks, whiptails, night lizards, etc 1244 1919 64.8 Suborder Amphisbaenia Worm lizards 158