Ryan C.J. Walker¹,²
¹Nautilus Ecology, 1 Pond Lane, Greetham, Rutland, LE15 7NW, UK
²Open University, Department of Life Sciences, Faculty of Science, Milton Keynes, MK7 6AA, UK
Madagascar supports one of the highest rates of endemism of anywhere in the world (Brooks, 2006) and like many other regions of high endemism, Madagascar has complex, often nonconcordant patterns of microendemism among taxa (Goodman & Benstead, 2005). This pattern of microendemism holds true for Madagascar’s four species of endemic tortoises, all facing considerable threats to their survival, on account of the specialised habitat requirement and ecology of each species. However, unlike some of the island’s other more charismatic fauna, such as the lemurs (Mittermeier et al., 1994; Jolly, 1966), there still remains a lack of applied research into the ecology and conservation status of Madagascar’s rare endemic tortoises, in particular the smallest genera, Pyxis. The Pyxis genera support two species: the flat tailed tortoise (Pyxis planicauda) and the spider tortoise (Pyxis arachnoides). It is the latter of the two that will form the focus of this paper. P. arachnoides has until recently been almost completely overlooked by the scientific and conservation community. Therefore, this work will detail the research undertaken on the species to date, the resulting conservation status of the species and finally describe some of the BCG funded research currently being undertaken to help protect this small cryptic species that inhabits a very restricted range within the Dry Coastal Forests of south west Madagascar.
History of published literature and resulting IUCN Red Listing status of Pyxis arachnoides
The understanding of the ecology and conservation status of P. arachnoides is still very much in its infancy, with to date only six published articles within the scientific literature (peer review scientific journals) devoted to detailing the biology, ecology or conservation status of the species. When compared against the remaining species of Madagascar’s tortoise taxa (Fig. 1), it becomes obvious that P. arachnoides has drawn the least attention and we know least about this species.
Fig. 1. Number of peer reviewed scientific articles published in scientific journals detailing the biology, ecology or conservation status for each of Madagascar’s four endemic tortoise species.
P. arachnoides was first described in 1827 by the eminent British zoologist and taxonomist Thomas Bell (Bell, 1827). Following this, for many years, the species only received the briefest of mention in any scientific literature on African tortoises or Malagasy taxa. Finally, a very brief summary of a field trip, recording basic morphometic data on carapace size for just 11 individuals was documented in French, in the Bulletin of the National Museum of Paris (Malzy, 1964). This report represents the first account detailing primary data from wild individuals since the species was first described.
It was not until 1981 that Roger Bour documented the suspected distribution of the species, basic biological characteristics and confirmation that the species did indeed consist of three subspecies: Pyxis arachnoides brygooi, Pyxis arachnoides arachnoides and Pyxis arachnoides oblonga (Bour, 1981). Twenty-four years passed before any other literature appeared in the peer reviewed scientific press. As a result of the indiscriminate poaching of P. arachnoides that subsequently flooded the international pet market with illegally exported individuals between 2000 and 2004, Walker et al. (2004) produced a piece of analytical work highlighting the problem. Thankfully, at around this time the species was up-listed from CITES Appendix II to Appendix I, resulting in significant positive changes in the regulation of the international trade of the species. However, some level of poaching still remains a problem (Pedrono, 2008). The following year Chari et al. (2005) reported a preliminary study into the genetic variation of the three subspecies contained within the species P. arachnoides, and confirmed Bour’s (1981) original reporting that there was genetic distinction between the three subspecies; however, within each subspecies there appears to be very low genetic variability.
Following this, the knowledge of the species developed somewhat, when during 2002-03 Walker and colleagues undertook, to date, the most comprehensive ecological study of the species, investigating seasonal variation in activity and establishing the population density estimate of a cohort of tortoises across a 13km² area of Southern Dry Forest in the Anakao region of south west Madagascar (Walker et al., 2007). The paper also reported anecdotal evidence that the species was coming under increased pressure from poaching in some regions of its range, was locally extinct in some areas and was also suffering from pressure resulting from habitat destruction.
Meanwhile, the IUCN Red Listing authorities were having difficulty assigning an IUCN Red Listing category for the species. As Table 1 shows the species remained classified as ‘Indeterminate’ up until the Red Listing Meeting of 1996, meaning that the species was thought to be facing threats to its long term survival, but these threats could not be quantified due to a lack of available data. This is in contrast to Madagascar’s largest species, the radiated tortoise Astrochelys radiata and the ploughshare tortoise Astrochelys yniphora; as Figure 1 shows, both species support the greatest body of literature of all of Madagascar’s tortoise taxa and consequently have been confidently assigned appropriate IUCN Red Listings since 1982 (Table 1).
Table 1. Current and historical IUCN Red Listing status for Madagascar’s four endemic tortoise species. Categories go in the following order: Least Concern (LC), Data Deficient (DD) or the pre 1994 listing of Indeterminate (IN), Near Threatened (NT), Vulnerable (VU), Endangered (EN), Critically Endangered (CR) and Extinct in the wild (EW). Source: IUCN’s web based Red Listing resource (Leuteritz & Rioux Paquette, 2008; Leuteritz & Pedrono, 2008; Leuteritz & Walker, 2008; Leuteritz et al., 2008).
This problem was finally beginning to be rectified as the sparse body of information began to grow slightly towards the end of the 1990s. Using more comprehensive published data sets has allowed increasingly stringent conservation status classifications to be assigned during the last two IUCN Tortoises and Fresh Water Turtle Specialist Group Planning Meetings in 1996 and 2008 (Table 1). Threats to the long term survival of this species, such as harvesting for food and the pet trade and habitat destruction, were suspected for many years and prompted the ‘Indeterminate’ status between 1982 and 1996. However, there were no quantitative data to back up these suspicions. But during the recent Madagascar Tortoise Conservation Planning and Red Listing Meeting in Antananarivo in January 2008 (Mittermeier et al., 2008), the current ‘Critically Endangered’ status based on the criteria of habitat destruction and harvesting for the food and the pet trade (A4cd; E) (Leuteritz & Walker, 2008) is now able to be made with reasonable confidence based on the data presented (Walker et al., 2007; 2004). This paper demonstrates, however, that we still have a long way to go before we have a full and completely comprehensive understanding as to the true conservation status and ecology of this species.
A small team of researchers with an interest in the conservation of P. arachnoides have developed a three year programme of research to investigate the exact status of the remaining wild populations of the species and further the knowledge of the ecology of the species. February and March 2009 marked the first field season in Madagascar, and during this time the team surveyed the entire range of the northern subspecies, P. a. brygooi. In addition to this, further ecological surveying was undertaken at the monitoring site documented in Walker et al. (2007). It was decided that it was important to establish a population density estimate for P. a. brygooi first, as it is considered to be the most threatened of the three subspecies (Ogle & Hudson, 2008).
This field work, funded in part by the BCG, undertook a comprehensive population survey using the Distance Sampling technique developed by Buckland et al. (2004). This method lends itself well to carrying out population estimates of tortoises. Fifty-eight 1km transects were traversed on foot in areas of the coastal Dry Southern Forest habitat across the complete suspected range of P. a. brygooi during February 2009 (Fig. 2). The work undertaken proved challenging and the thick, spiny vegetation across most of P. a. brygooi’s range (Fig. 3) has probably contributed in part to the lack of knowledge, on account of this challenging terrain making field work difficult.
Fig. 2. South west Madagascar. Suspected area of occurrence of P. a. brygooi (Pedrono, 2008; Bour, 1981), with survey locations overlaid.
Fig. 3. (a) Coastal Dry Forest, south west Madagascar. (b) P.a. brygooi in situ. Photos by R.C.J. Walker.
Ninety-six individuals were detected during the survey which spanned over 100km of coastal forest. The survey represented over 150 man-hours of surveying. A comprehensive population estimate is yet to be determined through statistical data analysis; however, we have established that the northern subspecies of P. arachnoides is threatened, with only four small, fragmented populations remaining (Fig. 2). The range begins 10km north of the port town of Toliara and stretches north to the Mangoky River estuary. The species inhabits a very narrow coastal strip of forest and is not recorded further than 8km inland. P. a. brygooiis suffering from anthropogenic habitat destruction attributed to charcoal production and stock grazing, and areas of good habitat are completely devoid of tortoises; there is also probable evidence of illegal collection for food by the local communities and collection for illegal export for the exotic pet trade. We are working with Conservation International (Madagascar) with the hope of implementing a long term monitoring programme for one of the last remaining populations of P. a. brygooi.
Unfortunately, due to the restricted range of P. a. bryooi, the species currently does not inhabit any protected areas. However, Madagascar’s government is in the process of tripling the country’s protected area network (Kramen et al., 2008), whereby two new protected areas are proposed within the range of P. a. brygooi (The Northern Mikea and the PK32 Ranobe Protected Areas). When our results are overlaid on the GIS of the proposed park boundaries, all of the last remaining viable populations of P. a. brygooi discovered in our survey fall outside the proposed boundaries of these protected areas. However, the author is working with WWF, the facilitating NGO charged with managing the new protected area proposals, in an effort to get some of the last remaining wild populations of P. a. brygooi included within the protected area boundaries.
It is hoped that in the coming two field seasons detailed population range and density estimates can be established for P. a. arachnoides and P. a. oblonga, and that these results can be incorporated into sound management policy in an effort to help protect this rare species.
In addition to BCG funding, the field work described in this paper was also financially supported by the Turtle Conservation Fund, the Turtle Survival Alliance and the Royal Geographic Society. Logistical support and help with field work was provided by Inge Smith, Charlie Gardener, Alice Ramsay Harison Randriansolo, Al Harris, Blue Ventures and our project partners MICET and the University of Antananarivo. Adviceon survey design was provided by Mike Gillman, Justin Gerlach andMandy Dyson.
Bell, T. (1827). On two new genera of land tortoises. Transactions of the Linnean Society of London 15: 392-401.
Bour,R. (1981). Etude systématique du genre endémique Malagache Pyxis Bell,1827 (Reptilia,Chelonii).Bulletin Mensuel de la Société Linnéenne de Lyon 50(4): 132-144; 50(5): 154-176.
Brooks, T.M., Mittermeier, R.A., da Fonseca, G.A.B., Gerlach, J., Hoffmann, J., Lamoreux, F.J., Mittermeier, C.J., Pilgrim, J.D., & Rodrigues, A.S.L. (2006). Global Biodiversity Conservation Priorities. Science 313(5783): 58-61.
Buckland, S.T., Anderson, D.R., Laake, J.L., Burnham, K.P., Borchers, D.L., & Thomas, L. (2004). Advanced Distance Sampling. Oxford University Press. 416 pp.
Chiari, Y., Thomas, M., Pedrono, M. & Veites, D.R. (2005). Preliminary data on genetic differentiation within the Madagascar spider tortoise, Pyxis arachnoides (Bell, 1827). Salamandra 41: 35-43.
Goodman, S. M. & Benstead, J.P. (2005). Updated estimates of biotic diversity and endemism for Madagascar. Oryx 39: 73-78.
Jolly, A. (1966). Lemur Social Behavior and Primate Intelligence. Science 153(3735): 501-506.
Kremen, C.A., Cameron, A., Moilanen, S.J., Phillips, C.D., Thomas, H., Beentje, J., Dransfield, B.L., Fisher, F., Glaw, T.C., Good, G.J., Harper, R.J., Hijmans, D.C., Lees, E., Louis Jr., R.A., Nussbaum, C.J., Raxworthy, A., Razafimpahanana, G.E., Schatz, M., Vences, D.R., Vieites, P., Wright, C. & Zjhra, M.L. (2008). Aligning Conservation Priorities Across Taxa in Madagascar with High-Resolution Planning Tools. Science 320: 222-226.
Leuteritz, T. & Pedrono, M. (2008). Astrochelys yniphora. In: IUCN 2008. 2008 IUCN Red List of Threatened Species. www.iucnredlist.org. Downloaded on 10 April 2009.
Leuteritz, T. & Rioux Paquette, S. (2008). Astrochelys radiata. In: IUCN 2008. 2008 IUCN Red List of Threatened Species. www.iucnredlist.org. Downloaded on 10 April 2009.
Leuteritz, T., and Walker, R. 2008. Pyxis arachnoides. In: IUCN (2008). 2008 IUCN Red List of Threatened Species. www.iucnredlist.org. Downloaded on 10 April 2009.
Leuteritz, T., Randriamahazo, H. & Lewis, R. (2008). Pyxis planicauda. In: IUCN 2008. 2008 IUCN Red List of Threatened Species. www.iucnredlist.org. Downloaded on 10 April 2009.
Malzy, P. (1964). Sur Pyxis arachnoides (Bell, 1827). Tortue terrestre du Sud de Madagascar. Bulletin of the Museum of Natural History, Paris. 36(4): 441-443.
Mittermeier, R.A., Rhodin, A.G.J., Randriamahazo, H., Lewis, R.E., van Dijk, P.P., Hudson, R., & Rioux Paquette, S. (2008). Vision sokatra gasy – Madagascar turtle vision. Turtle and Tortoise Newsletter 12: 7-9.
Mittermeier, R., Tattersall, I. & Konstant, W. (1994). Lemurs of Madagascar. Tropical Field Guide Series No. 1. Conservation International, Washington. 353 pp.
Ogle, M. & Hudson, R. (2008). Madagascar quest: 12 days to find four Pyxis. Turtle Survival Alliance Newsletter Aug. 2008: 40-42.
Pedrono, M. (2008). The Tortoises and Turtles of Madagascar. Natural History Publications (Borneo), Kota Kinabalu, Malaysia.
Walker, R.C.J., Rix, C., & Woods-Ballard, A.J. (2004). The legal and illegal trade in the Madagascar spider tortoise Pyxis arachnoides, for the exotic pet trade. Herpetological Bulletin 90: 2-9.
Walker, R.C.J., Woods-Ballard, A.J., & Rix, C.E. (2007). Population density and seasonal activity of the threatened Madagascar spider tortoise (Pyxis arachnoides arachnoides) of the southern dry forests, south west Madagascar. African Journal of Ecology 46: 67-73.
Testudo Volume Seven Number One 2009