|Scientific Name:||Chelonoidis becki (Rothschild, 1901)|
Chelonoidis becki (Rothschild, 1901)
Chelonoidis nigra ssp. becki (Rothschild, 1901)
Geochelone becki (Rothschild, 1901)
Geochelone elephantopus ssp. becki (Rothschild, 1901)
Geochelone nigra ssp. becki (Rothschild, 1901)
Testudo becki Rothschild, 1901
|Taxonomic Source(s):||Fritz, U. and Havas, P. 2007. Checklist of chelonians of the world. Vertebrate Zoology 57(2): 149-368.|
|Taxonomic Notes:||The previous Red List assessments for Galápagos tortoises treated the various allopatric island populations as subspecies of Chelonoidis nigra (now named Chelonoidis niger), as did several authors (Pritchard 1996, Caccone et al. 1999, Beheregaray et al. 2003, Fritz and Havas 2007, TTWG 2007, Rhodin et al. 2008). However, other authors have considered them as full species based on morphology (Bour 1980, Fritts 1983, Ernst and Barbour 1989) and the more recent consensus among researchers (Caccone et al. 2002; Russello et al. 2005, 2007; Poulakakis et al. 2008, 2012, 2015; Chiari et al. 2009) is to treat most as full species based on congruent patterns of mitochondrial and nuclear variation. This elevated species-level taxonomy has been largely accepted by TTWG (2009, 2014) and TEWG (2015) for most, but not all, phylogenetic lineages of Galápagos tortoises. This Red List assessment therefore now treats C. becki as a full species, rather than retaining its previous subspecies ranking from earlier Red List assessments.
Chelonoidis becki has generally always been considered a distinct taxon based on its isolated occurrence on Wolf Volcano on northern Isabela, consistent also with prior recognition of the other tortoise populations on central and southern Isabela volcanoes as distinct taxa: microphyes, vandenburghi, guntheri, and vicina. However, as population morphologies were considered, the dome-shaped central and southern Isabela populations were merged by Pritchard (1996) into a broader vicina taxon, into which microphyes, vandenburghi, and guentheri [= guntheri] were synonymized. Later genetic analysis demonstrated that all southern Isabela populations are very closely related to each other, with C. becki more closely related to C. darwini from Santiago (Poulakakis et al. 2012, 2015).
Chelonoidis becki includes two distinct genetic lineages, each of which occurs in nearly separate ranges: one on the eastern and northern slopes of Wolf Volcano associated with Piedras Blancas and the other on the southwestern slopes associated with Puerto Bravo (Garrick et al. 2014).Both of these lineages derived from tortoises from Santiago (C. darwini, Caccone et al. 1999, 2002; Garrick et al. 2014).
Genetic data indicate the presence on Wolf Volcano of hybrid individuals from species from distant islands (C. niger [Extinct], C. abingdonii [Extinct], and C. hoodensis), as well as the presence of hybrid individuals with species from the same island. The first ones, and possibly all, are likely to have arrived on Wolf Volcano because of human activities, while those from other volcanoes of Isabela are the possible results of sporadic tortoise dispersal events from one volcano to the next by land (from Darwin Volcano) or by sea from the central (Alcedo Volcano) or southern (Sierra Negra and Cerro Azul) Isabela volcanoes (Beheragaray et al. 2007).
The carapace morphology of Wolf Volcano tortoises is quite variable, with carapace shapes ranging from domed to intermediate to saddlebacked Given that the ancestor of this species is C. darwini from Santiago (Caccone et al. 1999; Caccone et al. 2002; Poulakakis et al. 2008, 2013; Garrick et al. 2012, 2014), a species with an intermediate carapace shape, we assume that this is the ancestral carapace shape for C. becki, whereas the presence of domed and saddlebacked individuals is likely the result of past mating events with individuals from other islands (see above).
|Red List Category & Criteria:||Vulnerable A1bde ver 3.1|
|Assessor(s):||Caccone, A., Cayot, L.J., Gibbs, J.P. & Tapia, W.|
|Reviewer(s):||Rhodin, A.G.J. & van Dijk, P.P.|
|Contributor(s):||IUCN Galapagos Tortoises Red Listing Workshop & Galapagos National Park Directorate|
|Facilitator/Compiler(s):||van Dijk, P.P.|
While historic and recent population estimates are quite imprecise, even the best-case scenarios indicate a population collapse of well over half from historical levels less than three generations ago (at a generation time of 60 years), resulting primarily from past exploitation and, more recently, occasional poaching, qualifying the Wolf Volcano Tortoise as Vulnerable, VU A1bde. This species was previously assessed for the Red List in 1996 as Chelonoidis nigra ssp. becki (VU D1+2). This assessment also incorporates knowledge contributions from participants of the international workshop on Galápagos tortoises convened by the Galápagos National Park Directorate in July 2012.
|Previously published Red List assessments:|
Chelonoidis becki occurs on the northern, western, and southwestern slopes of Wolf Volcano, with a small group on an isolated plateau inside the crater, northern Isabela (formerly Albemarle Island) in the Galápagos Islands of Ecuador (Pritchard 1996). The northeastern and eastern slopes are little explored. The potential range of C. becki comprises about 263 sq. km.
|Range Map:||Click here to open the map viewer and explore range.|
Based on an estimated average density of one tortoise per hectare of suitable habitat, the historical population size may have been about 25,000 adults (J.P. Gibbs unpubl. data). In the early 1970s, the population was estimated at 1,000-2,000 tortoises (MacFarland et al. 1974). Currently, the population comprises at least 2000 marked adults (Garrick et al. 2012, 2014; Edwards et al. 2013), and is thought to include 7,000-8,000 animals (W. Tapia, pers. comm.).
|Current Population Trend:||Unknown|
|Habitat and Ecology:|
Chelonoidis becki is a large insular tortoise with an intermediate domed to slightly saddlebacked carapace with a vegetarian diet, adapted for grazing on low-growing vegetation as well as browsing on higher-growing vegetation in drier shrubland ecosystems. While detailed life history information is not available for wild animals, by analogy with captive animals and other Galápagos tortoises it is likely to mature at an age of 20 years or later, with an estimated generation time of 60 years.
|Generation Length (years):||60|
|Use and Trade:||
There is no direct evidence of exploitation of Wolf Volcano tortoises by 19th century whalers (Pritchard 1996). However, although access to interior populations may have been difficult, tortoises ranged (and still do) to the shoreline and would have been vulnerable to whalers. Recent reports of finds of slaughtered animals indicate some ongoing exploitation, possibly by illegal fishers (Cayot and Lewis 1994).
Galápagos Tortoises were decimated by overexploitation by humans for food, both by sailors taking tortoises on board as food supply, as well as by local settlers. While there is no known documented evidence of this for Chelonoidis becki, it is probable that the population was also exploited. Occasional poaching of tortoises has occurred in the last 25 years. The depleted C. becki population was potentially further impacted by the effects of introduced species, including rats, mice, cats, and goats (eradicated in 2006). In addition, eruptions of Wolf Volcano pose an unpredictable risk to tortoises due to their restricted occurrence on the southern and eastern flanks of the volcano. Genetic data suggest that the two genetically distinct subpopulations of tortoises of C. becki now residing in Piedras Blancas (northern) and Puerto Bravo (western) may be fusing back together due to lava flow changes resulting in tortoise trails between these two areas. As this is believed to be the result of natural processes, no conservation management of these two lineages is required (Garrick et al. 2014).
Legislation & regulations: Chelonoidis becki is protected under Ecuadorian national law. It has been included in Appendix I of CITES since 1975, prohibiting all forms of commercial international trade. Nearly all of Isabela including 100% of Wolf Volcano, and thus the entire native range of C. becki, are protected as part of the Galápagos National Park. Goat eradication from the three northern volcanoes of Isabela was confirmed in 2006. Conservation actions needed: further genetic analysis, removal of hybrid tortoises with high conservation value (to be used in breeding programs for other islands), and continued population monitoring and control of poaching.
Beheregaray, L.B., Ciofi, C., Caccone, A., Gibbs, J.P. and Powell, J.R. 2003. Genetic divergence, phylogeography and conservation units of giant tortoises from Santa Cruz and Pinzón, Galápagos Islands. Conservation Genetics 4: 31–46.
Beheregaray, L.B., J.P. Gibbs, N. Havill, T.H. Fritts, J.R. Powell, and A. Caccone. 2004. Giant tortoises are not so slow: rapid diversification by recent volcanism in Galápagos. PNAS 101: 6514-6519.
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|Citation:||Caccone, A., Cayot, L.J., Gibbs, J.P. & Tapia, W. 2017. Chelonoidis becki. The IUCN Red List of Threatened Species 2017: e.T9018A82426296.Downloaded on 18 January 2018.|