Mastozoología Neotropical ISSN: 0327-9383 [email protected] Sociedad Argentina para el Estudio de los Mamíferos Argentina
Cajal, Jorge; Tonni, Eduardo P.; Tartarini, Viviana THE EXTINCTION OF SOME SOUTH AMERICAN CAMELIDS: THE CASE OF Lama (Vicugna) gracilis Mastozoología Neotropical, vol. 17, núm. 1, enero-junio, 2010, pp. 129-134 Sociedad Argentina para el Estudio de los Mamíferos Tucumán, Argentina
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THE EXTINCTION OF SOME SOUTH AMERICAN CAMELIDS: THE CASE OF Lama (Vicugna) gracilis
Jorge Cajal1, Eduardo P. Tonni2, and Viviana Tartarini2
1 Fundación para la Conservación de las Especies y el Medio Ambiente (FUCEMA), Av. de Mayo 1190, 2º piso, 1085 Ciudad Autónoma de Buenos Aires, Argentina [Corresponding author: Jorge Cajal
ABSTRACT. Lama (Vicugna) gracilis (Gervais and Ameghino, 1881) is a Camelidae that inhabited the low plains of Argentina and Uruguay during the Pleistocene and early Ho- locene. Considering that Lama gracilis was a vicariant of L. vicugna in the low plains, sympatry cases between Lama guanicoe and Lama vicugna are analyzed to test the hy- pothesis that considers the competence for the same resource as the cause of extinction of Lama gracilis. It is concluded that the reduced populations of L. gracilis were forced to extinction especially by hunting pressure of paleoindian groups.
RESUMEN. La extinción de algunos camélidos sudamericanos: el caso de Lama (Vicugna) gracilis. Lama (Vicugna) gracilis (Gervais y Ameghino, 1881) es un camélido que habitó las planicies bajas de la Argentina y Uruguay durante el Pleistoceno y el Holoceno temprano. Considerando que Lama gracilis fue un vicariante de L. vicugna en las planicies bajas, se analizan los casos de simpatría entre Lama guanicoe y Lama vigugna para poner a prueba la hipótesis que considera la competencia por el mismo recurso, como la causa de la extinción de Lama gracilis. Se concluye que las poblaciones reducidas de L. gracilis fueron forzadas a la extinción por la presión de caza de grupos paleoindios.
Key words. Camelidae. Extinction. Pleistocene. South America.
Palabras clave. América del Sur. Camelidae. Extinción. Pleistoceno.
Although there is no consensus among authors Patagonian and Pampean regions. These au- regarding the taxonomic status of living South thors consider the guanaco as a single species American camelids, there is agreement in rec- included in the subgenus Lama: Lama (Lama) ognizing two wild species: the guanaco, Lama guanicoe, and the vicugna as a subgenus of guanicoe Müller, 1776, and the vicuña Lama including two species, the living one Vicugna vicugna (Molina) Miller, 1924 (or Lama (Vicugna) vicugna (Molina, 1782) and Lama vicugna Molina, 1782; for a recent dis- the extinct Lama (Vicugna) gracilis (Gervais cussion from a molecular and chromosomal and Ameghino, 1881). They conclude that point of view, see Marín et al., 2007). Lama (V.) gracilis and Lama (V.) vicugna are Menegaz et al. (1989) reframed the tax- more closely related to each other than with onomy of the genus Lama through a multi- Lama (Lama) guanicoe. variate morphological and morphometric study, Recently, Weinstock et al. (2009) sustained including the modern South American that “In light of the combined genetic and mor- Camelidae and those of the Pleistocene of the phological arguments discussed above, we
Recibido 7 noviembre 2008. Aceptado 27 junio 2009. Editor asociado: L Borrero 130 Mastozoología Neotropical, 17(1):129-134, Mendoza, 2010 J Cajal et al. http://www.sarem.org.ar argue that the fossil remains assigned to L. province) there is a stratigraphic association gracilis probably belong to V. vicugna…” In between L. guanicoe and L. gracilis in the any case, it should be noted that molecular middle Pleistocene (< 0.78 Ma and > 0.126 analysis, based on few genetic markers (e.g. Ma) of the Reconquista River. In the late Pleis- from mt DNA) not always match fossil records tocene, this association is verified in Paso (see Cajal, 2006; Marin et al., 2006). Otero (Necochea County), in the La During the late Pleistocene and early Ho- Chumbiada and Guerrero members of the locene, Lama gracilis inhabited the Patagonian Luján Formation. The Guerrero Member was region and east of the Pampean region. Out- dated between ca. 24 000 and ca. 10 000 ra- side Argentina, there are records in Uruguay diocarbon years BP (Tonni et al., 2003), for the late Pleistocene before 40 000 radio- whereas the La Chumbiada Member seems to carbon years BP (Ubilla, 2004) and for the be older than 35 000 radiocarbon years BP early Holocene (10 480 to 11 090 radiocarbon (L. Pomi, personal communication 2008), be- years BP; cited as Lama sp. by Ubilla et al., ing its temporal extension unknown. 2007; M. Ubilla personal communication, 2008). The vicuña has a poor palaeontological In Argentina, L. gracilis is stratigraphically record, restricted to the areas of its modern associated to L. guanicoe at least in four sites distribution; the oldest records are that of the locations of the Santa Cruz Province: La María Atacama dessert, Chile, with a radiocarbon (10 967 ± 55 radiocarbon years BP, Paunero, dating of 11 700 radiocarbon years BP (Kuch 2002), Los Toldos (12 600 ± 650 radiocarbon et al., 2002) and between 12 600 and 10 200 years BP; Cardich et al., 1973; Cardich, 1987), cal. year BP (Grosjean et al., 2005). El Ceibo (ca. 11 000 radiocarbon years BP; In this paper, the cases of sympatry between Cardich, 1987) and Piedra Museo (units 6 to L. guanicoe and L. vicugna are taken as mod- 4, dated between 12 890 ± 90 and 9230 ± 105 ern analogues to test the hypothesis which radiocarbon years BP; Miotti and Salemme, considers the competition for the same resource 2003). In the Chilean sector of the island of as the cause for the extinction of L. gracilis. Tierra del Fuego, in the site Tres Arroyos 1, Today, the vicugna inhabits the high plains one mandibular symphysis referred to Vicugna or Andean altipampas from northern Peru, sp. by Prieto and Canto (1997) probably per- Western Bolivia, North-Eastern and Central tains to L. gracilis; it is stratigraphically asso- Chile, and North-Western Argentina down to ciated to L. guanicoe in a level dated 10 630 the north region of San Juan Province (Cajal, ± 90 radiocarbon years BP (Massone and 1991). In Argentina, it inhabits the Puna and Prieto, 2004). This radiocarbon date is a taxon- high-Andean areas contiguous with the Puna. date obtained on bone collagen, and it is simi- The vicuña has three levels of occupation in lar to other three taxon-dates obtained on L. the territory with respect to the guanaco: a) guanicoe bones from the site Cueva del Medio altitudinal segregation, where there is no over- (10 450 ± 100, 10 710 ± 190, and 10 850 ± lap between both species (in Peru, northeast 130 radiocarbon years BP; see Nami and of Bolivia, north of Chile –from 8º to 20º S; Nakamura, 1995). In the great majority of b) they share the altitudinal level but with in- cases, in which not taxon-dates proved the cipient spatial segregation, in Tarija (Bolivia), coexistence of both species, the stratigraphical Sierras de Zenta, Santa Victoria, Chañi and association averaged a short period of time. Lipán, in Jujuy, Abra de Acay in Salta and Consequently, it is considered as coeval in a high-Andean areas (excluded de Puna stricto broad sense. In all these sites, the remains of sensu) in Catamarca; c) high superposition L. guanicoe are always dominant over those degree (sympatry), in the altipampas of a fringe of L. gracilis. of the Cordillera Frontal between 27º 56’ S According to the information given by and 29º 35’ S. Menegaz et al. (1989) and new findings, at Studies performed during four consecutive the east of the Pampean region (Buenos Aires years (1978-1984) in the Cordillera Frontal, EXTINCTION OF SOUTH AMERICAN CAMELIDS 131
San Juan Province, demonstrated that both the cantly different way, while in others, differ- vicuña and the guanaco showed a constant ences were not observed. According to Q pattern relative to the mean size of their re- values of this method, the vicuña turned out spective family groups, social structure, terri- more sensitive than the guanaco with respect torial behaviour (intra and interspecific), and to the different sectors (Cajal, 1989). It should population increase (census number per years). be noted that two species by definition have These species also display a high degree of always differences, regardless how close re- diet overlap, and to some extent of spatial use, lated they are. regardless of the differences in the pattern of The body mass of L. gracilis estimated with habitat use and preference of sectors accord- regression equations for artiodactyls (Scott, ing to the social group and time of the year 1990), based on the transverse width of the (Cajal, 1989, Cajal and Bonaventura, 1998). head of the humerus and maximum width of In the sympatry area, both guanacos and the distal epiphysis, is between 50.36 and 64.32 vicuñas are clearly grazers (although they also kg. Hence, its mass is similar to that of the browse on bushes and cactaceae). According vicuña (45-55 kg) and quite different from that to Cajal (1989), in the case of the vicugna the of the guanaco (80-120 kg). grass represents 88% and shrub / cacti 12% of Both L. gracilis and the vicuña show dental diet, while in guanaco the grass represents 87% specializations for abrasive grasses (i.e., Stipa). and shrub / cacti 13% of diet. Coexisting wild Functionally, the dental specialization of inci- camelids respond in the same way when fac- sors in both species (see Menegaz et al., 1989) ing the available food at a given place and tends to optimize the intake of abrasive grasses time (e.g. Stipa grass). Certainly, the genus (pastures) with high silica content. In this re- Stipa is the main component of the diet of gard, a positive correlation has been mentioned both species. A test of multiple comparisons between silica and palatability (Adler et al., among plant species ordered according to the 2004). amount of their mean frequency in the diet L. gracilis inhabited, during the late Pleis- showed that Stipa is in both camelid species, tocene and early Holocene, the low plains from the most important group, clearly distinguished the Pampean region to Patagonia. Considering from other plants (Cajal, 1989). This larger that the oldest records belong probably to the presence of Stipa in the respective diets is middle Pleistocene of the Pampean region, related to supply. Within perennial plants, this Menegaz et al (1989:170-171) postulated a genus is outstanding by its larger percentile southward retraction of L. gracilis during the presence (> 40 %) when analyzing the plant late Pleistocene. There are no evidences to cover of the high plain (altipampas) or steppes confirm this hypothesis, since in Patagonia of the region. there is no paleontological record of the late The physiography where the vicuñas and Pleistocene prior to ca. 12 000 years BP. L. guanacos are sympatric is like a high plains gracilis seems to have followed the expansion archipelago originated by ravines, creeks, riv- of the Pampean fauna toward the end of the ers, and mountains. This configuration defines Pleistocene –around 12 000 years BP, as veri- limited areas or sectors. A comparative analy- fied with several species present in both re- sis of the use of these sectors by both species gions during that period (Borrero, 1999, 2005; (test of equality of means with heterogeneous Tonni and Carlini, 2008). variances using the Games and Howell method, Menegaz et al (1989) pointed out that post- MCHETV, see Sokal and Rohlf, 1981), re- glacial climatic changes affected the distribu- vealed that for both, the guanaco and the tion of different groups of Grammineae and vicuña, some sectors were significantly differ- influenced deeply in the retraction and extinc- ent to others, while others did not show such tion of L. gracilis. In this sense, they suggest differences. Considering both species as a that the present distribution of L. vicugna is block, some sectors were used in a signifi- related to that of microthermal grammineae 132 Mastozoología Neotropical, 17(1):129-134, Mendoza, 2010 J Cajal et al. http://www.sarem.org.ar groups, especially to those best adapted to arid ternary, caused a decrease of the biomass of environments, rather than to those specialized the mammals adapted to open areas. These to life in mountains. On the contrary, the gua- authors indicate that the studies based on naco is a generalist herbivore, adapted to a geochemical and dust proxies in Greenland, wide range of vegetation and habitats, which Antarctica, and South America glaciers attest places it, according to some authors, out of that the present interglacial period is not sub- the competence with other herbivores of this stantially different from the preceding ones. size (Raedeke and Simonetti, 1988). The arrival of humans in South America was According to Menegaz et al. (1989) the the sole new biological or geological event extinction of L. gracilis was caused by an that occurred in the present interglacial pe- unfavourable competence with the guanaco in riod. In consequence, the entrance of men and the exploitation on similar niches (Menegaz et their pressure on a numerically reduced popu- al., 1989:171), being the competence a causal lation would have been the factor that led to source of extinction. However, using a mod- local extinction (extirpation) or total (global) ern analogue, in sympatry, both guanacos and extinction. The different extinction of related vicugnas feed on the same food resources. If species (e.g., between Cervidae and Camelidae, resources are scarce, competition may be the cited by Cione et al., 2009), may correspond outcome of shared limiting resources. It does to subtle differences in ecological plastic- not matter who ate the food if it is gone. The ity. shortage can affect the individuals of both If L. gracilis –unlike the guanaco–, had en- species as a whole. There is no evidence for vironmental sensitivity and strict trophic and competition at that time and place in the Cor- habitat requirements, similar to those of the dillera Frontal. However, it does not indicate vicuña in modern high plains, the climatic that competition between individuals of the change in low plains (Tonni et al., 1999) could same species and between those of both spe- have reduced their populations up to levels in cies occurs when food resources are scarce. which hunting pressure of paleoindian groups Neither does it mean that the competition led them to extinction. caused by food scarcity necessarily implies the Alternatively, if it is proved that L. gracilis displacement (or extinction) of one species by and L. vicugna (or Vicugna vicugna) are the the other; nor that it is a factor involved in same species (see Weinstock et al., 2009), the future evolutionary changes. local extinction in the low areas and their re- Other causes that led to extinction must be traction to regions of the high plains or Andean considered, beyond the interspecific compe- altipampas, can be attributed also to the tence. One of them is the hunting burden ex- anthropic action that not only includes the hunt erted by paleoindians, a hypothesis taken to burden but also other factors (i.e., environ- an extreme by Martin (1984) in his model of mental change and etological changes caused blitzkrieg, as the cause of massive extinction by the human presence). of the end of the Pleistocene in North America, and by extension, in South America. Acknowledgements. The authors are grateful to Agencia The zooarchaeological records demonstrate Nacional de Promoción Científica y Tecnológica, Comisión de Investigaciones Científicas de la provincia the effects of hunting pressure on camelids, de Buenos Aires, and Universidad Nacional de La Plata both in guanaco and L. gracilis. However, the for financial support. relative frequency of the remains indicates a bias towards the first species with respect to LITERATURE CITED the second. 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