The Guanaco (Lama guanicoe)
Figure 1. A lone Guanaco (Lama guanicoe) in the Patagonian highlands
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Taxonomy
The Guanaco (Lama guanicoe) is one of two extant wild species of camelid native to the Americas and the direct ancestor of the llama (Lama glama)(2). The guanaco’s closest relative is the vicuña (Vicugna vicugna) from which it diverged about 2.5mya according to genetic studies. A single congeneric species has been suggested, Lama gracilis from the late pleistocene, but this species has since been shown to be synonymous with the vicuña (12). Amongst extinct relatives the guanaco groups with the other New World camels (Lamini) including the Pleistocene genera Palaeolama, Camelops, and Hemiauchenia (10). The guanaco is probably derived directly from Hemiauchenia, a population of which likely migrated to South America during the Great American Biological Interchange in the Pliocene and gave rise both extant species of South American camelids (10). Hemiauchenia is therefore considered paraphyletic with respect to the guanaco, as it is also represented by three late pleistocene species: H. gracilis, H. macrocephala, and H. paradoxa. (10).
Traditionally the guanaco has been subdivided into four subspeces: L. g. cacsilensis, L. g. guanicoe, L. g. voglii and L. g. huanacus, though a recent molecular study showed the latter two to be invalid (4). L. g. cacsilensis appears paraphyletic with respect to L. g. guanicoe (2, 4) and gene flow readily occurs (6) even so the two subspecies are found in distinct geographic regions (6). The llama probably arose out of a population of Lama guanicoe cacsilensis, as it clusters within this population (2). A third unnamed subspecies seems to have existed in Patagonia during the very late Pleistocene and early Holocene, but has since gone extinct (14).
Distribution and Population
Guanacos range from the South American tip to central Bolivia along the eastern foothills of the Andes mountains, as well as Patagonia and the Western foothills of the Andes in Peru (1). The IUCN assesses the species as Least Concern (1), with the bulk of the population residing in Argentina and southern Chile (1) belonging to the sub-species L. g. guanicoe. L. g. cacsilensis is restricted to a much smaller population in Peru and Northern Chile (6), these two sub-species intermix in an intermediate ‘contact zone’ (6).
Fossils recognizable as guanaco date back as far as the Late Pliocene (6). Remains from the Pleistocene indicate that the species was present throughout the pampas region as far north as Southern Brazil (6) and a few specimens have even been found in North-East Brazil (6) . Interestingly, it appears that the expansion into Patagonia and southern Chile was recent, around the last glacial maximum (6), which may be a response to a warming in the climate, an opening of niches after the extinction wave, or both. Today it is estimated that only about 5% of the initial population in less than 30% of the original range remains (6). This appears to have been a steady decline over the last thousand years, with an accelerated decline after the arrival of Spanish settlers (2), this has variously been attributed to overhunting, habitat loss, and the introduction of Old world livestock (6).
Fig 2. The current range and the range inferred from fossil sites of the Guanaco (Lama guanicoe). Fossil data from Palaelobiology database. Samples of habitat within the range are included.
Ecology
Guanacos typically attain a weight of 80-110kg making it a medium-sized camelid (Loponte & Corriale 2019). It is a hardy species, capable of surviving in a wide range of habitats, ranging from sea level to 4.5km altitudes and thriving in dry open habitats, though also inhabiting the Patagonian woodlands. They are resilient to a wide temperature range of below freezing to 45˚C. Their diet appears equally flexible with some populations being almost exclusively grazers and others primarily browsers depending on vegetation availability, though grazing is preferable when resources are abundant (5). The guanaco if present in Patagonia would have co-occurred with a plethora of large herbivores during the Late Pleistocene, the chief herbivores were the vicuña (Vicugna vicugna), the equid Hippidion principale, and giant ground sloth Mylodon darwinii (13). In the pampas, many more species would have been present, including Macrauchenia, Toxodon, Megatherium, Glyptodon. The diet of the guanaco at this time is unclear, but given its generalist role, it may have taken an opportunistic role in filling in locally vacant niches.
They form polygynous family groups ranging from 2-14 adult individuals, though males lacking females will form bachelor groups up to 75 individuals (8). The tendency to form groups appears to be linked heavily to predator detection, as members will be able to take turns looking out for threats whilst feeding (7). The main predator in question today is the Cougar (Puma concolor), though a large number of extinct predators probably preyed on the guanaco, only Puma concolor and Dusicyon avus are likely the most common given their size classes and large range overlaps(2). Juveniles are also predated by smaller canid species such as the Culpeo (Lycalopex culpaeus)(11). Humans also have a history of exploiting the guanaco during the Holocene, in fact it was probably the primary prey species for hunter-gatherers in Patagonia during this period (9, 14) and was a key driver of human population concentration (9, 14).
Citations
1. Baldi, R.B., Acebes, P., Cuéllar, E., Funes, M., Hoces, D., Puig, S. & Franklin, W.L. 2016. Lama guanicoe. The IUCN Red List of Threatened Species 2016: e.T11186A18540211. http://dx.doi.org/10.2305/IUCN.UK.2016-1.RLTS.T11186A18540211.en
2. Fan, R., Gu, Z., Guang, X., Marin, J. C., Varas, V., Gonzalez, B. A., Wheeler, J. C., Hu, Y., Li, E., Sun, X., Yang, X., Zhang, C., Gao, W., He, J., Munch, K., Corbett-Detig, R., Barbato, M., Pan, S., Zhan, X., Bruford, M. W., Dong, C.. (2020). Genomic analysis of the domestication and post-Spanish conquest evolution of the llama and alpaca. Genome Biology 21, 159.
3. Faurby, S., Pedersen, R. Ø., Davis, M., Schowanek, S. D., Jarvie, S., Antonelli, A., & Svenning, J.C. (2020). PHYLACINE 1.2.1: An update to the Phylogenetic Atlas of Mammal Macroecology. doi:10.5281/zenodo.3690867
4. Gonzalez, B. A., Palma, R. E., Zapata, B., Marin, J. C.. (2006). Taxonomic and biogeographical status of guanaco Lama guanicoe (Artiodactyla, Camelidae). Mammal Review 36(2), 157-178.
5. Loponte, D., Corriale, M. J.. (2019) Patterns of Resource Use and Isotopic Niche Overlap Among Guanaco (Lama guanicoe), Pampas Deer (Ozotoceros bezoarticus) and Marsh Deer (Blastocerus dichotomus) in the Pampas. Ecological, Paleoenvironmental and Archaeological Implications. Environmental Archaeology 25(4), 411-444.
6. Marin, J. C., Gonzalez, B. A., Poulin, E., Casey, C. S., Johnson, W. E.. (2012). The Influence of the arid Andean high plateau on the phylogeography and population genetics of guanaco (lama guanicoe) in South America. Molecular Ecology 22(2), 463-482.
7. Marino, A., Baldi, R.. (2008). Vigilance Patterns of Territorial Guanacos (Lama guanicoe): The Role of Reproductive Interests and Predation Risk. Ethology 114(4), 413-423.
8. Marino, A., Baldi, R.. (2014). Ecological Correlates of Group-Size Variation in a Resource-Defense Ungulate, the Sedentary Guanaco. PLoS ONE 9(2): e89060
9. Rindel, D. D., Moscardi, B. F., Perez, S. I.. (2020). The distribution of the guanaco (Lama guanicoe) in Patagonia during Late Pleistocene-Holocene and its importance for prehistoric human diet. Sage Journals 31(4), 644-657.
10. Scherer, C. S.. (2013). The Camelidae (Mammalia, Artiodactyla) from the Quarternary of South America: Cladistic and Biogeographic Hypotheses. Journal of Mammalian Evolution 20, 45-56.
11. Silva, B., Root-Bernstein, M.. (2021) History of canids in Chile and impacts on prey adaptations. Authorea.
12. . Weinstock, B. Shapiro, A. Prieto, J. C. Marín, B. A. González, M. T. P. Gilbert, E. Willerslev.. (2009) The Late Pleistocene distribution of vicuñas (Vicugna vicugna) and the “extinction” of the gracile llama (“Lama gracilis”): New molecular data. Quat. Sci. Rev. 28, 1369–1373
13. Metcalf, J.L., Turney, C., Barnett, R., Martin, F., Bray, S.C., Vilstrup, J.T., Orlando, L., Salas-Gismondi, R., Loponte, D., Medina, M., De Nigris, M., Civalero, T., Fernandez, P.M., Gasco, A., Duran, V., Seymour, K.L., Otaola, C., Gil, A., Paunero, R., Prevosti, F.J., Bradshaw, C.J.A., Wheeler, J.C., Borrero, L., Austin, J.J. and Cooper, A.. (2016). Synergistic roles of climate warming and human occupation in Patagonian megafaunal extinctions during the Last Deglaciation. Science advances, 2(6), pp. e1501682.
14. Moscardi, B., Rindel, D.D. and Perez, S.I., 2020. Human diet evolution in Patagonia was driven by the expansion of Lama guanicoe after megafaunal extinctions. Journal of archaeological science 115, pp. 105098