High Potential for Competition Between Guanacos and Sheep in Patagonia

Abstract

Guanacos (Lama guanicoe) are the largest native Artiodactyl in South America and the most widely distributed. In arid Patagonia, densities are low and negatively related to domestic sheep numbers in space and time consistent with interspecific competition theory. Although guanacos and domestic sheep have been described as intermediate feeders sharing food resources, no studies have been conducted to compare their diets in sympatric conditions and explore whether the potential exists for direct interspecific competition. We assessed the diet of both species across 9 different sites and 2 seasons by microhistological analysis of fecal samples. We found that (1) guanacos and sheep are generalist herbivores feeding on a wide range of plant species; (2) both are intermediate feeders able to include both monocotyledoneous and dicotyledoneous plants in their diet; (3) both are able to change their diets seasonally; and (4) food niche overlap is high, particularly in summer when food resources are more scarce than in spring. We conclude that the potential for competition between guanacos and sheep is high and could have played a major role in the demise of guanacos. Consequently, current management practices focused on maximizing sheep numbers are not compatible with the recovery of guanaco populations.

Mulinum spinosum y la carne de cordero: detección de su presencia en ovinos vivos

“…Es una planta muy difundida como principal componente de la estepa herbáceo-arbustiva y sobre las laderas bajas desde San Juan y Mendoza hasta Santa Cruz en Argentina y desde Coquimbo a Magallanes en Chile, apareciendo a altitudes de 40-1500 m.s.n.m (Constance, 1988). Es la principal arbustiva de disponibilidad primavera-estival cuyos brotes, flores y frutos forman parte importante de la dieta de ovinos y caprinos en la región patagónica (Bonino et al, 1986;Somlo et al, 1981;Bonvissuto y Somlo, 1998) y de la fauna salvaje autóctona o asilvestrada como guanacos (Lama guanicoe) (Bahamonde et al, 1986;Baldi et al, 2004), chinchillón (Lagidium viscacia) (Galende et al, 1998) y ciervo colorado (Cervus elaphus) (Bahamonde et al, 1986).…”

Guanaco’s diet and forage preferences in Nothofagus forest environments of Tierra del Fuego, Argentina

“…Our results, however, highly contrast with guanacos' diet determined in other environments outside Tierra del Fuego. In continental Patagonia, for instance, it has been demonstrated that guanaco diet overlap with that of sheep during the summer season, when both species feed on grasses and grass-like species found in meadows (Baldi et al, 2004). During the winter months, instead, guanaco shifts its preference to shrubs (Senecio spp., Mulinum spp., Berberis spp.…”

“…On the other hand, the corporal mass plays an important role in the foraging strategy (Gordon, 2003). In this regard, it has been proposed that an inverse relationship exists between body size and selectivity, being the guanaco a herbivore with an intermediate selectivity (species from 50 to 200 kg of body weight (Baldi et al, 2004).…”

“…These facts make herbivores to select grazing areas of abundant and nutritionally good forage quality (Pelliza Sbriller et al, 1997). According to its feeding habits, guanaco (Lama guanicoe Müller), a native ungulate widely distributed in South America, may be considered a generalist of intermediate selectivity, since its diet include most of the plants present in its natural habitat (Baldi et al, 2004).…”

International Trade in Endangered Plant Species in the Context of the Convention on International Trade in Endangered Species of Wild Fauna and Flora and the Global Strategy for Plant Conservation1

“…The wild, native guanaco was replaced by exotic livestock (sheep), and fences and wires started dividing the landscape. Competition with sheep, hunting, and habitat degradation due to overgrazing resulted in reduced guanaco densities, local extinction, and restriction to marginal, low-quality habitats (Baldi et al 2004). …”