BALDI Ricardo
The distribution and feeding strategy of guanacos in the Argentine Patagonia. A sheep-dependent scenario.
Año: 2000 vol. 7 p. 60 - 60
In this thesis, I study the feeding ecology and distribution of the guanaco (Lama guanicoe) and the domesticated sheep in the arid-lands of the Argentine Patagonia. First, I review the animal and environmental factors influencing herbivore foraging behaviour. Second, I concentrate on the association between guanaco and sheep densities in relation to food availability. I conducted replicated ground surveys of guanaco and sheep numbers in nine different sites, during two austral summers and one spring. Also, I conducted vegetation surveys and collected faeces to assess diet composition. I found that guanacos are not “browsers” and sheep are not “grazers” but both are “intermediate” feeders in terms of their foraging strategy. Guanacos and sheep have similar diets and show similar patterns of plant species selection. Food niche overlap between guanacos and sheep increased from spring to summer, as forage plants became scarcer in the environment, suggesting a potential for interspecific competition. The distribution of guanacos across sites was inversely related to the availability of the most important plant species in the diet of both guanacos and sheep. In contrast, I found a positive association between sheep densities and the availability of key plant species in the diet. Sheep densities were up to an order of magnitude higher than guanaco densities in sites where both species live sympatrically. Sheep densities accounted for most of the spatial variation in guanaco densities. Furthermore, within-site variation between seasons in guanaco densities were negatively related to changes in sheep densities. Since both herbivores selected a similar diet, the negative correlation between guanacos and sheep cannot be the result of fundamental differences in preferred food resources. These results suggest that interspecific competition may be occurring, and may have played a role in the marked decline of guanaco population during the last 100 years since the introduction of domestic sheep.