Predatory interactions involving large carnivores and their ungulate prey are increasingly recognized as important in structuring terrestrial communities, but such interactions have seldom been studied in the temperate Neotropics. Here, the large carnivore guild is limited to a single species, the puma Puma concolor, native prey populations have been drastically reduced and lagomorphs and ungulates have been introduced. We examined puma dietary patterns under varying abundances of native camelid prey – guanacos and vicuñas – in protected areas of northwestern Argentina. We collected puma feces from seven protected areas, and sampled each area for the relative abundance of camelids using on-foot strip and vehicle transects. In one area, where longitudinal studies have been conducted, we examined the remains of vicuñas and guanacos for evidence of puma predation in 2004–2006. We compared our results with a study conducted in 1978–1983, and contrasted the frequency of carcasses showing signs of puma predation with estimates of camelid abundance. Across sites, we observed a positive and significant relationship between camelid consumption by pumas and camelid abundance, with pumas about nine times more likely to consume camelids where the latter were most abundant. The temporal variation in predation rates on camelids differed by species. Guanacos, which did not change in abundance between periods, showed a slight decrease (1.5 times) in the relative frequencies of individuals killed by pumas. Conversely, vicuñas increased in abundance by a factor of ∼7 between periods, coinciding with an c. 3.4 times increase in individuals showing evidence of puma predation. Some protected areas of northwestern Argentina are conserving the trophic interaction between pumas and native camelid prey. This interaction may be the basis of the far-reaching community effects described for analogous systems on other continents. It also has implications for the possible recovery of or reintroduction of camelids to areas with high puma densities, where predation losses can be expected to be high, and possibly prohibitive.