Granivory in the Monte desert, Argentina: is it less intense than in other arid zones of the world?

In 1978, Mares and Rosenzweig assessed seed removal rates by granivores at a site in the northern Monte desert of Argentina, and concluded that granivory in South America is 'much depressed'. In this study, spatial and temporal patterns of seed removal by small mammals, ants, and birds in the central Monte desert were analysed, and results compared with data available from other arid zones of the world. Ants were found to be the most important granivores in spring-summer, while birds were more important in autumn-winter. No differences were found in seed removal rates between microhabitats in winter, but in the summer both ants and birds removed more seeds from under the canopy of shrubs and trees than from exposed microhabitats. The impact of ants appeared to be lower in South America than in other continents, but removal by birds at the study site was only exceeded in North America, and removal by mammals only in North America and South Africa. Results indicate that granivory in South America is not abnormally depressed. Instead, current data suggest that seed removal in North America is exceptionally high, and that low levels are actually the norm for most arid zones.